(News article for August 12, 2023)
The last couple of articles (part 1 and part 2) have addressed vegetable planting decisions and ways to prepare the site to reduce weed problems. Even if you start with a weed-free area and have killed the roots of perennial weeds, some will still be able to return from seeds in the soil.
This article will address things you can do during the growing season to prevent problems due to weeds returning from seed. The next and final article in this series will address herbicides that can be used immediately before and while vegetables are in the garden.
After planting, the first several weeks (typically between two and six, depending on the crop) are the most important for weed control.
A practice that’s beneficial for both weed and disease management, as well as water conservation, is use of drip irrigation or a soaker hose that runs down the rows where vegetables are planted. This is helpful for weed management because it delivers water to roots of the crop but not to the row middles.
When you have a choice between seeding and transplanting – not all vegetables transplant well – the latter can help plants get ahead of weeds.
Mulching is a well-known weed management practice. Many types of materials can be used. Natural materials like leaves or straw help conserve soil moisture and add organic matter to the soil if they’re incorporated at the end of the season.
Mulch needs to be thick enough to block light from reaching the soil surface. When using natural materials like leaves or straw, a depth of 4 to 6 inches is suggested. If the material is dense, it’s probably best not to let it rest directly against the bases of the vegetable plants.
If you plan to use hay, find out if any herbicides with the potential to be problematic have been used on it. Most herbicides are not so persistent, but a handful of products – including ones that contain picloram, aminopyralid, or clopyralid – that are used to manage broadleaf weeds in pastures and hay fields are highly persistent and can damage many broadleaf plants.
Hay can also be a source of weed seeds if it comes from a weedy field. The same is true for grass clippings from weedy lawns.
Cardboard or several layers of newspaper can be used, along with something to hold them down.
A lot of commercial vegetable growers use plastic mulch, typically on top of raised rows, with drip irrigation tape below it. Black plastic mulch can be used in late winter or spring when warming the soil is beneficial to plant growth, and white plastic mulch can be used in the summer when excessive heat is a concern.
When managing weeds between rows using a hoe, tiller, or cultivator, only disturb the soil deeply enough to sever or uproot weeds just below the surface of the soil. Do it often enough that weeds do not get more than 2 to 3 inches tall. Working the soil too deeply may injure vegetable roots. Also, as mentioned in the previous article, tilling too deeply risks bringing more seeds close enough to the surface to germinate.
Keep hoes sharp so that they cut efficiently. If you plan to use a tiller between rows, be sure to space rows wide enough so that you can till without injuring vegetables.
Keep in mind that anytime weeds are allowed to grow long enough to go to seed – or to form underground nutlets, in the case of nutsedge – this is creating weed challenges for the future. Weed management is a long-term endeavor.
Let me know if you have questions.
Contact Mary Helen Ferguson.
A natural mulch and drip irrigation help manage weeds. (Photo by M.H. Ferguson)