Mulch is one of the gardeners’ best friends and the best types of mulch help retain water in addition to keeping out unwanted weeds. Let’s cover a few different options for mulch that serves as weed prevention in your garden.
Straw. Straw is a fantastic, natural mulch for your garden. Using straw mulch around the plants and in your pathways serves multiple purposes. First, if you lay it down thick enough, it will choke out most annual weeds. What few do poke through are easy to spot and easier to pull before they get out of hand. This also applies to those pesky perennial weeds – they’re easier to see as they pop up through the straw and you can yank them while they’re still tender and haven’t had a chance to set any seeds to spread. Second, straw will retain the moisture around your plants. It prevents soil moisture from wicking to the surface and evaporating away. Third, straw will decompose slowly over time. This is great for your soil as it adds needed nutrients and biological material necessary for plant growth, but it generally does not decompose during the same season you are growing. Once the garden is done for the season, leave the straw on the ground. You’ll come back in the spring to find the soil easier to work with and even richer than before – you probably won’t even have to till the soil, which is even better for long-term soil health and for weed prevention.
Just try to keep the straw from touching the base of your plants. If they’re too close, it can encourage slugs or rot at the base of the plant from excessive moisture and can provide a haven for certain garden pests that like to invade the base of plants.
Keep in mind that straw will have a cooling effect on your soil. For cool-season crops that like the reduced soil temperature, like broccoli and cabbage, this is great. Plants that tend to bolt, or go to seed, before generating a useable crop because they got too hot too early will definitely benefit from the cooling effects of the hay or straw. But, for heat-loving plants like tomatoes and peppers, this may reduce your yield. Be sure to pull straw mulch back prior to planting warm-season crops to allow the soil to warm up faster.
Other Organic Materials. You can use grass clippings, dried leaves, pine needles and even sawdust as mulch for your plants. These will all break down slowly and work their way into the garden soil as a boost to the soil composition. Glass clippings are especially good sources of nitrogen, so plants that need that boost will enjoy grass clippings. Just make sure you research the nutrient needs of your plants before using grass as a mulch. Some plants, like tomatoes, like early availability of nitrogen but need more phosphorous later on to develop their fruit. Too much nitrogen will discourage flowering and reduce your yield, so use grass clippings wisely. Leafy greens will always benefit from a boost of nitrogen.
Additionally, grass clippings should be sun-dried for a day or so before adding to the garden. And avoid using clippings if the lawn has been treated with herbicides or pest-control sprays. These could be detrimental to your garden plants.
Be aware these types of mulches are also prone to cooling the soil, much like straw.
Paper. Using thick layers of newspaper or other discarded paper, or paper products like cardboard, in your walkways, in the bottom of your raised beds and in between your plants is also very effective at keeping weeds at bay. The paper will also break down and work into the soil like a form of compost and is really effective at helping retain moisture, just keep in mind you’ll need thick layers so they don’t decompose too quickly. Don’t use slick, shiny papers, like the ones you get in some mailed advertisements, as the inks in them can harm the soil in your garden and they may not break down as effectively. If you’ve got access to a lot of paper or carboard, this is a good way to go. If you’ve only got a few, use them strategically along with other mulches in the most weed-prone areas.
There are also commercial weed barriers made from biodegradable paper products that you can buy online and in garden centers. They come on a roll, often with planting holes already spaced for you. These can remain in place at the end of the season, to biodegrade into the soil for the next season. They are effective unless you get a really good amount of rain during your season, which may cause them to break down prematurely and allow weeds to push through. We’ve used them with our onion plant with some success in the past.
Landscape Fabric. This weed barrier is sold in rolls and is placed beneath mulch in landscape beds to prevent weed emergence. You can use landscape cloths in the bottom of raised beds to achieve the same effect, but you can also use them as an effective mulch around your plants. Roll out the landscape fabric and then cut holes where your plant will go, leaving the remaining area to be covered by the cloth to block weeds and trap in moisture. There are several different types of these cloths. Some are very thin material that does break down quickly over the season, but they don’t really help with the nutrients in the garden soil. I suggest avoiding those and using a thick layer of newspapers instead, which is just as effective and more beneficial to the soil. There are much thicker landscape fabrics that don’t break down and this is what we use in our fields for weed-prone crops like tomatoes and peppers. It’s a thick, woven product, it’s heavy, and very effective at keeping the weeds out, but must be pulled up and put away at the end of the season. If you don’t, you’re doing your soil and soil microbes a disservice by not allowing air and moisture to move in during the off-season and leaving the fabric to weather in the winter. So, use it responsibly.
