How to Identify and Manage Perennial Weeds (Without the Viral Sprays) - Ep. 303

[00:00:00] Last week we talked about mulch, and one of the big reasons that you'd put mulch down is to prevent weeds. And if it's annual weeds we're talking about, the ones that sprout from seed every year, then mulch does a pretty decent job. A thick layer kept topped up can knock out a huge percentage of those seedlings before they ever see daylight. But then there's the other category, the ones that don't care about your mulch, the ones that come back

[00:00:25] every single spring from a root system that's been building underground for years. The ones where you pull the top of the plant and feel briefly victorious, and then two weeks later there are five more shoots exactly where that one was, maybe more. Perennial weeds are a different beast entirely, and today we're going to talk about the most aggressive ones, what they look like, where they live, how they spread, and just as importantly, how to manage them in a way that's grounded in science.

[00:00:54] Welcome back to Just Grow Something. I'm Karin Velez, a market farmer and horticulturist, and we are continuing a theme that we started last week with our mulch episode. Today we have a lot of ground to cover. Pun intended. We're going to start with a regional deep dive into the most aggressive perennial weeds across the U.S. I'm going to give you identification characteristics because the first step to managing any weed is actually knowing what you're dealing with. And then we're going to walk

[00:01:21] through a management strategy that is based on the same integrated pest management principles that professional growers and extension services use, and that we have talked about before in terms of insect pests. The same principles apply to our weeds. And then we'll close with something I know a lot of you are going to want to talk about, the viral homemade weed killer recipes and why some of them are a

[00:01:45] really bad idea in the garden. Let's dig in. So before we get into it, a little note about eradication. You're probably not ever going to fully eradicate an established perennial weed. And this is not a failure on your part as a gardener. That is just the biology of these plants. The goal is management, suppression,

[00:02:14] keeping them from winning. And that is absolutely achievable with the right approach. I also want to start by acknowledging something else. A lot of the worst perennial weeds do not respect regional lines. Okay. Field bind weed has been reported in just about every state in the U.S. Canada thistle has been declared a noxious weed in over 40 states. So there's a lot of overlap here. What I'm going

[00:02:40] to do is highlight the weeds that tend to be especially problematic in each region, either because of climate suitability or prevalence or how aggressively they behave in those conditions. But that doesn't mean it's limited to those areas. There's a lot of crossover here. I also want to say before we get into this, that identification matters a lot because your management strategy

[00:03:04] will vary based on the weeds life cycle, its root structure and how it spreads. Treating a rhizomatous grass the same way that you would treat a tap rooted broadleaf is not going to get you very far. I'm also going to give you the scientific name or the Latin name for each one of these because sometimes regionally names can get switched around and I want you to know exactly what you're dealing with. So we're

[00:03:33] going to start with the Midwest and the Great Plains. So if you're gardening in Missouri, Kansas, Nebraska, Iowa, Illinois, anywhere across the Great Plains, you probably know these weeds. Okay, these are the ones that we deal with here at the farm. And we're going to start with the one that I personally have the most complicated feelings about, and that is field bindweed. This is convolvulus arvensis. Field bindweed, it's also known as perennial morning glory, and it is in the morning glory

[00:04:03] family. If you've got it, you know it. It is a low growing twining vine that produces small funnel shaped flowers that are white to pale pink. They are very pretty. I mean, they are literally a morning glory flower. The problem is, is they are very destructive. The leaves are arrowhead shaped, they are dark green, they are hairless, and they are about two inches long. So the main problem with field bindweed is that

[00:04:31] it produces vertical tap roots that can extend 20 to 30 feet below ground in the right soil conditions. And then the lateral roots can spread outward as a very extensive underground network. Only about 70% of the root system on field bindweed is typically in the top two feet of the soil, which is why repeated

[00:04:56] shallow cultivation often just stimulates more growth from those lower roots. Field bindweed, unfortunately, spreads both by seed and by those root fragments. And seeds can remain viable in the soil for 20 years or more. So it was first documented in North America as early as 1739. It was likely introduced as a contaminant in crop seed.

