How to Keep Herbs Out of the Herb Garden: Gardening Q&A with George Weigel


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Hand pulling and planting close together are two effective ways to rid herb gardens of weeds.

(Susan Weigel)

Question: My wife and I have an herb garden, and year after year the grass seems to find its way into and around herbaceous plants. It takes meticulous work to keep pulling the grass. Is there a chemical you can recommend that we can use this year that won’t harm the weeds (or us) and kill the weed?

A: Yes, there are chemical herbicides that are labeled for use on most vegetables and will kill most grass weeds without killing your weeds.

The questions are: a.) Despite the labeling, are you comfortable using them around the plants you are going to eat? and b.) can you get them in the first place?

The first problem concerns your general philosophy on chemicals.

Some gardeners can use most products just fine, as long as the manufacturer tells them it’s OK.

Others take a more “safe than sorry” approach – especially in the edible garden – or have doubts by the time they’re finished reading all of the warnings and precautions on the label (assuming they read the label first).

Me? I am in the second camp. I’d rather not risk overlooking a potentially problematic label detail, and I’m still skeptical as so many “safe” chemicals used in the past are now banned when later evidence has uncovered problems.

I prefer to stick to mechanical weed control – pulling, planting the plants I want close enough that there is no room for weeds, and mulching the bare soil to discourage new ones. weed seeds.

If you want to try weed killers that are selective for grass and approved for vegetables, two that I know of are sethoxydim (Poast) and clethodim (SelectMax).

These aren’t readily available at garden centers as they are primarily intended for large commercial applicators, but you can get your hands on just about any garden chemical without restriction online these days. (For more on this whole box of worms, see my garden column on “Online sales of pesticides raise new concerns. “)

Another chemical option is to use kill-all herbicides such as glyphosate (Roundup) or pelargonic acid (Scythe). These are also labeled for use about many edibles, but keep in mind that they will kill just about any plant if you let the spray drift onto the foliage. Vinegar (acetic acid) is an “organic” option.

With any of these three, you will need to spray very carefully to target only the grass leaves and not the weeds.

A third chemical game plan is to treat the bed with a weedkiller. They are granular products that can prevent the germination of many / most new weeds. They do nothing for existing weeds but can slow down new germination if you time them correctly and continue to apply them two to three times a year.

Trifluralin, DCPA, and pendimethalin are three examples of weedkillers labeled for use around some edible.

Corn gluten meal is an “organic” weedkiller made from a corn by-product. Weed control is not as effective as with synthetic chemical weedkillers, but some organic gardeners use it and also like the fact that it also provides a dose of nitrogen fertilizer.

I highly recommend reading the labels of any of the above products carefully before purchasing and using them.

The University of Tennessee extension has a good line chart this will give you the basics on herbicides labeled for use on edibles.

If you are avoiding the chemical approach, try to “outsmart” the weeds. It starts with figuring out what kind of weed you’re getting and where it’s coming from.

Some weed grasses are “annual” (those that grow from seed each spring and die off each fall, i.e. crabgrass), and some are “perennial” (those that return year after year from their roots. and spread via runners).

Annuals are much easier to remove and can be stopped by mulch, which suffocates the soil enough to prevent new weed seeds from germinating.

If you can keep an inch or two of bark or leaf mulch on any bare soil in your herb garden, you should have a better chance of combating them this year.

Perennial grasses are much harder. They can wrap around your grass roots and run around the garden with abandon.

Since they’re winter hardy, they’ll come back year after year – usually stronger and ready to spread even further.

Some of them are even strong enough to send shoots through an inch or two of mulch.

Weedkillers are useless against these, so you’re looking to dig up perennial weeds or spray them with a herbicide.

If you dig, you need to get all the roots and runners, otherwise the pieces left behind will grow into new weeds. This is probably what is happening to you.

If you are persistent enough, you can win the battle by shooting, digging, pulling and digging more. Eventually you will get all the lumps, then a new layer of mulch should limit further germination.

For grass grasses intertwined with herbaceous plants, you may need to dig up the herbaceous plant to remove all the weed, then replant the grass. It’s a lot of work, but probably less in the long run than constantly pulling the heads of weeds out, to sprout new ones.

Keep in mind that most lawn grasses are perennials and can sneak into a garden. Once it invades the perimeter of the garden, its runners like loose, rich soil. Then your “lawn grass” turns into an aggressive “weed grass”.

The way to prevent this from happening is to regularly border your flower beds or cover them with stone or brick edging to prevent “lawn creep” from occurring.

I would skip it weed cloth that you might find on rolls in stores. It is not very effective in the long run and may slow down the growth of your herbs.

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Terri S. Tomasini