Natural Weed Control
By Kris Wetherbee | Mar 29, 2013
Believe it or not, weeds brought me great joy when I was a young child. My dad spent hours tending the yard and was always so relaxed — especially when weeding the garden and lawn. It was at those times that I would kneel down beside him to help. Knowing I had his undivided attention, I peppered him with questions, and, in the process of our bonding time, he taught me a lot about gardening and the nature of weeds.
My dad explained that the lawn and plants growing in our yard need the same things we all need for survival — food, water and sunlight — and that when weeds move in, they take away these life-giving essentials at the expense of the plants we want to grow. I learned weeds are often opportunistic in nature and can be pushy competitors. Getting a grip on weeds gives garden plants and the green turf the nutrients and space they need to perform their best.
In down-to-earth terms, a weed is considered a nuisance when it grows aggressively, reproduces with abandon, or easily displaces more desirable plants. Unwanted weeds not only compete with cultivated plants for water, sunlight, nutrients and space — compromising the health and beauty of garden plants — but the weeds themselves can be unsightly and disrupt the aesthetics of your overall landscape design.
The fact is, weeds are a continual presence, whether they pop up in lawns, ornamental plantings, beds and borders, vegetable patches or any opening they can find. We can’t eliminate every weed from the landscape, but we can learn to tolerate — even appreciate — a few random appearances, minimize the existence of others, and crack down on truly aggressive invaders.
When garden weeds do threaten a hostile takeover, you don’t need an onslaught of toxic chemicals to make them retreat. Many preventive measures and ecologically safe methods are available to help keep problematic weeds under control (identify the 10 most unwanted weeds in Photos Help With Weed Identification).
Develop a defense against weeds
Weeds are known for their ability to adapt to less-than-ideal conditions, which include soil compaction, erratic watering and improper cultivation. That said, a well-conceived garden plan and proper growing techniques are defense tactics that can help tip the balance in favor of the plants you desire.
One defense strategy is to set up your garden beds to nurture strong, healthy garden plants capable of competing with invasive weeds. In other words, zone in on garden plants when planting, watering and feeding, and not the weeds.
A good place to start is the soil, which should be rich in organic matter and nutrients. As a general rule, work a thick layer of organic matter into the top 6 to 8 inches of soil. Organic matter such as compost, dry grass clippings, aged manure, or shredded leaves and garden trimmings provides food for worms, fungi, and a host of other beneficial soil-dwelling creatures that break down the organic material, ultimately improving soil structure and recycling nutrients into a plant-friendly form.
Keep a light hand when working the soil, as rototilling or excessive cultivation can multiply weeds. Rototilling not only brings buried seeds to the top 1 to 2 inches of soil where most weed seeds germinate, it also greatly increases weed problems by chopping roots, rhizomes and stolons into tiny pieces that can regenerate new plants.
Another strategic maneuver is to water wisely. Overhead watering and sprinkler systems supply both weeds and plants with water. In contrast, drip irrigation and soaker hoses focus on the area they cover by delivering moisture right to the root zones of targeted garden plants rather than nearby weeds.
Cultivate a cover-up
One of the best ways to prevent weeds from gaining a foothold is to put into play a great cover-up. An easy way to do this is to grow plants close together. Close spacing creates a dense canopy of leaves that acts as a living mulch, shading the soil from sunlight so weed seeds are less likely to germinate. This can be achieved by spacing plants so their leaf tips touch each other when mature. Starting off with transplants rather than sowing seeds is another effective strategy because the leafy shade develops more quickly.
Mulching is a sometimes underused method when it comes to weed control. A 3- to 4-inch layer of mulch is quite effective at suppressing weeds by blanketing the soil surface, thereby preventing weed seeds from germinating and making their appearance above ground. The few seeds that do manage to surface are usually easily pulled.
For the most part, the best time to apply mulch is when your plants are just a few inches tall when growing by seeds; transplants can be mulched as soon as they are planted. Common sources for organic mulch include lawn clippings, shredded leaves, bark mulch, aged sawdust, wood chips, compost, nut or seed hulls, or even layers of newspaper or old carpeting not laden with chemicals.
Mulch applied over a synthetic barrier is even more effective at suppressing weeds than either one on its own. This dynamic duo is especially efficient at keeping many persistent perennial weeds under control. Thick plastic sheeting or landscape fabrics — available as spunbond, woven or non-woven materials — provide a great physical barrier to weeds. But unlike plastic, landscape fabrics usually last longer, plus they still allow water, air and nutrients to reach the soil.
The key to creating the ultimate cover-up from this powerful pair is to prepare the soil prior to planting, and then cover the ground with your synthetic barrier of choice. Be sure to make slits in the plastic or fabric to sow seeds or pop in plants, and top it off with a 1- to 2-inch layer of mulch.
Another weed barrier of sorts is soil solarization — an environmentally friendly, low-cost method of utilizing solar power to kill weed seeds before they germinate. Soil solarization works best when breaking new ground, establishing new beds, or where vegetables and other annuals are exclusively grown.
In soil solarization, the soil is cultivated to bring weed seeds to the point of germinating, then cooked so the seeds die as they sprout. This is accomplished by roto-tilling to bring weed seeds to the surface, watering the soil, then covering the area with a transparent polyethylene cover or clear plastic sheeting to trap solar energy. It typically takes from four to six weeks to get the job done.
Nip weeds in the bud
When weed prevention has slipped through the cracks — or too many weeds have grown through the cracks — it’s time to take action with a gloved hand or tools of the trade.
Hand weeding can be soothing to the soul, especially when you take your time to enjoy the sights and sounds of nature. You may even get an up close and personal view of birds in action. Towhees, juncos and other ground-scratching birds are especially at ease when we frequent the garden. (I’ve had juncos scratching the soil looking for insects to within six inches of my hand.)
Hand weeding is always easier and much more productive if you weed when the ground is moist. Many of the weeds I pull are by hand, but when I need reinforcements, I rely on the added assistance of a trowel, a hand fork, or a weed-pulling tool with a forked end to dig under roots — especially for perennial weeds.
Hoeing is an effective tool for dealing with young annual weeds and tiny, newly germinated seedlings. Surface hoeing is best when the ground is somewhat dry so any seedlings left on top of the soil are less likely to re-root. Some hoes slice just below the surface while other hoes — commonly called stirrup or scuffle hoes — scrape across the surface. Regardless of the type, hoeing is always much more productive if you keep the blade sharpened and follow up with repeated hoeing on annual weeds.
A shovel or mechanical weeder is the tool of choice for established weeds or weeds with persistent roots. Both tools are outfitted with long handles that allow you to stand while pulling out weeds, easing the burden on a bad back. The sharp tines or prongs on a mechanical weeder grip the weed, removing the plant and its roots — or at least, most of the roots — as you pull it out of the ground. A shovel or spading fork work best for perennials that spread, such as bindweed or Canada thistle. Just be careful to get as much of the roots and runners as possible. You may need to dig several feet away from the plant’s center in order to accomplish that goal.
When dealing with perennial, established or aggressive weeds, always remove them from beds and dispose in a hot compost pile — vegetative parts of many perennials can resprout if left on the soil surface. If your compost is less than hot, dispose of weeds that have gone to seed elsewhere. Feeding weeds to the chickens even turns them into fertilizer.
Recruit toxic traps
Some plants release natural toxins that inhibit the germination of seeds and growth of emerging seedlings. Known as allelopathy, this chemical warfare can be used to your advantage, especially in annual beds and vegetable gardens.
Sunflowers, sudangrass, rye, cucumbers, purple sage (Salvia leucophylla) and California white sage (Salvia apiana) are good weed-suppressing crops. Closely planted sunflowers, with their allelopathic tendencies, temporarily inhibit nitrogen-fixing bacteria in the soil. This is bad news for the germination and growth of any plant needing nitrogen. And weeds especially need ample nitrogen to germinate and grow; though some common garden vegetables, like corn, also require high nitrogen levels.
Corn gluten meal (CGM) is a protein-based, natural product that prevents root formation in germinating seeds. This nontoxic herbicide is more effective as a pre-emergent when incorporated into the soil than when used as a top dressing. Marketed under several names, such as Safe ‘N Simple and WOW, CGM is only effective when applied a few weeks before annual weed seeds germinate. Applications vary somewhat among the CGM products, so follow the instructions on the label for best results.
Target and destroy
From spraying to flaming, there are several tried and true methods that are designed to wipe out weeds.
Weed flamers are an excellent tool for weeding along fences, in cracks between pavers, in lawns, and around trees and shrubs. The scorching technique works by heating plant cells so they burst, causing the plant to die within a few hours. The heat is nonselective, with young plants being most susceptible. A single two- to three-second pass with the flamer usually kills broadleaf annuals; perennial weeds may require repeated treatments. Keep in mind that careless use can result in scorched trees, shrubs or even a fence. And never use a flamer in a bed covered with organic mulch.
Boiling water is an effective and inexpensive way of dealing with weeds. This works best with weeds that pop up between brick and pavers. Just be careful that you only scald the weeds, and not yourself.
Most herbicide sprays control both annual and perennial weeds, though best results are obtained when spraying weeds while young and actively growing.
Several nontoxic choices are available that you can buy or make yourself. Soap-based products destroy weeds with a killer combination of fatty acids and salts.
Some products, such as Weed Pharm, contain acetic acid. GreenMatch has d-limonene as its natural herbicide, and WeedZap utilizes clove oil (eugenol) and cinnamon oil. Repeated applications of straight vinegar also will lay weeds low, though the more you use, the more it will acidify the soil.
You may never win the war against weeds. However, with a good offense and a back-up defense plan in hand, you’ll be well-equipped to win the important battles, and then simply manage the rest.
Oregon-based Kris Wetherbee continues to fight the good fight against all types of weeds, and her gardens certainly benefit from her diligence.
Common Weeding Mistakes
Leaving bare soil uncovered. Whenever there is bare soil coupled with moderate soil temperatures, you have the makings for an invasion.
Using raw animal manure or hay. Hay and most animal manures contain weed seeds and should be thoroughly composted in a hot pile (160 degrees) before use. Horse manure is best avoided altogether.
Applying fertilizer improperly. When you fertilize the entire bed rather than the specific plant, you also feed neighboring weeds.
Pulling weeds and leaving them on the soil. Flowering annual weeds like purslane can continue to develop and dispense their seeds. Perennial weeds can easily re-root or grow new plants from pieces of root that break apart.
Delaying action. Don’t let annual weeds go to seed or allow perennial weeds to become established before dealing with them.
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