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 How to Control Weeds
Our Water - Our World Fact Sheet (www.ourwaterourworld.org)
It is unrealistic to think that we can have a garden or a lawn that is entirely weed free. We need to manage weeds so they don't become an overwhelming problem. This means tolerating some weeds in some situations. If you really want to solve your weed problem, you will need to spend some time, have some patience, and expend some effort.
What is a Weed
A weed in the garden is usually a plant growing in the wrong place. This includes not only plants we normally think of as weeds, such as the dandelion, but also the tens of tomato seedlings coming up in the worm compost we've spread on a flower bed.
Invasives
There are, however, a number of nonnative plants that are very serious pests. When these plants are introduced into natural areas, they overwhelm native vegetation and degrade the environment for wildlife and humans alike. The worst of these invasive plants are classified as noxious weeds, and the government spends millions of dollars every year to remove them.
Some commonly available garden plants are actually invasive weeds that can "escape" from our gardens into wildlands. Don't use these plants and remove any from your yard.
Weeds Can Be Beneficial, Too
Deep-rooted weeds such as thistles, pigweeds, and nightshades can bring up minerals from the subsoil that are then deposited in the topsoil when the plants die and decompose. Deep roots can open pathways for water and for roots of less aggressive plants. Weeds in the sunflower (Asteraceae), parsley (Apiaceae), and mustard (Cruciferae) families produce flowers that feed beneficial insects with their nectar and pollen.
Non-Chemical Strategies for Controlling Weeds
To solve your weed problems in the long run, you must make the habitat in which weeds are growing inhospitable to them. In general, weeds prefer bare soil with lots of light; therefore, keep the soil in between your plants covered with mulch that excludes light from the soil. Patch cracks in paving, or fill cracks with special caulking compounds designed for asphalt or concrete.
It is very important to prevent weeds from going to seed. If you can reduce the number of weed seeds in and around your garden, you have won half the battle.
Hand Weeding
Weeds are easiest to pull when they are fairly small and when the soil is moist, but not wet. There are a number of useful weeding tools for sale, and gloves will protect your hands. Any weeds you pull up (or cut off) can be used as mulch around desired plants or can be composted, as long as they have not yet flowered and are not the kind that reproduce from plant fragments, tubers, or bulbs. Once weeds flower, there is a danger that seeds will mature on the plants even after they are pulled.
With established perennial weeds, concentrate on digging up the roots or depriving them of energy. If you cannot dig up the roots, cut the plant down to the ground. Cover the area with thick mulch, and if plants send up new shoots, cut them down again. Don't allow the plants to flower, produce new leaves, or go to seed. With no leaves to produce energy, the roots will eventually use up their reserves and be unable to produce new shoots.
Water Management
Prevent weeds from growing by keeping the soil too dry to support plants. Drip irrigation systems with drip emitters deliver water only to desirable plants.
Mulching
A thick layer of mulch deprives weeds and their seeds of light. Organic mulches, such as compost, leaves, sawdust, straw, newspapers, and cardboard, have the added benefit of providing organic matter for soil organisms to feed on. Weed control fabric and black plastic will also exclude light from weeds and their seeds. It is important to understand that mulches only prevent weeds that are under them from growing. Most organic mulches provide a good growing medium for weed seeds that blow in on top of the mulch, but you can more easily pull weeds growing in mulch than in soil. Weeds will also grow on top of weed fabric or plastic once enough soil or organic matter has accumulated.
The particle size of the mulch will determine the depth of the application. Apply coarse-textured mulches, such as bark and wood chips, 4" deep for weed control. Apply fine-textured mulches, such as shredded leaves or dry grass clippings, about 2" deep. Keep all mulches several inches away from the stems of plants or the trunks of trees and shrubs to prevent disease.
Weed control fabric, black plastic, or layers of cardboard and newspapers are excellent for large areas with very vigorous weeds. Place drip emitters in a 12" grid on the soil under newspaper and cardboard mulch to provide water to the roots of any desirable plants in the area and to hasten the decomposition of the weeds under the mulch. Cover these "sheet" mulches with wood chips or another organic mulch.
Use sawdust mulch only where you don't want anything to grow (e.g., in a pathway) because decomposing sawdust temporarily depletes nitrogen from the soil surface and makes it hard for plants to survive.
All organic mulches deteriorate over time, some more rapidly than others. Be sure to replenish them as they decompose.
Competitive Planting
Vigorous ground covers and plants with dense foliage can shade the ground enough that weed seeds have difficulty germinating. Lawns that are cut high will be able to shade out most weeds. When you remove weeds from a lawn, sprinkle some grass seed in the spot so that lawn rather than weeds will fill the hole.
Cultivation
Cultivation is using a tool, like a shovel, hoe, or roto-tiller, to turn the soil or remove weeds. Cultivation can bring new weed seeds to the surface, disrupt the food web of soil organisms, and ruin soil structure, so use this technique sparingly.
Mowing
Mow weeds or cut them with a weedwhacker before they produce flowers or go to seed.
Less-Toxic Herbicides
Products containing pelargonic acid (Quick Weed Killer) or soap (Concern's Fast Acting Weed Killer) will kill the above ground portions of weeds, but will leave roots that may re-sprout. Plants will be most susceptible when they are young. To kill older annual weeds or tough perennials, you will most likely have to repeat the herbicide application a number of times.
Caution: When spraying any kind of herbicide, protect desired plants from coming into contact with the spray. Do not spray on windy days. Prevent people and pets from having access to the area until the material has dried.
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