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killing weed seeds with clear plastic

When the lawn is dead, you have a few options. Clear away dead grass where you plan to put walkways or otherwise need an even surface. Where the lawn is to become planting bed, just treat the dead stuff as compost. Plant into or mound soil atop it. Eventually, it will disintegrate either way.

Why clear plastic is a must: I’m often asked if black plastic works as well as clear. The answer is a definite “NO!” It’s a matter of physics, but rather than give you a complex explanation, here’s an example from our everyday experiences that demonstrates the concept.

Solarization comes to us from the clever folks in Israel where resources are limited but demand is great.

After solarization

Since the plastic is clear, you can watch the lawn turn from green to yellow, then to straw brown. Once that happens, let the plastic sit another week or two, just to be sure.

This is the “greenhouse effect.” Clear glass and clear plastic trap the heating power of the sun’s rays. That’s why soil beneath clear plastic heats up more than soil beneath black plastic. Adding an air gap and a second layer of plastic heats the soil even more.

Summer is the best time of year to solarize. The air is warm, but more importantly, this is when the sun has its greatest heating potential. After six weeks or so, your lawn will be gone with a minimum investment of time, energy, money, and, best of all – no herbicides!

Now, have your car windows tinted. Repeat the process and compare the air inside the car to the air outside. What happens? Even though the surface of the car heats up the same both times, the inside of the car gets far hotter when its windows are clear (similar to clear plastic) than when they are tinted (similar to black plastic).

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).

When you cut slits in the landscape fabric and install new plants, be careful that you don’t get dirt all over the landscape fabric. After all, why prepare a home for airborne seeds? Sure, you will be applying mulch. But airborne weed seeds can wend their way through mulch particles. If they find dirt, then they are “weeds waiting to happen.”

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.

Preparation

First hack down the tall vegetation with a sickle, power trimmer, etc. But before doing so, make sure you know how to identify poison ivy, poison sumac, etc.

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.

Run a mower over the land to reduce the weeds’ height further. Now that all the weeds are as short as possible and the stumps have been removed, rent a large tiller to uproot all the weeds. Since this plot of ground is uncultivated soil, you will need a tiller that has some power: Do not undertake this task with a small garden cultivator! Allow the tiller’s tines to dig deep enough into the ground to loosen the weeds, so they can be removed—roots and all, if possible.

Perhaps you are wondering at this point, “Why do I need soil solarization? Why can’t I just lay landscape fabric at this point, punch some holes in it, plant my new plants and then cover with mulch?” Well, the reason you can’t is that your job of killing weeds has only just begun. Weed seeds that you can’t even see are lurking beneath the surface, just waiting to sprout. If the weeds are vigorous enough, they will find a way back to the light (remember, the integrity of the landscape fabric will be compromised when you punch holes in it for your new plants). So you need to kill those seeds before you proceed with laying landscape fabric. And that is a job for soil solarization.