[00:05:20] And it has since been reported in every state and placed on 22 state noxious weed lists. So if you're trying to ID this, just look for those arrowhead shaped leaves and the small little morning glory style flower. And then it's got that trailing vining stem. They can get to about four feet long and they climb up

[00:05:43] through other plants or they even just lie flat on the ground. If you see it twining up your tomato cage or squash vine or your plants, that's field bindweed. The next one is Canada thistle or Cirsium arvense, which for the record did not originate in Canada, just like any of the other things that we call Canadian here in the States. I'm very sorry to my neighbors from the North. This is an invasive perennial from

[00:06:11] Southeast Europe and Asia. And it was introduced to North America in the early 1600s. It is now widespread across the Northern and Western US. It is a significant pest in agricultural systems and in pastures and in our home gardens. It is a creeping perennial. It spreads aggressively from both the seeds and its horizontal root system, which are rhizomes. So the plant typically grows about two to five

[00:06:38] feet tall. The leaves are long, they're narrow, they're irregular. They've got sharp spines along the leaves. But the key identification clue to know whether it is a Canada thistle or something else like a bull thistle or musk thistle is that Canada thistle does not have spines on the stem. And that's just a helpful distinguishing feature. The flowers are small, they're pink to purple. They are born in clusters at the ends of

[00:07:06] the soil. And each plant can produce about a thousand to fifteen hundred seeds. And those seeds can remain viable in the soil for up to 20 years, which sounds like that would be the main problem. But it's actually the root system that makes it so hard to manage. The roots can go up to 36 inches deep, spreading both vertically and horizontally and horizontally. And root fragments as small as half an inch can produce new plants.

[00:07:35] Fun! One more thing to know about Canada thistle is that it is diocious, meaning individual plants are either male or female. So that seed production only happens when both are present, which, given how it spreads, it sounds like it's pretty often. So the fluffy white material attached to each seed that's called a pappus, and it helps carry it on the wind in a manner that is very similar to dandelions.

[00:08:05] And then the third one for our area would be Johnson grass, which is Sorghum halepense. This is this is the bane of my existence. It is a warm season perennial grass. It can reach about six to ten feet tall in a good season. It is hard to miss once it gets going. It is coarse. It's a very erect grass. It's got leaf blades that can be up to 24 inches long and about one to three inches wide. And they have

[00:08:32] a distinctive pale color midbane that runs right down the center of the leaf. The seed head on it is a large pyramid shaped open panicle. So again, it's in the sorghum family. So think a sorghum grain, right? And it starts out greenish yellow and then it matures to a dark red or a purple. Actually another one that's kind of pretty, but it is so aggressive. It was introduced to South Carolina

[00:09:00] from the Mediterranean region around 1830 as a forage crop. And it has since become one of the most problematic perennial grasses in the country, particularly in the South and the Midwest and into the mid-Atlantic. It spreads both from those seeds at the top and from thick, creeping underground rhizomes. And those rhizomes are what allow it to dominate an area. They spread

[00:09:27] laterally and then they produce new daughter plants, just creating these really dense stands that also prevent the things that we want to grow, the other desirable species from establishing. If you've ever pulled these rhizomes up, you know what they look like, like crab legs. That's the best way I can describe them. They have the red marking on them, etc. So they're very, very distinctive and you know exactly what you're looking at when you see it.

[00:10:02] So the next area we'll talk about is the Southeast. The Southeast has a climate that is uniquely welcoming to aggressive perennial weeds. You've got long growing seasons, high humidity, mild winters, which means that some species that just wouldn't do very well anywhere else absolutely thrive in the Gulf states, the Carolinas, Georgia, Florida, you know, that whole area. And so the first one that we

[00:10:26] have to talk about is kudzu. This is Pueraria montana var. lobata, and it is perhaps the most infamous plant in this region. The vine that ate the South is what they call it. It is a perennial. It is a high climbing vine that was native to Japan and China. It was introduced to the U.S. in 1876 at the Centennial Exposition in Philadelphia. It was brought in as an ornamental and it was later promoted

[00:10:56] as livestock forage and it was widely planted for soil stabilization throughout the South. By 1946, there was an estimated 300,000 acres that were planted and the rest, as they say, is history. Of course, it escaped cultivation. And what makes kudzu so difficult is the combination of its vine growth

[00:11:20] growth rate because it can grow up to a foot per day in ideal conditions. And its deep starchy root crown that stores enormous reserves of energy. Surface removal barely does anything to kudzu. So if you're, if you're trying to figure out if it's kudzu, look for the leaves. They are alternate and compound and they're made up of three oval leaflets that can be about two to eight inches long. And the vine does produce

[00:11:50] violet flowers that are very fragrant from August through September that looks somewhat like wisteria. And then the stems are hairy and these vines can reach lengths of over 60 feet in a single season. Okay. Which is what makes it so absolutely destructive. Next up is yellow and purple nutsedge. This is Cyprus

[00:12:13] esculentus and Cyprus rotundus. So nut grass or nutsedge is also called nut grass and it is consistently ranked among the worst weeds in agriculture globally. And gardeners across the Southeast know exactly what I'm talking about. Both yellow and purple nutsedge are perennial weeds in the sedge family and they superficially resemble grass. But the way that you can tell them apart

