Crabgrass (Digitaria species) seedlings appear from mid-spring through summer in many types of soils. This fast-growing annual needs only warm rain to coax seeds to life. Where crabgrass infestation is severe, apply an organic corn gluten herbicide product in spring, keeping in mind that it will inhibit the growth of all types of newly germinated seeds. From late spring onward, pull young seedlings from moist soil, or cultivate when the soil is dry. Mulch to reduce seed germination, and space plants close together to crowd out seedlings that emerge late. Mow weedy areas near your garden to reduce reseeding. Flaming is sometimes used to control crabgrass in large gardens and fields.
Corn gluten herbicides. Powdered herbicides made from corn gluten keep crabgrass and other weed seeds from germinating and growing. They are typically spread on established lawns, but they also can be used in gardens where no seeds will be planted, such as in perennial beds. As the corn gluten degrades, it provides a small amount of nitrogen to the soil. Crabgrass begins to germinate at about the time that azaleas, dogwoods, and forsythias bloom, so spread corn gluten at that time for best results. Application procedures vary with the particular product; be sure to read and follow the directions on the label. Do not use corn gluten in newly seeded lawns, or in garden beds where you plan to sow seeds.
Pulling. Most young weeds can be pulled from the soil. They will slide out most easily if you pull them when the soil is wet. Getting the root up is crucial, so think of the main stem as the root's handle, and grasp it as close to the soil line as you can. If you find that the weeds are breaking off at the crown as you pull, slip a kitchen fork, dandelion weeder, or similar tool under the weed, and pry and twist as you pull it up. Weeds that have taproots, such as dandelion and plantain, usually must be pried out. A flexible pair of waterproof gloves will keep your hands comfortable as you weed, and it's good to have a nice sitting pad, too. Let pulled weeds bake in the sun for a day or so before composting them. If pulled weeds are holding mature seeds, compost them separately in a hot, moist pile before using this compost in the garden.
Cultivating. Slicing and dicing weeds with a hoe works best when the soil is relatively dry, and the same goes for cultivating with a tiller. With their tops mangled and roots cut, most young weeds will quickly shrivel up and die. Be careful to cultivate only the top inch or two of soil or you may injure nearby garden plant roots and drag new weed seeds to the surface. A sharp hoe works much better than a dull one, so refresh the edge on your hoe with a steel file between weeding sessions. After using either a hoe or tiller to cultivate weeds, go back the next day to nip out any survivors. When battling perennial weeds, you can weaken the plants by chopping them down with a sharp hoe, but it's best to combine hoeing with digging to achieve good control. Never use a tiller in soil that is infested with bindweed, quackgrass, or other weeds that regrow from small pieces of root; they are easily spread by rototilling.
Mulching. Mulch that's more than 2 inches thick can deprive most weed seeds of the light they need to germinate and grow. In vegetable and flower gardens, you can Mulch with wheat straw (which has fewer weed seeds than hay), chopped leaves, grass clippings, or many other organic materials. Where weeds are numerous, try covering the soil with four to six sheets of newspaper. Then cover the newspapers with 2 to 3 inches of organic Mulch. Pieces of scrap carpeting make a good weed-suppressing Mulch to use in pathways between rows. When Mulching beneath shrubs and trees, place a sheet of landscape fabric over the soil, then cover it with 3 inches of organic Mulch. An edging (a 4- to 6-inch-wide strip of rot-proof material driven into the ground vertically) of brick, stone, or metal will help the Mulch stay put, halt invasion by creeping weeds, and make the bed look neat and well groomed.
Crowding plants. When plants grow so close together that the ground between them is shaded, sun-seeking weeds, such as pigweed and purslane, don't have a chance. Use double rows rather than single ones whenever possible in your vegetable garden. In flower beds, place flowers in closely spaced groups. As plants need more room to grow, thin them gradually so weeds get only a fleeting chance at good light. Plants with broad leaves, such as squash and cabbage, do a good job of crowding out weeds. Vigorous lawn grasses that form a tight turf naturally crowd out weeds. To keep turf tight, apply a slow-release organic fertilizer during your lawn's most active season of new growth. The recommended cutting height varies with different species of grass, but with any type of grass it's a good weed-preventive strategy to mow high and often. Long blades of grass often do a good job of shading out germinating weed seeds.
Reducing reseeding. Most weeds reproduce primarily from seeds, and the seeds of some weeds can remain viable when buried in the soil for decades. So it's essential to keep weeds from shedding seeds in the garden. Garden weeds that are neglected until they reach seed-bearing age can be lopped off near the soil line with pruning shears, a stout knife, or a string trimmer with a blade attachment. Cutting back perennial weeds again and again not only reduces reseeding, it also forces the plants to use up food reserves stored in their roots. In a garden that has gone hopelessly weedy, mowing it down promptly, raking out the seed-bearing debris, and starting over next year is a big step in the right direction. Mowing regularly helps keep weeds under control in lawns. When mowing lawns where seed-bearing weeds are present, collect the clippings in a bagger and dispose of them in a shady place.
Flaming. Flamers are portable gas torches that produce heat intense enough to boil the water in plant cells. Killing a weed requires heat for only 1/10 of a second. Flamers are usually used to kill young weeds in prepared rows, just before seeds or seedlings are planted, as an alternative to pre-emergent herbicides. Flamers become trickier to use later, when the plants are actively growing, and they cannot be used where Mulches are present. flamers also are quite costly compared to a hoe, but may be a worthwhile investment if you have a number of straight rows to weed. They also are useful for killing weeds in between walkway pavers. The smallest models consist of a backpack that holds propane fuel, a hose, and a hooded nozzle at the end of a handle that resembles a carpet sweeper.Photo courtesy of Plant Stock Photos
Article published on June 23, 2008.