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kill weed seeds in soil

Now use a steel rake on the area that you have just tilled, wielding it like a fine-toothed comb to remove the majority of the uprooted weeds. Next, rake the area again, this time with the object of evening out the soil as best you can and removing stones, twigs, etc. The final preparation for soil solarization will require the use of a garden hose. According to the University of Idaho Extension (UIE), you should moisten the area that you have just raked to “conduct and hold heat, to stimulate weed seed germination, and to prevent dormancy of below-ground vegetative plant parts.”

There is lots of work involved since soil solarization entails getting to the root of the problem, underground.   And we will not be taking the shortcut of using herbicides, so that means a bit more work. But if you do not mind getting your hands dirty, then let’s roll up our sleeves and begin stopping our weedy foes in their tracks.​

Preparation

Now you truly have a “clean slate” with which to work. Remove the plastic and lay down landscape fabric. You should try to use one of the stronger types of landscape fabric if possible, just in case—in spite of your best efforts—any sharp objects remain in the ground (which would puncture the landscape fabric).

Of course, if you use an organic mulch (such as a bark mulch), it will eventually decompose anyhow, becoming fertile ground for weeds. What can you do? Well, you had better keep new weeds pulled, faithfully. Vigorous roots pushing downwards can stress landscape fabric and breakthrough. On the bright side, these weeds should be relatively easy to pull, since mulch is a lot looser than dirt, and weed roots will not become impossibly entrenched.

Soil solarization is a preventive, organic method of killing weeds before weed seeds even sprout.   But the advice below is also meant for homeowners wishing to start a garden with a clean slate, reclaiming a patch of land where weeds have taken over, in such a way as to reduce to a minimum the hassle of future ​weed control. Want to transform a piece of land that has “gone to pot” into usable space? Then the method explained below may be the solution to your problems.

Some light passes through chunky mulches, and often you will discover—too late—that the mulch you used was laced with weed seeds. It’s important to replenish the mulch as needed to keep it about 2 inches deep (more than 3 inches deep can deprive soil of oxygen). In any case, you can set weeds way back by covering the soil’s surface with a light-blocking sheet of cardboard, newspaper, or biode­gradable fabric and then spreading prettier mulch over it.

You will need pruning loppers to take down towers of ragweed or poke, or you can step up to a string trimmer equipped with a blade attachment to cut prickly thistles or brambles down to nubs. No matter which method you choose, chopping down weeds before they go to seed will help keep them from spreading.

1. Let sleeping weeds lie

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I find fabric just gets in the way. The weeds will root on top of the soil regardless of whether fabric is down or not. I find a good layer of mulch, 3-4 inches thick, weeding by hand, making sure to get the roots, works best. Mulch will feed the plants as it breaks down, keep the bed cool, and retain moisture when it rains.

Does 32 ounces of vinegar mixed with 1/4 ounce of soap sound like an accurate mix

Now—that would also put a lot of Nitrogen into the soil, so I would then use that area to grow a non-fruiting, but Nitrogen-hungry crop like sweet corn , field corn, popcorn, salad greens, potatoes, onions or other things I’m not thinking of right now.

Anyway; next season, delay planting these areas until any missed weed seeds have germinated and been growing for two weeks. Then carefully and methodically slice them off at the soil line with a hoe that has a flat super-sharp blade, like a diamond hoe—creating what’s known as a ‘stale seed bed’. And whatever you do, don’t till the soil; tilling plants weed seeds!

So–what about those roots still in the ground?

A. Let’s start with the black plastic idea.

(Yes, the words ‘easily amused’ do come to mind; saves me a fortune on my cable bill.)

Because, as Kat discovered, yanking weeds that have already gone to seed spreads the seeds. When weeds are seedy, don’t pull right away. Instead use that flame weeder to incinerate the tops of the plants. Then run the flame up and down the sides of the plants; wherever you see seed pods. The torch will toast those seeds, and you can then pull out the plants without planting next year’s crop of weeds. Bonus: Many weed seeds look like Munchkin fireworks when they pop!

Wishful thinking. Weeds need no help surviving winter; and only clear plastic stretched tight over a perfectly prepared area for an entire summer can kill weed seeds. It’s called ‘soil solarization’, and this description of the proper technique is not my opinion; it’s the only way that diligent researchers got it to work. (Here’s the details in a very popular previous Q of the Week .)