A weed is any plant growing in the garden that you do not want. Weeds are pest plants.
Weeds steal water and nutrients from flowers, shrubs, and trees. Weeds compete with smaller plants such as annuals and perennials for sun. They often provide refuge for pests and diseases.
Most weed species are fast-growing and abundant re-seeders. Weeds—like flowers and vegetables—may be annuals, biennials, or perennials.
Annual weeds germinate, grow, and re-seed in one season. Biennial weeds germinate and grow foliage the first year; they flower and re-seed the second year. Perennial weeds live more than two years and commonly reproduce not only by seed but by roots, stems, and stolons.
Annual and biennial weeds are generally shallow-rooted and can be slowed if not allowed to flower and set seed. Perennial weeds are deep-rooted and can be especially difficult to be rid of, especially the older they get.
Weed Management Overview
Keeping the weed population to a minimum is important not only for overall garden appearance but also to ensure that ornamental plants–the plants you want in your garden–thrive.
Here are some global suggestions for dealing with weeds. These will be followed by specific weed controls actions:
• Weed tolerance. You will never rid your garden of all weeds. Decide how many weeds you can tolerate and how you can turn their presence to your advantage. Know the problem: What weed species are growing in your garden? (Identify them and make a list. Know their life cycles and habits.) How aggressive are they growing and spreading? Where are they growing? How much damage are they likely to cause other plants? After you answer these questions, you can begin to manage weeds, not let them manage you.
• Habitat modification. Weeds can be managed with the modification of the growing conditions which allow them to thrive—habitat modification. Where weeds thrive you can limit the availability of water, nutrients, and sunlight. You don’t have to nurture weeds; you can manage them.
• Irrigation. Drip irrigation or directed watering of ornamentals–annuals, perennials, shrubs, and trees–will eliminate the widespread availability of moisture to weeds. Avoid overhead watering which spreads moisture to all parts of the garden—not just where it is needed. Use a drip irrigation system that places water in the root zones of ornamentals and edibles. There will be little moisture left over for weeds.
• Fertilizers. The application of fertilizers or plant nutrients closely around ornamentals (an application called side-dressing) rather than across a garden bed will limit the nutrients available to weeds. Sidedress ornamentals plants with compost or fertilizers—place fertilizer close to crop roots and stems. Avoid using more nitrogen than necessary; many grassy weed species thrive on nitrogen.
• Sunlight. Limit sunlight available to weeds by closely planting annuals, perennials, and shrubs and covering unplanted soil with mulch. Vegetable gardeners call this kind of planting intensive planting; the method works for ornamentals as well as edibles. In an intensively planted flower bed, the leaves or ornamentals touch and shade out new weeds.
• Mulch. Weed seeds find it difficult to germinate if mulch keeps sunlight from reaching the soil. Apply light mulch such as aged compost or chopped leaves to 3 inches (7.5cm) deep.
• Focus. Focus your weeding efforts on weeds that exceed your tolerance level. Suppress weeds that threaten ornamentals or edibles and other cultivated plants rather than all of the weeds in the garden.
Weed Fighting Techniques
Here are some specific weed-fighting techniques:
• Remove weeds and their roots as soon as they appear. Pull weed seedlings by hand or chop them off just below the soil surface with a hoe. Use a garden knife or a screwdriver to upend deep-rooted weeds. Frequent weeding sessions will prevent weeds from becoming established.
• Smother weeds with a deep layer of organic mulch. This is most effective against weed seedlings. Use weed-free pine needles, straw, or dry grass clippings. The thicker the mulch the harder it will be or weeds to germinate and grow. Weeds that poke through mulch are easy to pull by hand.
• Use inorganic mulches. Weed fabric, newspaper, and cardboard also make excellent mulch. Cover these with decorative bark or aged compost for a natural look. Feed fabric which is made from spun poly comes in rolls and can be cut to fit planting beds; the fabric is kept in place by garden staples. Lay down four or five layers of newsprint or a thick layer of cardboard. (Use newspaper or cardboard that does not contain colored print or a wax coating.) Black plastic can be used to deprive weeds of sunlight and smother them as well, but plastic is best used in the cool time of the year so as not to overheat the soil during the growing season.
• Never let weeds flower. If weeds begin to flower, pick off the flowers immediately and dispose of them. Don’t let weed flowers form seeds. Place weed flowers and seed heads in the trash, not in the compost pile.
• Spray weeds with vinegar. The high acid content of vinegar (try pickling vinegar) will slow weeds. Several applications of vinegar may be needed to totally eradicate some weeds.
• Scald weeds with boiling water. This is effective against perennial weeds but may require several applications. After you apply a stream of scalding water to a weed, immediately cover it with newspaper or black plastic to be sure no light reaches the weed. The roots of many perennial weeds can survive a round or two of hot water and even herbicides–be persistent in your efforts to kill perennial weeds.
• Improve the soil. Many weeds thrive where the soil is organically imbalanced—low in some minerals and an excess of others. Add aged compost to planting beds regularly to keep the soil fertile, an even balance of major and minor nutrients necessary for plant growth. Be sure that you add only weed-seed-free compost to your garden beds.
• Avoid rototilling. Once planting beds are established, avoid rototilling or turning the soil any more than necessary. Weed seed can sit dormant deep in the soil for years just waiting for exposure to light and moisture. Rototilling can bring weed seed the soil surface where it can germinate. Sheet composting–adding a layer of compost across the planting beds twice a year—is the best way to feed the garden and avoid turning up buried weed seed.
• Study Integrated Weed Management (IWM). IWM is the holistic approach to weed growth and suppression in the garden. IWM recognizes that the complete eradication of all weeds from the garden now and for all time is not only impossible but probably not desirable.
Benefits of Some Weeds
Weeds can serve a purpose; here are benefits weeds offer:
• Soil fertility and water holding capacity. Perennial weeds such as thistles, nightshades, and pigweeds are deep-rooted and penetrate the subsoil. Root penetration breaks up the soil and allows water and nutrients to move up and down through the soil. Moisture seeps down and phosphorous and potassium are drawn to the surface for use by other plants.
• Habitat for beneficial insects. Weeds in the sunflower (Asteraceae), parsley (Apiaceae), and mustard (Cruciferae) families are nectar sources for beneficial insects. Most weed flowers are shallow throated making their pollen and nectar easily available to beneficial insects.
• Trap crops. A border or row of weeds along a garden will attract pest insects that otherwise might concentrate in the garden and harm ornamental and edible plants. You can encourage weeds that attract pest insects. Keep trap crop weeds lush and irrigated to attract insects, but cut back the top of weeds before they flower and set seed. Monitor weedy trap plants for insect eggs and pest insect larvae; handpick or spray pest insects in trap plants before they move into the garden.
• Soil protection. Low growing weeds that compete poorly with ornamental and edibles can protect the soil from drying out. As long as weeds are not competing with your garden plants for moisture and nutrients, they can hold the soil in place and keep the sun from baking the soil.
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