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kill weed seeds in soil

Smother weeds and prevent new ones from growing by covering them with old newspapers. A thick layer of newspaper will keep sunlight from reaching weed seeds, so they can’t sprout. Wet the soil first, and then lay your newspaper down, wetting it thoroughly again before covering with mulch. This is a great way to recycle, and as a bonus, you’ll encourage earth worms to come and stay.

Cover your planting areas with mulch and you’ll keep weed seeds from coming into contact with the soil in the first place. Mulch will also keep sunlight from reaching seeds that are already underground, so they won’t get a chance to sprout. Mulch offers the added benefits of retaining moisture and breaking down to enrich your soil. And it looks really pretty, too.

Did you know that corn gluten meal is birth control for seeds? Sprinkle it on your garden and it will keep weed seeds from germinating and growing into plants. Of course, corn gluten meal will keep any seed from germinating, so don’t try this on your vegetable garden until your plants are established and you’ve finished planting seeds.

Newspaper

You can rid yourself of weeds the old fashioned way—pulling them by hand—if you’re vigilant. Wear a dedicated pair of gardening gloves for the task to avoid inadvertently transferring seeds elsewhere. Good gardening tools like a claw or sharp trowel can help you loosen the weed roots from the soil first. Pulling a weed completely out by the root is the only way to ensure it will not return.

Apply vinegar with a spray bottle, pump sprayer, or brush. Like other natural herbicides, vinegar cannot differentiate between weeds and other plants. Do this early in the morning, when there’s little wind, to avoid contaminating nearby plants. Vinegar’s killing properties are activated by the sun, so try this on a cloudless day, which also ensures that rain won’t wash it off before it works its magic.

Scald those pesky weeds with boiling water. Just grab your kettle off the stove and bring it to the garden. Pour a stream of water carefully on the crown of each unwanted plant. Tough perennial weeds with long tap roots may take two or three applications, but will eventually stop coming back. Use your hot pads, of course, and definitely take the precaution of wearing long pants and close-toed shoes.

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.

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.

Preparation

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.

Cover the raked, moistened area with a clear polyethylene sheet. The edges of the sheet can be held down by cinder blocks to keep the plastic from blowing away. If the raking mentioned above was done diligently enough, there will be no sharp objects sticking up to puncture the plastic. The sheet of clear plastic can be anything from 1 to 6 mil. in thickness. In the Northern hemisphere, the best time for soil solarization is June and July, when the sun is at its peak. UIE recommends keeping the sheet of clear plastic tightly stretched out over the area for about 2 months. During that time, the sun will be killing weeds for you—”cooking” them before they have a chance to sprout. Plant pathogens will be killed, to boot.

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.

“I began to measure weed seed predation and saw that within two days, nearly all of the seeds I’d put out in the field [to measure the amount of weed seed predation] would be gone,” says Davis, an ecologist with USDA’s Agricultural Research Service at the University of Illinois. “Over the course of a growing season, I’ve seen weed seed predators eat between 40% and 90% of the seeds produced that year. It’s an important weed management benefit that we take for granted, but which really makes a difference.”

Davis conducted that early research to evaluate a valuable option for growers who want to manage hard-to-control weed populations: Manage the weed seedbank to prevent weeds from getting started.

Weed management toolbox

Cover crops can be a tool for weed seedbank management. “Cover crops have had a long history in the Midwest, and can make a comeback should market forces and weed management realities combine to make them necessary,” Davis says. “Adding cover crops to the weed management toolkit can reduce opportunities for weed seedlings to establish, and can also provide a critical delay in weed seedling emergence so that crop competition can further suppress weeds.”

Davis says the most important element of a successful weed seedbank management strategy is to implement a diversified crop rotation so crops with contrasting life histories are grown in different phases of the rotation. “This prevents any one weed species from getting too comfortable, and makes it difficult for weeds to reproduce in the canopy of a crop with a different life history,” he says.

The key to weed seedbank management is to reduce the ability of the seeds to germinate. Then growers either don’t have the weeds to control or they have fewer weeds to handle with other weed management tools. Here are Davis’s suggestions for managing a seedbank: