Identifying and Controlling Persistent Weeds in the Garden

Weeds in the garden can be frustrating to any gardener and many of us don't want to resort to chemical means to control them. In this article, we’ll talk about the difference between annual weeds and perennial ones, the different ways they spread, and some strategies on how to prevent and control them. In most cases, you are not going to eradicate them completely, so managing them is the name of the game here. In some cases, this could take years and the frustration level may make you want to give up. But even the heaviest weed infestation can be controlled with a plan. 

Annual weeds are plants that complete their life cycle in one year or less. They usually produce a large number of seeds that can germinate quickly and spread widely. Examples of annual weeds are crabgrass, chickweed, lamb's quarters, and purslane. Perennial weeds are plants that live for more than two years. They have deep roots or underground stems that can store food and water, allowing them to survive harsh conditions and regrow after being cut or pulled. Examples of perennial weeds are dandelion, bindweed, nutsedge, thistle and Johnsongrass. There are biennial weeds as well, like mullein, but I classify biennials in the perennial category because methods of removal are the same.

It is helpful to know what the weed is you're dealing with in the case that these things are dangerous to handle, like giant hogweed or poison hemlock, but just knowing the signs of it being perennial or an annual is more likely to be helpful in the eradication. If you want to know what exactly you’re dealing with, there are often lists of your local common weeds on your department of conservation website, local university extension websites, weed identification links on university websites by region, and you can use Google Lens to take a picture of the weed and do a search that way. Another way to identify them is to find something in your garden that you’re growing intentionally that looks similar to the unwanted plant and you’ll get an idea of the plant family it belongs to and its growth habit. For example, field bindweed is in the morning glory family and the flowers look almost identical. Johnsongrass is a sorghum, and the seed heads look very similar to the cultivated types. Purslane is in the portulaca family, just like the decorative ones we plant in hanging baskets and flower beds.

It bears noting that some of these “weeds” often are a foragers dream. Lamb's quarters and purslane are prized edibles, cleavers are used for cleansing the lymphatic system, dandelion has tons of good properties to it, mullein is medicinal, etc. So, do with that information what you will.

So, whether they are an annual or a perennial, both types of weeds can be persistent in the garden, and they sometimes require different strategies to control them. Here are four steps that you can follow to control persistent weeds in the garden:

Mulch over them. Mulch is a layer of organic or inorganic material that covers the soil around your plants. It helps to retain moisture, prevent erosion, improve soil quality, and suppress weed growth. You can use shredded leaves, cardboard, straw, wood chips, even commercial compost as mulch. Apply a thick layer of mulch (at least 2 inches) around your plants and between rows. This will prevent most annual weeds from germinating and makes it easy to see new weed seeds that have blown in if they do manage to sprout on top of the mulch, and they are very easy to pull at that point.

For perennials, mulch can help choke out the species that are the least aggressive in their initial growth, but you’ll need a very thick layer, closer to four inches. And most perennials have extensive root systems which means they have lots of energy stored up to help them push through many layers of dirt and mulch. But the mulch will make it much easier to spot these weeds as they push through and easier to pull them as they do. After doing this over and over again, you will have exhausted the energy reserves of the root system and the weed will eventually die off. Persistence is key here. If you let them go too long after sprouting, they will put more energy into those storage organs and the cycle will continue indefinitely.

Exclude the light. For persistent weeds or a high volume of weeds you need to deprive them of light completely. This will weaken their root systems and prevent them from resprouting. You can use dampened newspaper or brown cardboard to cover the soil around your plants. Then cover that with a thick layer of mulch to hold it in place. Another way to do this is to cover the entire bed with heavy-duty black landscape fabric to both exclude the light and give a physical barrier. This works fantastically well for an area that has a ton of annual weeds that were maybe brought to the surface by tilling. Unfortunately, some of the toughest perennial weeds like nutsedge and Johnsongrass will perforate the black landscape fabric, so mulching over top of the fabric with straw or something else may also be necessary if you’ve got a bad infestation. With perennials weeds, it may take a few years to choke them out completely and we have to be vigilant in pulling them when they appear.

Pull them out or dig them up. Sometimes, the best way to deal with weeds is to remove them by hand or by using any myriad of tools available for this purpose. This is especially effective for young annual weeds or isolated weeds that have not yet established a strong root system. Just make sure you remove all parts of the weed, including the roots, rhizomes, tubers, bulbs, or runners. Even a one-inch fragment can allow them to regrow. Which is why it’s so hard to eradicate perennial weeds by just pulling them. But continuous pulling up of aggressive perennial weeds will eventually exhaust the root system and finally get you some relief. In my experience you are not going to completely eradicate them. But, once you get them under control you will have much less weeding to do. I can attest to this with the years we spent dealing with the field bindweed. I now only have the occasional specimen popping up and when they do they’re easy to spot and I can take care of the problem right away.

Mow them down. Another way to control annual weeds is to cut off their tops before they flower and produce seeds. Mow them down, or use a hoe or other garden tool that takes the tops off them. This will reduce their ability to photosynthesize and store energy in their roots. You can also use a stirrup weeder or hula hoe to just slice through the soil surface and sever the stems without disturbing the soil too much, so we don’t expose dormant weed seeds to sunlight and prevent them from germinating. With perennial weeds, this is another way to help exhaust their energy stores.

Keeping on top of weeds is an important garden task, but not the most enjoyable. Prevention, light exclusion, and manually removing them takes work but if we're persistent we can often get them under control without the use of herbicides.

Your Friend in the Garden,