[00:12:38] from true grasses is that sedge stems are triangular. So there's a phrase that's helpful. Sedges have edges, rushes are round, grasses are hollow right up from the ground. Not that I think you're going to remember that, but it's just, you know, it's a fun little moniker for, for helping remember what it is that you're looking at or identify what you're looking at. So the yellow nutsedge, that's the Cyprus esculentus,

[00:13:02] it's more widespread. It appears across much of the U.S., including the Midwest, we have it here, and in the Northeast, although it's especially problematic in the Southeast and along the Gulf Coast. You can tell if you've got yellow nutsedge in your lawn because it grows faster than most turf grasses will. So after you mow, it's going to grow much more quickly and you just see it sticking out in the

[00:13:27] lawns. The leaves are light green, they're kind of glossy, and then the flower head usually shows up in the summertime and it's this yellowish brown color. For the purple nutsedge, it's a little bit less widespread, which is good because it's a bit more aggressive where it does show up. And it, it really likes the warm tropical climates. And so the flower head on that one is like a reddish brown

[00:13:50] to purple. What makes both species so difficult is their underground storage system. So nutsedges grow primarily from small underground tubers called nutlets, and they're formed on horizontal rhizomes, mostly in the upper foot of the soil. And those nutlets can persist for years and they produce new plants even after the top growth is completely removed. They also resist many standard herbicides.

[00:14:18] And then that glossy leaf surface makes it harder for like contact treatments to stick. And then the final one for this region is Torpedo grass or panicum repens. This one is especially relevant for gardeners in Florida and the Gulf states. Torpedo grass is a non-native perennial grass. It can grow up to three feet tall. It forms these dense stands that totally displace the native species.

[00:14:43] It occupies thousands of acres of marsh in Florida, and it occurs in 75% of the state. Torpedo grass spreads aggressively through rhizomes that produce new shoots and roots at every single node. It likes those open sunny areas, but it can also handle the part shade. It even outcompetes bermuda grass in lawns, which tells you something about how aggressive it is.

[00:15:13] The next area is the Northeast and the Mid-Atlantic. So Pennsylvania, New York, New England, New Jersey, Maryland. There are several perennial weeds that cause particular trouble for you guys, including some that we also see here in the Midwest and then also in the Southeast. Japanese knotweed. This is Fallopia japonica. It is an herbaceous perennial member of the buckwheat family. It was introduced from East Asia in the late 1800s as an ornamental,

[00:15:39] and for stream bank stabilization. So of course it escaped cultivation and is now a significant invasive species across most of the Eastern US and the Pacific Northwest. Identification is pretty distinctive once you know what you're looking at. In the spring, it produces these reddish to purple shoots. And then as it matures, it develops hollow bamboo-like stems. And that's the feature that most

[00:16:05] people remember. It's got heart-shaped leaves that have a flat or slightly indented base. These guys can get to be about 10 feet or more, and it produces clusters of like small creamy white flowers in the late summer. The underground rhizome system. Again, this can spread more than 65 feet from the parent plant.

[00:16:29] Yes, you heard me correctly. 65 feet. It's why knotweed is so devastating. It can completely displace native vegetation. The rhizomes are also incredibly persistent. Even small fragments left in the soil can produce new plants. And there are also related species. There's giant knotweed, which is Fallopia saliconensis, and then a bohemian knotweed that is a hybrid, and these all cause similar problems.

[00:16:55] Another one in your area is mugwort. This is Artemisia vulgaris. And mugwort was actually introduced to North America as a medicinal herb and a flavorant. It has a long history in traditional medicine. It was used to flavor ale before hops became the standard. And of course, it has since spread across much of the eastern U.S., and it's one of the more difficult perennial weeds to manage in

[00:17:20] a garden beds. It has a distinctive, strong, resinous, almost sage-like smell when you crush the leaves. And that's usually your first clue. That's what you're dealing with. The leaves are deeply lobed. They're dark green on the top, but they're silvery white and woolly underneath. And so this is a key identification characteristic. Plants can grow three to six feet tall, and they have these tiny

[00:17:45] little brownish flower heads in the late summer. They're very inconspicuous. So mugwort spreads by seed, but its primary means of invasion is through lateral underground rhizomes. Are we sensing a theme here with these perennials? It's especially problematic in disturbed areas. So think like road size or garden edges or any area with bare or disturbed soil. And once it's established in a

[00:18:12] perennial plant bed, it is extremely difficult to remove because the rhizomes weave through the root systems of the other plants. And the final one for this area is poison hemlock, conium maculatum. And I want to spend some time on this one because it's classified as a biennial, sometimes perennial. And while it doesn't spread vegetatively like the rhizomatous weeds that we've been discussing,

[00:18:41] it is dangerously toxic and increasingly common along roadsides, in waste areas, near waterways, and yes, in garden edges. We have tons and tons of poison hemlock here. And it's been showing up in regions where it wasn't previously common. So it is spreading and identification is genuinely important from a safety standpoint. Poison hemlock is a member of the parsley family. That's the APACA

[00:19:11] family, okay? Which also includes carrots and celery and parsnips, right? Think about what the tops look like on all of those plants. That family resemblance is what makes it dangerous. It can be mistaken for wild carrot, what we call queen Anne's lace, or parsley, or even young carrot tops. So there are identification features that are going to distinguish poison hemlock from its lookalikes. The first is

[00:19:40] the stems. Poison hemlock has smooth, hollow stems with distinctive purple or reddish purple splots or blotches, okay? That purple spotting is one of the most reliable identification markers. Queen Anne's lace and wild parsnip do not have this. And Queen Anne's lace has hairy stems. We say Queen Anne had hairy legs so that we can remember which one is which. The second is the smell. When the

[00:20:08] leaves or the stems of poison hemlock are crushed, it has a strong, unpleasant, kind of musty odor. And then the third thing is the leaves. They are highly dissected and very, very fern-like. So they are similar to a carrot top, but they are larger and they are much darker green. So in the first year,

[00:20:31] the plant grows as a basil rosette that can look a lot like a carrot or wild parsley, but it's very low to the ground and much wider than what you would see in terms of a carrot or a parsley. In year two, it bolts very quickly up to like eight feet tall. And it gets these broad, flat-topped clusters of small white flowers in that

[00:20:57] arrangement that we call an umbil. This is an umbilophore. So the stem, the stem can get like 10 feet tall if it's in a really happy place, which seems to be my farm because we have battled poison hemlock for years. Now the interesting thing about that point is that poison hemlock reproduces only by seed. It does not spread vegetatively, but it is a prolific seed producer and those seeds can

[00:21:24] remain viable in the soil for two to three years. All parts of the plant are toxic to human and animals. Historically, if we look back, kids have been poisoned from using the stems because they're hollow like flutes or as pea shooters. So do not handle this plant without gloves. Do not mow or weed eat it without protective equipment. The fragments can actually be inhaled and it is toxic.

[00:21:52] So if you're not sure of your identification, contact your local extension office before you do anything else. The next area would be the Pacific Northwest. So Oregon, Washington, Northern Idaho, you guys have your own cast of perennial weed villains. Some of these are shared with other regions and some of them are more specific to your more mild wet climate. The first one would be that Canada thistle. Okay. We we've it's worth noting. You know, this is actually one of the primary perennial weed concerns

[00:22:22] for field and vegetable crop producers in the PNW. And it's actually listed in King County, Washington as a noxious weed. And they have very specific management obligations if you see this thing pop up. So the cool, moist climate suits Canada thistle very well in your area. Quack grass is another one. This is a lemus repens. This is formerly known as agripyron repens.

[00:22:49] It is a creeping perennial grass. It causes problems across much of the U S but it's particularly notable in the PNW also here in the Midwest, also a little bit in the Northeast. My alma mater, Oregon State University describes it as an aggressive perennial that grows up to four feet tall from seeds. And yes, once again, those creeping rhizomes. So quack grass has a flat, somewhat rough

[00:23:16] leaf blades that are about a quarter to a half inch wide, and they are four to 12 inches long. The most reliable identification feature for quack grass is a pair of small claw like structures. We call them, they're called oracles and they wrap around the stem at the point where the leaf blade meets the leaf sheath. And these are pretty distinctive and they're not actually present on

[00:23:42] most other grass lookalikes. The seed head is a slender spike. It's very similar in appearance to an annual ryegrass or wheat, which can also cause confusion in identification. Quack grass spreads primarily through sharp tipped rhizomes. The tips are actually pointed and they're hard enough to pierce through other plant roots and bulbs. And then of course the rhizome fragments, you know, you can have,

[00:24:09] leave just an inch behind and it will generate new plants. This is why tilling a quack grass infestation without follow-up management can make things significantly worse. So you're effectively multiplying the number of fragments that are in the soil. And then there's Japanese knotweed. We covered that in the Northeast section. It is also a major concern in the PNW, particularly along riparian corridors

[00:24:34] in like Oregon and Washington. The Washington State Noxious Weed Control Board lists it as a Class B Noxious Weed. And given the extension river systems in that region and knotweed's affinity for stream banks, it spreads super aggressively throughout the waterways and it is extremely difficult to manage once it's established in those environments. And then finally, let's touch on the Southwest and the

[00:25:00] Intermountain West. So Arizona, New Mexico, Nevada, parts of Utah and Colorado. Water availability shapes which weeds dominate in this area because we're talking arid and semi-arid, right? But field bindweed, which we already covered, is extremely prevalent here. It thrives in disturbed soils of irrigated gardens

