Summer garden weed control considerations

Published 4:53 pm Wednesday, March 27, 2024

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As the weather turns warmer and signs of spring are all around us, it is time to begin thinking about the summer garden. I have done classes in Beaufort and Martin Counties recently with another coming in Washington County April 10 about spring/summer gardening. The classes cover multiple gardening topics and we cover a lot of ground in a short time about gardening. Objectives include Site Selection, Plant Selection, Propagating, Soils, Fertilizer, Amendments, Watering, Weeding, and Pest and Disease. Covering so much in a two-hour class is tough so I wanted to come back and talk about a few things in articles. The first article in the series is going to be about Summer Garden Weed control.

I like to consider weeds as plants that haven’t found a place yet. Many weeds provide beneficial support to invertebrates such as butterflies or even bees. For example, have you driven by a field lately? You will see that many of the fallow fields this time of year tend to have a purple hue from annual flowers called Henbit (Lamium amplexicaule) or a closely related cousin called Purple Dead Nettle (L. purpureum). These are both in the mint family and can be identified by their square stems when the purple flowers aren’t present. These are one of the earliest flowers to provide nectar for hummingbirds in addition to pollen for native bees and honeybees.

In the garden, however, they are often seen as competition for our vegetable plants. Weeds are such because they are opportunistic. They can establish/germinate, grow and reproduce quicker than our garden plants. This causes competition for limited resources such as nutrients, water, and often sunlight. When we look at weeds in the garden, we need to look at the critical weed-free period. This is the time frame for a crop when it is best for our desirable plants not to be in competition with weeds. Often this occurs when the plant is becoming established. Once plants begin to mature, we will have canopy closure. Canopy closure is the period after which our desirable plants shade out and out-compete the weeds beneath them. Annual weeds must have sunshine to germinate and flourish. Once we have canopy closure, the sunlight no longer reaches the soil to trigger the germination of new weed plants.

In the home garden we often do not achieve canopy closure, so what then? Most of us really do not like to use pesticides in the garden if possible, so we need to look at strategies to prevent weeds from germinating. One strategy is to shade the soil by using mulch in the garden. Using untreated grass clippings, wheat straw, or last year’s autumn leaves will work great. We need a good two to three-inch layer of an organic (in this case, organic means it was once alive) mulch to successfully stop the germination of most annual weeds. At the end of the season, the organic mulch can be turned into feed and encourage microbial activity within the soil profile. This is a huge contributor to building and perpetuating healthy soils in the garden.

If the weeds do germinate, use a stirrup type hoe to uproot the newly germinated seedlings. These are sold in different sizes and cost depends on where you purchase them. Using the stirrup hoe, simply walk the beds dragging the hoe across the soil to uproot weeds. If this is done once or twice a week weeds will have a hard time getting established. A bedded garden of about 1,000 square feet can be done in roughly 30 minutes. However, using organic mulch in the garden is a better strategy and is more sustainable on your back.

Lastly, we have chemical control of weeds. This can be difficult in vegetables because the list of selective chemistries is quite small. Using pre-emergent (PRE) applications will work well on some broadleaf annuals and most annual grasses but, this will only work well for vegetables that are transplanted into the garden.
Two of the main PREs have the active ingredients trifluralin or pendimethalin. These are marketed under different tradenames so make sure you read the label to ensure it is formulated to apply to vegetable gardens. These products work by adding an herbicide layer to the soil profile through which the emerging weeds cannot grow. Contrary to the thought that they prevent germination, they are applied mostly to pre-germinated weeds to prevent growth. The problem is that in most cases we cannot grow things in the garden from seed once a PRE is applied. Post-emergent (POST) applications of herbicides is possible in the garden. First, we can use things like the active ingredient glufosinate or glyphosate to kill weeds before we plant. This is a good idea, especially if there are a lot of perennial weeds present in the garden area. Both chemicals require a time period between application and planting, so make certain to read the label for that information.

We have some selective chemicals in the garden that can be used for annual and some perennial grass control. These contain the active ingredients clethodim or sethoxydim and they are sold under multiple tradenames such as Select or Poast.

Remember, no chemical is “Safe” they all have cautions and labels. Make certain to read the entire label of any chemical you intend to use in your home landscape, especially near your food.

If you are having trouble with growing in your home landscape, call the Extension office at (252)946-0111 or email me at Keep an eye on our website or the Beaufort County Master Gardener Facebook page for upcoming classes and events. Mark your calendars for our Totally Tomatoes class coming April 13 (registration required, only 4 tickets left) and our Extension Master Gardener Plant Sale April 20. We will have over 1,000 vegetable seedlings for sale from 9:00-11:00 or until supplies last. Until then, Happy Gardening!