Blog about – Defeating weeds, nature’s way

Begin forwarded message:

From: “Native Plants Wildlife Gardens” <carolebrown>
Date: June 25, 2011 6:47:29 AM PDT
To: “Renee Roth” <rraeroth>
Subject: Native Plants and Wildlife Gardens – Defeating weeds, nature’s way


Defeating weeds, nature’s way
Have you ever enthusiastically dug out a new garden bed but then had the weeds explode out of control over the next few weeks? Believe it or not, the major cause of garden weed sprout is soil disturbance by the gardeners. Indeed, every time we pull a weed, we encourage more weeds. I do conservation area restoration, which can be looked on as a giant weed control job where we’re always looking for new ways more efficiently of controlling weeds. Wherever you weed, weed control starts with understanding the seed bank.

A curbside bed, dug up, mulched and then ignored; a few weeks later, it’s all weeds

SOIL DISTURBANCE AND THE SEED BANK

The seed bank consists of thousands of dormant seeds which are “deposited” in the soil via near-by plants, wind, water, animal droppings, foot traffic, and the like. The seed bank is continually being replenished by seeds from many sources. Once deposited, seeds stay alive in the soil for many years — 5 to 7 years is common and there are reports of spouting after decades. When the soil is disturbed by foot traffic, uprooting plants, digging holes or other cause, the seed bank is said to be opened. Exposing buried seeds to light even for a few seconds can trigger germination. While there can be seeds of desirable plants in the seed bank, unfortunately, many of the fastest sprouting seeds are those of undesirable plants that thrive in disturbed soil and that aggressively out-compete other plants.

Do your own experiment. Yes, pulling weeds is fast and provides immediate gratification. However, it is often counter-productive. Better methods are cutting, smothering with mulch, and, if need, be soil sterilization. Try it yourself: in part of your garden, cut, rather than pull, weeds for a month or so and see if you don’t have fewer weeds. Most weeds can be defeated by frequent cutting to ground level. The trick is to get out there on a weekly or biweekly basis before the weeds have time to regenerate.

Cutting tools: In conservation area restoration situations, my team does not use power equipment to cut invasive plants (our weeds) due to the impact on, say, near-by nesting birds, and the risk to native plants interspersed with the weeds. My team’s favorite cutting tools, by far, are Felco by-pass hand pruners. Scissors with a fairly long blade and hedge clippers are also popular. A folding pruning saw with 5″ to 7″ blade can be used like a machete for rough cutting through a large stand of tall weeds. For light garden work, there are scissors with a 36″ handle which allow ground cutting without the bending.

Hand cutting weeds with pruners

Other cutting methods: Cutting to the ground is cutting to the ground. Anything that kills the top of the plant without doing more harm than good can be used. In some situations, a mower or weed whacker is just fine. Some gardeners employ nontoxic vinegar sprays, steam machines, and, even, blow torches.

Long-rooted perennial weeds: There are some perennial weeds that spread via long rhizomes. These plants can not be defeated by pulling as each root fragment left in the ground starts a new plant. Repeated ground cutting is work but is often the only way to effectively remove the plant. These weeds also can be dug up if the soil is thoroughly sifted for root fragments, but then you’ll get new weeds from the soil disturbance. Where I live in Connecticut, invasive plants in this category include Japanese knotweed, phragmites, bindweed, and Artemisia (mugwort).

Large taproot plants: Plants with large taproots such as dandelions, dock, and plantain can be controlled with minimal soil disturbance by cutting the tap root just below ground level – this will defeat the plant much faster than above ground cutting.

Grass and wild onions: Grass, unfortunately, likes to be cut. In my area, gardens are also plagued with wild onions that don’t seem at all bothered by repeated ground cutting. These plants have to be (carefully) dug out; the grass can be smothered (see below).

Seedlings: Small seedlings can be gently hand pulled with minimal soil disturbance.

MULCHING

Mulch, to me, is the gardener’s best friend. A layer of mulch acts like skin for the earth, protecting it from moisture loss and disturbance. Further, most ground disturbance from the creation of new beds and from mixing in soil amendments can be avoided by leaving the digging tools in the garage and breaking out the mulch instead.

New garden bed – lay the bricks over turf; pour on the mulch; punch holes through the mulch and turf for the new plants; water.

Gardening with mulch: Usually, mulching three inches or more will smother existing plants and turf (but watch out for roots of near-by trees). It helps to ground-cut undesired plants before mulching. One inch of organic mulch applied annually is generally all the fertilizer even a vegetable garden needs. After mulching, sit back and let the ground critters break up the mulch and carry the nutrients down into the earth. When you must dig, an immediate application of mulch will help suppress weed sprout.

Mulching caveat: Know the source of your mulch. Non-sterile mulch can bring in weed seeds, including those of some very dangerous invasive plants such as kudzu and mile-a-minute. Further, some yard and garden compost can contain toxic residues from pesticides and the like. Accordingly, the best mulch is your own well-rotted leaf litter and compost. However, you don’t need to swear off other mulch, just be careful with it.

SOIL STERILIZATION

So why can’t we just routinely sterilize the soil by, for example, placing black plastic over a sunny patch of ground for a few weeks? Sterilizing the soil does help with the seeds, and weeds, already in the ground but not the new ones that naturally come in on a daily basis. Further, soil sterilization kills micro-organisms that keep the soil healthy and fertile. Sterilization, accordingly, should be considered a remedy of last resort for weeds that can’t be otherwise defeated.

© 2011 Sue Sweeney

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Defeating weeds, nature’s way

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