[00:25:25] and farms. And then yellow nutsedge also shows up in those irrigated areas. Johnson grass also extends into the Southwest. It's a significant problem in, again, irrigated areas and those disturbed roadsides in the warmer parts of the region. I also want to mention a weed that's more of a regional specific here. That's Dallas grass. It's paspalum dilatatum, dilatatum, I think, maybe. Anyway, it's a warm

[00:25:54] season perennial grass. It's found across the southern tier of the U.S., so from California to Florida. It is particularly problematic in the Southwest and in the South. It forms very dense coarse clumps that are very difficult to remove manually. And once again, it spreads by both seed and rhizomes. All right, that's our regional tour of the U.S. I know that was a lot of information, but I want you to be able to look out into your garden and actually know what you're dealing with

[00:26:23] before we talk about management because the management strategies are going to vary based on what you've identified. So we've talked before about integrated pest management or IPM. Okay, it's a framework that most extension services and professional growers use when approaching pest

[00:26:48] problems of any kind. We generally think of it in terms of insects and diseases, but the principles also apply to weeds. The core idea is that you start with the least invasive, lowest risk strategies, and then you move toward your more intensive interventions, but only when necessary. Okay, so you use a combination of methods rather than just relying on any single approach.

[00:27:18] So IPM is a system that regulates pests by using a variety of control measures, including mechanical, cultural, biological, and chemical. So for perennial weeds specifically, this framework is especially important because as we have established, no single method is going to eradicate a well-established

[00:27:41] perennial weed. The goal is to use the right combination of tools applied at the right times consistently enough to suppress the growth and prevent the spread. Okay, so let's walk through the steps. The first one is prevention and exclusion. And unfortunately, this is the step that gets skipped most often because by the time people are thinking about weed management, the weed is already there.

[00:28:07] But for anyone establishing a new garden bed, expanding an existing one, or bringing in new materials, prevention is absolutely the highest leverage thing that you can do. Weed management is much simpler if weeds do not become established in the first place. And exclusion is by far the best preventative measure we have available. So what does this look like in practice? Scrutinize what comes into your

[00:28:37] garden. Okay, perennial weeds can be introduced in purchased topsoil, which is one of the most common ways. If you're bringing in topsoil, compost, fill dirt, whatever, ask where it came from and be vigilant in keeping an eye out for any new growth in the weeks after that you add it. Okay, rhizome fragments can survive in compost that hasn't been properly heated. Plant material is another way. Okay,

[00:29:02] always inspect any divisions or transplants or bare root plants for any kind of hitchhiking weed roots or rhizomes. Machinery and equipment that's been used in infested areas can carry seed and root fragments. So if you have work being done, and they're bringing in machinery to do that, that can be something that transports it. Even clothing or pet fur or mowing equipment can transport weed seeds.

[00:29:28] And an often overlooked prevention step, but one that's becoming more and more important is don't plant ornamental species that are known to be invasive in your region. Japanese knotweed was a garden plant once. So was mugwort. So was kudzu. Okay, when you're choosing perennial plantings, check your local extension's invasive species list before you put something in the ground. You would assume

[00:29:55] that if something is considered aggressive, invasive or noxious that the garden centers wouldn't sell it. You would be assuming wrong. So we have to take responsibility for what comes into our garden. Okay. If you're establishing new beds in an area where perennial weeds are present, then consider a pre-establishment phase before you plant anything. That might mean a season of suppression treatments

[00:30:23] before putting in your desired plants. But this is far easier than trying to manage weeds after the fact. So step two in IPM would be cultural controls. And these are the practices that you build into how you garden that creates conditions that are less favorable for weeds and more favorable for the plants that you want. They are enormously effective as part of an overall system. So competition

[00:30:52] is a very powerful cultural tool. A bed that is densely planted with vigorous desired plants will have far less weed pressure than a bare or sparsely planted bed. Close spacing in both your flower beds and your vegetable gardens where plants are allowed to fill the entire space helps suppress weeds by shading the soil surface and out competing for resources. So block planting rather than row planting is especially

[00:31:22] effective for this reason. This is a part of the benefit of heavily interplanting your garden. Give the plants just enough space based on their mature size and adhere to that high, low, fast, slow mantra. And that will not only give you a higher production level, but fewer weeds. Mulch is a cultural tool and it's worth addressing its limitations with perennial weeds specifically.