This is a type of mulch that retains heat, especially the heavier fabric types. Great for tomatoes and peppers, not so much for plants like greens or broccoli. So, plan accordingly.
Black Plastic. Black plastic mulch can be used as a very effective barrier against weeds and a way to retain moisture. It’s almost the same texture and consistency as a black plastic bag. The problem with it is that it needs to be removed at the end of the season and it cannot be reused. This makes it a single-use plastic that is impossible to recycle, which is not something we are fond of. Also, some plants don’t like to be in contact with black plastic, like cabbages, and can rot where they touch it. It’s also more difficult to get water to the root systems of plants, usually requiring a drip line to be run beneath the plastic. There are biodegradable versions of this that break down at the end of the season, so there is no requirement to remove it. We’ve seen this sort of shredding in fields and not really decomposing completely and it’s just not one of our favorites for home gardeners.
Same thing here as for landscape fabrics. Black plastic will heat up the soil, so if you’re trying to warm the soil and transplant earlier or use in an area designed for heat loving plants, great. If not, you may want to opt for something different.
Wood Chips or wood mulch. These are the types of mulch you see used in flower beds. You can make your own by simply chipping up trimmings from the trees in your yard. Or you can buy it in bags at your local garden center. Just know that these chips can sometimes contain pesticide residue and will not provide much in the way of nutrients for your soil, since they break down more slowly. Also, they may get in the way when you try to work the beds the following year. This is our least favorite choice for the garden and don’t really recommend it, except in perennial areas. They do work well for areas where oregano, sage and other plants return year after year. I will say, though, if you keep permanent beds in your garden and use wood chips in the walkways to mark the paths, they work great for keeping the weeds out of those areas. This is actually our favorite choice for our pathways, but we don’t ever use them as a mulch in annual garden beds. It is good for perennial areas, though.
Stones and other inorganic materials. Decorative stone is generally good for areas where perennial plants, like herbs or perennial flowers, will stay put for years. They are good to keep an area looking nice, combat weeds and retain moisture. In the annual vegetable garden, though, it’s not recommended. Like wood chips, they will be in the way for working the garden the next season.
Ground cover/companion plants. The final option is to use a living ground cover or low-growing cover crop, like a companion plant that acts as a living mulch. You need to be selective in this instance, because you want a plant that will complement the one you are mulching. For example, we’re using a trailing nasturtium as a living much in our tomato plants this year. Not only will the trailing habit of the nasturtium fill in the spaces around the base of the tomato plants to choke out weeds and retain moisture, but the blooms of the nasturtium attract beneficial insects that prey on insects that attack the tomatoes. And, as an added bonus, the blooms of the nasturtium are edible, and make a great addition to our salad mixes we sell at our farm stands.
Another example is using winter squashes planted between sweet corn. The squashes sprawl, acting as a ground cover for weed prevention and moisture retention, and use nutrients at a different time than the sweet corn does. Any ground cover that doesn’t compete for nutrients with the crop you’re growing makes a suitable living mulch and will shade the ground to help retain moisture.
Compost. Not only is compost a good way to add biota, microbes, and soil texture to your garden, a thick layer of compost can also act as an effective weed barrier and will help retain moisture. A thick layer, from two to three inches or more, should be enough to prevent most weed from coming through. At the end of the season, just leave it in place to work itself into the rest of your garden soil as a great amendment. Like the other organic mulches, check your soil nutrients and the nutrient level of your compost if possible, to be sure you’re not throwing things out of whack.
No matter which mulch you choose, try to match the mulch with the crop and the soil conditions. Experience will help with this a little bit once you’ve got a season or two under your belt, but know that university field tests have shown using a mulch can increase your yield by 30 percent or more (or, you can look at it as NOT using mulch can reduce your yield by 30 percent or more). Not to mention the time saved from less weed pressure and less watering and the benefits to your soil structure and top soil.
And even if you do lay mulch down, you could still have some weeds pop up. If you attack those weeds as soon as they rear they’re little heads, you’ll increase your chances of eradicating them. Young weeds have small roots, making them easier to pull and destroy.
Your Friend in the Garden,
Resources:
Ep. 10 - Garden Talk Tuesday: Weed Prevention