Effective Weed Control for Your Garden

Marc Montefusco
Frederick County Master Gardener Program

In the past, the U.S. government has recommended the use of napalm to eliminate pesky vegetation. Joking aside, weeds are a serious problem: as the not-so-proud owner of the National Champion Pokeweed, I ought to know. Like any serious problem - poverty, racism, Britney Spears - there is no easy solution. There are, however, ways to make things better (except for the Britney Spears part.)

Weeds are simply plants growing where we don't want them to. They spread the same way desirable plants spread: through seeds, by above-ground runners, and by underground roots. Let's look at seeds first.

Almost any garden soil contains a "bank" of weed seeds ready to germinate. If we provide those seeds with the light, water, and nutrients they need, they'll germinate and grow. Sometimes the very process of turning or tilling the soil exposes new weed seeds to light and moisture. Watch newly turned soil for germinating weeds, and slice them off with a hoe as soon they appear. Eventually, the seed bank will run out, and maintenance will become easier.

Weed seeds also blow or drift into gardens. Keep a close watch on wild areas of your yard to make sure that weeds don't go to seed. Regular mowing helps prevent dandelions and other pests, including unwanted grasses, from reproducing themselves. In some cases, a thorough eradication program is necessary to remove the source of the invading seed armies - we'll talk about some chemical options later on. Mulch, useful for so many reasons, also helps prevent seed germination.

Weeds like false strawberry (correct name?) and many brambles spread by runners that take root and create new plants. These weeds knit themselves so tightly into the garden that the only way to get rid of them is to pull them out by hand. Make sure the roots come with the tops, or the problem will continue. (This is true for most weeds.) That brings us to the question of soil preparation. A fertile, healthy, soil with good "tilth" - the horticultural word for proper soil texture - makes a great growing medium for weeds as well as garden plants. There's no way around that fact. The good news is that it's much easier to pull weeds out of healthy soil than it is to remove them from hard, compacted, unhealthy soil.

Weeds that spread underground are my least favorite. Bindweed and thistle are the two worst offenders in my garden, and they are very difficult to get rid of. Both have similar thick underground roots that spread parallel to the surface. You can physically remove the roots, but if you leave even a small piece, they will regenerate. If you remove the tops of these plants often enough, they will eventually weaken and die, but they are very persistent. I use one chemical trick with thistle that works pretty well (see below), but if bindweed has mingled itself through your valuable plants, hand-pulling is the only answer I know of. Don't let either of these menaces go to flower, by the way.

We haven't talked about herbicides (unless you count napalm, or for all I know, Britney Spears). There are basically three kinds of plant-killing chemicals: non-selective, which kill any and all plants on contact; selective, which kill only certain kinds of plants on contact; and pre-emergent, which prevent seeds from germinating.

Glyphosate, sold commercially under the name Roundup (among others), is an example of a non-selective herbicide. Glyphosate is considered by many authorities to be more "environmentally friendly" than alternative products, but there is a great deal of controversy regarding its effect on humans and the environment. With this and with any herbicide, follow the label instructions and cautions exactly. Glyphosate will kill most plants within a few days, generally breaks down within two weeks after application, and does not tend to migrate into the soil. 

Remember: Glyphosate will kill or damage any plant whose leaves or green stems it contacts. Here's a way to eliminate deep-rooted, established perennial weeds that have come up in the middle of a bed and can't be sprayed: cut the stem and apply a single drop or two of undiluted Glyphosate (I use a recycled nasal applicator. Label it carefully!). This will kill even persistent thistle, burdock, pokeweed and small trees, is economical, and doesn't endanger surrounding plants. Wear protective gloves during this process and wash up thoroughly!

2-4D, the active ingredient in most "weed and feed" products, is an example of a selective herbicide, acting only on broad leaf (dicotyledenous) plants, which is why it can be used on grass lawns and corn fields (grasses are monocots, and corn is a kind of grass.) "Drift" from this or any herbicide can lead to unintentional damage to nearby plants. In some cases, this damage mimics fungal or other disease symptoms. Many formulations are granular, which means you must use a carefully-calibrated spreader to apply them. If you spray, do so on still days, and once again, read and follow the instructions.

Pre-emergent herbicides won't substantially harm existing plants, but they make it difficult or impossible for germinating seeds to grow, in some cases by preventing new root growth. Pre-emergents will only work if you have already removed all the adult weeds in the area you want to protect. You must also make sure that the plants you want to keep are well-established, especially if you want to treat a newly-seeded lawn. The pre-emergents will kill young grass plants just as effectively as they do anything else.

A quick review of weed control methods, in order of both time and preference:

  1. Prepare your soil well - weeds will be easier to remove.
  2. Remove sources of weed seeds, and keep potential weed beds mowed.
  3. Mulch - not only does it conserve moisture and add organic material to your soil, but it prevents weeds from germinating.
  4. Hand pull or dig weeds from established beds or plantings, and be sure to remove the roots.
  5. Use appropriate herbicides only when necessary and only as directed.

Save that napalm for your family picnic, and good luck!

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