[00:31:48] A good two to four inch layer of organic mulch is excellent at preventing annual weed seeds from germinating. For perennial weeds with established root systems, it is much less effective. We talked a lot about this in last week's episode. It will likely not effectively control established perennial weeds that are growing from the root. What mulch can do is make the emergence of those shoots easier to spot

[00:32:13] and easier to pull while they're still small. In fact, I had a listener comment on last week's episode in Spotify specifically about how much easier it is to pull perennial weeds that grow through wood mulch. And I just so happened to have been experiencing that exact thing that day in my own garden with field bindweed and Johnson grass. So keep your mulch maintained and topped up, but don't expect it

[00:32:39] to solve an established perennial weed problem on its own. You should also avoid creating disturbed soil without a plan. Perennial weeds absolutely love disturbed areas, roadsides, construction zones, bare ground after you've removed something. So when you expose bare soil, you're basically creating an opportunity for these perennials to move in. So have a plan for what goes in that space quickly,

[00:33:08] whether it's a mulch layer or a cover crop or your next round of plants. This is why I feel like it's important to maintain a calendar as part of your garden journal or your garden plan. And maintaining your soil health also counts as cultural control. So a healthy, well-structured soil with good fertility supports vigorous crop growth that can better compete with the weeds. And it doesn't mean over fertilizing. It means building soil organic matter over time so that your

[00:33:38] desired plants have the advantage over the ones that you don't want. Step three is mechanical controls. Mechanical control means physically removing or disrupting the weed. So for perennial weeds, this requires a little bit more thought than just pulling them out because of those root systems that we've been talking about. So your first step would be hand removal. Okay. And for any perennial weed,

[00:34:06] hand removal needs to focus on getting as much of the root as possible, not just the top growth. Now, repeated removal of top growth does eventually deplete the root carbohydrate reserves, but this takes significant time and multiple growing seasons of consistent follow through. And watch out if you miss the window to cut back by even a little bit, because it doesn't take much for that photosynthesis to build those energy stores right back up again in the root system. And then you're

[00:34:35] practically starting over. So use a soil knife, a fork, a digging tool of some sort to get underneath the root system and work in moist soil when you can, because it helps you get more of the root out intact. Remove all fragments from the garden. Do not compost perennial weed roots unless you have a hot compost system that reliably reaches temperatures above 130 degrees Fahrenheit. What I do is I lay

[00:35:02] the shoots and the roots out flat in a very sunny area for like a week to 10 days to just cook them down to a shriveled crisp. And then I toss them in the compost. Your next version of mechanical control would be repeated cultivation. Now, this is important for perennial weed control because it encourages that repeated growth, which can reduce the carbohydrates in the weed storage structure over

[00:35:28] time. But the critical caveat to this is that you need to be careful about which weeds you're cultivating around. So for the rhizomatous weeds, bindweed, quackgrass, Canada thistle, nutsage, not nutsedge, nutsedge, and not weed. Deep or aggressive tilling is actually going to fragment the root system more and it's going to spread it further throughout your bed. This is counterproductive.

[00:35:55] So for these species, the shallow cultivation to remove the top growth is appropriate, but avoid the kind of deep disturbance that would break up and redistribute those root fragments. This is how we managed to rid an entire field of field bindweed, but it took us three years of mowing flat, tilling shallow, mowing flat, tilling shallow. And then we finally got rid of it. Some extension guides recommend

[00:36:22] tilling as part of an integrated strategy specifically because the flush of new growth can then be targeted with follow-up treatments, but this requires careful timing and follow through. So if you cannot stay on top of it, this may not be a technique for you. So a mechanical control that I highly recommend is soil solarization. So this is a non-chemical technique that uses the sun's heat to kill weeds, weed seeds,

[00:36:50] and even soil pathogens. And it is extraordinarily effective. And I am set to do this in July in a particularly weedy section of one of our fields. What you do is you moisten the soil and you till it lightly to about six inches and then you cover the entire area with clear plastic. And it has to be clear, not black. You seal the edges and then you leave it in place during the hottest weeks of summer for like

[00:37:16] four to six weeks. The goal is to raise the soil temperature so high that it's lethal for the weed seeds and the root fragments. Now I have to emphasize here clear plastic solarizes, okay, using solar radiation to heat the soil. Black plastic occludes, so it's blocking the light, but it's not achieving the same temperatures. Black plastic tarping works really well for annual weeds, but it is much less

[00:37:44] effective for perennial weeds than the ones that have the persistent root systems. You need the solarization, okay? Now a key point to this is that after solarization you should avoid deep cultivation that would bring the viable weed seeds back up to the surface or the root fragments back up from below the treated zone. This is important. The solarization only works in the zone that it heated. So have a plan

[00:38:09] to layer on some thick compost on the top of the bed and keep the cultivation to a minimum from then on out. Solarization is most effective in climates that have long, hot summers. It is a great tool in the south, the southwest, and into the midwest. It's a little bit less effective in your cooler, cloudier climates, and it has limited effectiveness on the really, really deep-rooted perennials like field bindweed. For that you've got to use the mow

