Black plastic does not raise soil temperature as high as clear plastic and will not kill pathogens or fungi. But it can be more effective at killing weeds. Black plastic blocks the sunlight so that plants cannot produce sugars through photosynthesis.
Neither clear nor black plastic will eliminate every weed. Sturdy weeds can puncture the plastic and grow through either color. Heat- and drought-resistant perennial weeds or those with deep roots may be able to enter a dormant state and begin growing again once the plastic is removed.
Killing weeds with plastic will have different results depending on the color of the material. Clear plastic raises the temperature of the soil. This can kill weed seeds and roots as well as soil pathogens and fungi. It also allows light through the plastic, which can allow heat-tolerant or hardy weeds to survive. Clear plastic is most effective during the hottest summer months.
Crafting and creative projects have been part of Heidi Grover's life since she was old enough to reach the glue and glitter. Grover received a degree in creative writing from Utah Valley University and combines her love of crafting with her love of words.
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.
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.
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.”
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).
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.
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.
If there are shrubs and trees present, cut them down with an ax or chainsaw. The ground needs to be smooth before you begin soil solarization (since you will be spreading plastic over it), so you will also have to remove the stumps left behind. If you are looking for a cheap way, use a tool called a “mattock.” Dig and chop your way with the mattock under the root-ball to access and remove the taproot. Warning: this is hard work and may be feasible only for smaller stumps.