Woodsorrel (Oxalis stricta) is a weedy wildflower that grows either as a perennial or a hardy annual throughout North America. This member of the shamrock family thrives in fertile flower beds, lawns, and in the shady nooks beneath shrubs. Plants grow 6 to 18 inches tall, and the leaves are edible yet sour. Small yellow flowers that close up in wet weather are followed by 1-inch-long green seedpods that point upward. Spray young seedlings with an organic herbicide containing clove oil, or simply pull plants before they produce mature seeds. Mulching also discourages woodsorrel.
Organic herbicides. There are several herbicides made from natural ingredients. Those that contain clove oil (eugenol) give the best control of young broadleaf weeds. Products containing acetic acid, often in combination with citric acid, do a good job on young grasses. Some products contain both clove oil and acetic acid, so they are useful for a broad variety of weeds. Soap-based herbicides dehydrate leaves by cutting through their protective layer of cutin. All of these types of organic herbicides work best on young weeds and pose only a temporary setback to well-rooted perennial weeds. To minimize damage to neighboring plants, spray only in dry, still weather. To maximize effectiveness, spray young weeds when temperatures are above 70 degrees F and the sun is shining brightly. Be aware that repeated applications of a product containing acetic acid (which is very strong vinegar) can lower the soil's pH, making it more acidic.
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.
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.Image courtesy of Jenna Antonino DiMare, National Gardening Association