[00:38:36] and till method that we used. And then your final mechanical control, which is also a really good one, is smothering and sheet mulch. So heavy smothering, which is like using layers of cardboard top with a deep organic mulch, we're using wood chips, can suppress some perennial weeds by eliminating the light and making it physically difficult for those sheets to emerge. And this is working really

[00:39:00] well for our Johnson grass problem, but it does work better on some species than others. Okay, kudzu, knotweed, and bindweed are persistent enough to push through or just grow around the standard sheet mulch layers if you give them enough time. It's definitely easier to manage them at that point, but for those weeds smothering needs to be a part of a longer-term strategy and it may have to be

[00:39:26] combined with other methods. So step four to IPM is biological controls. And again, we normally are talking about this in terms of like insect and disease management. Biological control just uses living organisms, so insects or pathogens or other plants to suppress weed populations. And this is primarily a tool used at like a landscape or agricultural scale. It's generally not something that home

[00:39:56] gardeners typically implement directly. And a lot of this is still being experimented with, but it's worth understanding how this is being attempted on a larger commercial scale. Biological control methods with insects are super complex and they have to be used with caution. The insects that are introduced have to be able to establish themselves. They have to be able to reduce the weed population without eliminating their food

[00:40:22] source. And they also must not attack beneficial plants or become pests themselves. So there are USDA approved biological control agents for some of the species that we've talked about. There are two biological controls that have been released for field bindweed, a gall mite and an owlet moth, but establishment has

[00:40:48] been poor. The results have been fairly limited. Canada thistle is another one. It has several insect and pathogen biocontrol agents that are under study, but none of them are reliably effective yet. So at the home garden level, what biological control really means is using competition from cover crops, dense plantings, or encouraging beneficial insects that may affect pest populations sort of indirectly.

[00:41:18] Growing dense competitive cover crops and off-season beds can absolutely help suppress some perennial weeds because you're shading and you're also competing for resources. That's about the best that we can do at the home garden scale. And then the final step, remember we work from least offensive to most offensive or least aggressive to most aggressive depending on how you look at it. So step five in IPM would be chemical controls. And I want to

[00:41:46] address chemical control directly because it is often necessary for established perennial weeds and pretending otherwise it doesn't serve anybody. The key principle for perennial weed chemical control is this. Systemic herbicides that move through the plant into the root system are what you need. Not contact herbicides that only affect the tissue that they touch. Okay, this is why the

[00:42:14] vinegar sprays don't work on perennial weeds, but we'll talk about that in the next section. The best timing for systemic herbicide application on perennial weeds is in the fall as the plants begin to move the carbohydrates down into their root systems in preparation for winter dormancy. A systemic herbicide applied at that time will be translocated to the roots along with those carbohydrates, which is

[00:42:42] exactly what you want. Treating in the fall is more effective than treating in the heat of the summer when the plants may be stressed out and not actively translocating. Now I'm not going to make specific product recommendations here. Herbicide registrations change, label requirements vary by state, and what's appropriate depends on what you're treating, where you're treating it, what's growing nearby, and your personal gardening philosophy. What I am going to strongly encourage you to

[00:43:12] do is read the label completely before using any herbicide product, contact your local extension office for region specific recommendations, and never apply herbicides near water without understanding the specific label requirements for that situation. Remember, I've said it before, the label is the law. And understand that multiple

[00:43:39] applications are almost always necessary. No single chemical application will eradicate a well-established perennial weed. So expect to commit to a multi-season management plan. Now we have never used any type of herbicide anywhere on any of our properties. I use all of the other methods that we talked about today to

[00:44:02] manage the issues, but your garden, your choice, just be sure to choose wisely. All right, let's talk about the stuff that's all over social media. I get it. There is a very appealing idea in the notion of mixing up the spray from things in your kitchen cabinet and eliminating the weeds in your garden without any chemicals.

[00:44:32] It feels natural. It feels natural. It feels safe. It feels like you're beating the system. And there are websites and Pinterest boards and Facebook groups that will enthusiastically tell you that the secret combination of vinegar, salt, and dish soap is all you need. How about we look at what the science actually says? So there was actually, I think it was the University of Connecticut extension that published a detailed

[00:45:00] research review on homemade pesticide issues. And it addressed exactly this recipe that we're talking about, the vinegar and dish soap and salt combination. Okay. The key point that they started with in that research review was that these mixtures are pesticides. Okay. They are intended to kill a pest, that pest being

[00:45:29] a weed. The ingredients being familiar household items does not make them non-toxic or risk-free. And being willing to admit that changes how you think about using them. So let's talk about what each of the components actually does. Vinegar is acetic acid and at high concentrations, 20% acidity, which is

