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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Wednesday - September 26, 2007

From: Denton, TX
Region: Southwest
Topic: Non-Natives, Edible Plants
Title: Weed prevention in vegetable gardens
Answered by: Barbara Medford

QUESTION:

Mr.Smarty Plants - I know this isn't your area, but we have a vegetable garden that has been plagued by summertime weeds. Do you have a recommendation for a control plan we could implement during the dormant time, fall/winter to ensure fewer weeds next year? Thank you.

ANSWER:

Weeds are usually native plants that are not what you wanted to grow there. At the Lady Bird Johnson Wildflower Center we very much support the protection and propagation of native plants, but not ALL native plants are equal, we understand that. However, the fact that they are native means they are going to want to flourish in the lovely soil you have prepared and watered for them, and their seeds are readily available in the ground or in the air for their continuation. Also, being native, they're going to be pretty stiff competition for the vegetables you intended to grow.

For starts, let us discourage your using any sort of herbicide or soil sterilizer. That is almost bound to end up hurting your vegetable crop, and you don't really want to eat anything that has come out of chemically altered soil, do you? Now, having said that, let us refer you to an excellent North Carolina State University site on "Weed Control in Vegetable Gardens." It does, at the end, discuss herbicides, but it also puts plenty of warnings about their use which it would be well to heed. One very interesting point the article made had to do with the height of the vegetables shading out the weed seeds. It even has a chart listing which vegetables are good for that and which are not.

You're right, vegetable gardening is not usually a subject dealt with by Mr. Smarty Plants, but we can perhaps provide a couple of personally-tried attempts to control weeds without chemicals. Almost everyone mentions mulches as a weed prevention tool. This does NOT include mulches like straw or hay, as they are likely to have more weed seeds than were in the ground to begin with. We have tried the method of spreading newspapers on the levelled soil, covering it with a good layer of organic mulch like hardwood bark, making sure it stays moist, and letting that shade out the weed seeds that might sprout early. This works the most effectively if you do it as soon as your vegetable garden is ready to be put to bed for the winter. The advantages of this are that both the newspaper and the mulch will slowly decompose and improve the texture of the soil. The reality of it is, the newspaper seldom decomposes within a season, and can quickly be left bare by the mulch blowing or being washed off. However, if you're willing to keep after it and maintain good coverage, you will at least have a start on a weedless garden. When you get ready to plant the vegetables, of course, you must remove newspapers and mulch at least from the row or area where vegetable seeds will go in, as they, just like the weed seeds, would be suppressed by being covered with no light getting to them. At that point, you might want to remove the remaining newspaper scraps, for looks if no other reason. Continuing to keep mulch between the rows of vegetables will continue to help with weed control and hold moisture in the soil. Once vegetables are well up, mulch can be spread around them.

We have also seen, but not tried, black plastic with mulch on it; same purpose, to keep light off possibly sprouting weeds. This isn't attractive, the plastic will not decompose, and it has to be removed before you begin to plant. And the landscape fabrics that will let water through to the soil beneath are also porous enough to permit the sprouting of weeds.

Final chapter, you knew this was coming. The best weed prevention is constant vigilance. Get them out, not just of the garden, but around it, before they go to seed. Any plant, including weeds, is much easier to get rid of when it's very small. Waiting until it's big enough to be yanked out means it may yank out some vegetable roots nearby. Tilling the soil may be necessary for the vegetables, but it sure turns up a lot of weed seeds. Weeds, persistent varmints, will still come up through mulches, including newspaper, that's from personal experience. Get them while they're young and vulnerable, and maybe they won't overwhelm your vegetables while THEY are young and vulnerable.

 

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