Get an early start on vegetable garden weed control
From Garden of Eden to Garden of Weedin’, gardeners have been dealing with weeds for centuries. Keep weeds under control early with methods such as mulch and herbicides.
May 3, 2013 - Author: Gary Heilig, Michigan State University Extension
Did you know that weeding takes more time than any other cultural practice in the vegetable and flower garden? I don’t know about you, but I don’t think pulling weeds is the best use of my valuable time.
If you are a procrastinating gardener, then you know what weeding is all about. In order to keep weeds under control, an early start and continual vigilance is necessary if you want to remain in control of your food production project, also known as the vegetable garden.
My favorite way to keep weed at bay is via mulching. Simply put, mulch is a covering and it can organic or natural. Examples include straw, pine needles or bark, cocoa hulls or shredded wood. Inorganic mulches include plastics, fabrics or re-cycled rubber. By covering the soil with mulch, seeds on or close to the surface will not receive enough light for germination, thus reducing weed growth. If mulch is thick enough, it can also smother germinating and small seedlings. Organic mulches such as straw will not prevent well-established or perennial grasses from growing up through the barrier, so those need to be removed before putting the mulch in place.
Mulches provide other benefits, too. The covering over the soil slows the rate of evaporation, thus preserving the available water for plant use. This is especially beneficial during dry weather. They also stabilize great fluctuations of moisture levels. This can reduce the level of blossom end rot on tomatoes.
Light-colored mulches such as straw reflect light, resulting in cooler soil temperatures. This is beneficial to plants that thrive under these conditions such as onions, carrots, cole crops and lettuce. Sometimes people will put down newspaper before adding the straw to reduce the amount needed. You can expect one large bale to cover 100 square feet.
Dark mulches such as black landscape fabrics or brown plastic warm the soil. Melon yields can be increased by about 50 percent when using them. Red plastic mulch has been shown to increase the quality of tomatoes while metalized plastic will repel certain insects such as aphids.
Once the season ends, organic mulches may be left in the garden to decompose. Adding some nitrogen and tilling will increase the rate of decomposition. Over time, this process will increase the level or organic matter in the soil, which will improve soil fertility, water holding capacity, increase the level of microbial activity, increase earthworm populations and so much more.
Another option is to use herbicides which are pesticides designed to kill weeds. An example of a pre-emergent herbicide, one that prevents weed seeds from germinating, is trifluralin (Preen). It can be used on a wide variety of vegetables. Depending on the crop, trifluralin can be applied before or after vegetable seedling emergence, but it will not control emerged weeds. It should be mixed into the top 1 to 2 inches of soil immediately after application, taking care not to damage any emerged crops. It should prevent weed growth for a month or more depending upon weather conditions. Repeat applications will be necessary for season-long control of many weeds.
A good, organic alternative is corn gluten meal (Concern). It has the added advantage of being 10 percent nitrogen, so it doubles as a fertilizer. There are several other organic formulations that are on the market, but few are available in local garden centers. Some examples include:
- WeedZap (45 percent clove oil + 45 percent cinnamon oil)
- Weed Pharm (20 percent acetic acid)
- GreenMatch (55 percent d-limonene)
- Matratec (50 percent clove oil)
- C-Cide (5 percent citric acid)
- GreenMatch EX (50 percent lemongrass oil)
These products kill on contact, but have no residual activity. They are most effective when sprayed on emerging weeds. Well-established perennial weeds will grow back quickly after treatment, so repeated applications will be necessary.
Perennial weeds can be controlled before planting by using glyphosate or covering the area for one to two months with a 6-millimeter thick, black plastic. I like to put the black plastic down in the fall and by spring the area under the plastic is clear of weeds.
If you begin the gardening season by keeping the weeds under control and you maintain your efforts before things get out of hand, your garden will reward you with abundant fruits.
If you have additional questions, contact your area Michigan State University Extension horticulture educator by calling 888-678-3464 or visit the Gardening in Michigan website and submit your questions to the Ask an Expert tool on the homepage.