[00:45:55] agricultural strength vinegar that is much higher than the 5% table vinegar in your pantry. It will burn and desiccate plant tissue on contact. It is a contact herbicide all by itself. It kills what it touches. The critical limitation is it does not move into the root system. So for annual weed seedlings, it can be somewhat effective. For established perennial weeds with extensive root systems, burning the top growth

[00:46:25] is essentially meaningless. The root will just regenerate new shoots within days. So for young weeds with only one or two leaves in a walkway or in a driveway, sure, vinegar can absolutely be useful. For established perennials, it is not. The second component is dish soap. Dish soap acts as a surfactant. It helps the

[00:46:49] solution spread across waxy leaf surfaces rather than beading off. It has no weed killing properties of its own. It does make the vinegar somewhat more effective as a contact treatment. This is why when you make a homemade insecticidal soap, you should not use dish soap because you're breaking down the waxy surface of the leaf cuticle on the plant that you're trying to save, which opens it up to pathogens.

[00:47:16] So for insecticidal soap, you should use Castile soap, which doesn't have any surfactants, but that is what is basically helping it stick to the plants when you use it. Okay. So the dish soap in this concoction is just acting as a surfactant. Salt is where the real problem lies. Table salt, sodium chloride, can kill plants. But to use enough of it to kill weeds effectively,

[00:47:42] it causes more harm to the soil than it does to the weeds. Salt builds up in the soil. Unlike vinegar, which dissipates relatively quickly, salt is persistent. It degrades soil structure. It harms earthworms and the beneficial soil microbes. And it can leach laterally into areas where you do want plants to grow. So repeated applications of a salt containing spray in a garden bed can render the soil

[00:48:11] inhospitable to any plants, not just weeds for a significant period of time. So if you want to use this type of mixture at all, use it on hard surfaces like driveways and patios where you don't want any plant growth and skip the salt even then, if you're anywhere near lawn or garden areas and do not use

[00:48:34] it, you know, in or near your garden beds. Now, beyond the vinegar spray problem, there are a few other commonly recommended approaches that are worth thinking critically about. Boiling water is sometimes promoted as a natural weed killer. It will kill anything it contacts, including soil microbes and earthworms and beneficial organisms in the soil. So for a crack in the driveway or a patio, fine. In the

[00:49:02] garden, you're damaging the soil biology that you've been working really hard to build. And then landscape fabric is promoted as a long-term weed solution. We talked about this last week. Colorado State University Extension actually addressed this directly and offers a perspective that you might not have thought about. They describe landscape fabric as more of a deferred maintenance technique than a low

[00:49:30] maintenance technique. And we talked about why, right? Weed seeds that blow in and germinate on top of the fabric are harder to pull because their roots go through the fabric. So over time, that fabric prevents organic matter from incorporating into the soil, which is reducing the soil life and the structure. So for established perennial weeds with deep root systems, remember that landscape fabric was not an effective

[00:49:56] control. The roots can just, you know, grow right through it or grow around it. So if you're going to use landscape fabric, keep it in mind that is a short-term solution and it needs to be pulled up at the end of the season. Otherwise it needs to be left in areas that are specifically for like landscape purposes. Aggressive tilling as a weed solution. You know, as we talked about earlier, this is actually a

[00:50:21] significant problem for the rhizomatis weeds specifically. Tilling a quack grass patch, a nutsedge infestation, or a bind weed stand without a follow-up management plan just distributes the root and the rhizome fragments throughout your bed. And it makes the problem actually substantially worse the following season. So if telling is part of your management approach, it needs to be combined with other methods and

[00:50:49] followed up consistently. And then pulling as a one and done solution. I think we've established throughout this episode that perennial weeds, you know, one round of hand pulling is the beginning of a management relationship, not the end of one. Mechanical disruption, which is what hand pulling is, needs to happen repeatedly across multiple seasons to exhaust the root system. One pull doesn't do it.

[00:51:18] Consistent, well-timed, repeated intervention does. Okay, that was an absolute mouthful and that is enough for today. I want to close with something that I said at the top though. You are probably not going to fully eradicate an established perennial weed and that's okay. Okay, the goal is management, suppression, keeping them from expanding their

[00:51:45] territory, preventing them from setting seed, wearing down those root reserves over time with consistent strategic intervention. The gardeners who win the long game with perennial weeds are the ones who understand the biology of what they're dealing with, make a plan and execute it with consistency. They learn what they're growing against and they respond with the right tools at the right

[00:52:10] time. And now you have all the tools. There are 29 references in the show notes today. I'm linking to all the extension publications and the peer reviewed sources that I used for this episode. Hopefully a little weed identification and proper IPM plan will have you on the way to better managing the perennial weeds in your area. Until next time, my gardening friends, keep on cultivating that dream garden and we'll talk again soon. Keep on Thank you.