By Kate Torpie, Garden Guides Contributor
Ambrosia artemisiifolia, or common ragweed, is a well-known villain to allergy sufferers; but sinuses aren't the only thing that ragweed damages. It can take over your entire garden, and crowd out your plants. Its leaves are deeply serrated, and rounded at the edges. The upper side of the leaves grow small hairs. Its dull-yellowish flowers grow in cylindrical stalks. From far away, it doesn't look too bad at all! There is another type of ragweed, called Giant Ragweed. The methods of control and growth requirements are the same for both. The differences are in appearance; giant ragweed can grow up to 16 feet. Its leaves are usually 3-lobed, with the same deep cuts and rounded edges.
Ragweed is an annual. It grows throughout the United States, preferring warm, sunny spots. It begins to grow in late spring, and lasts through late fall. Its spreads very rapidly due to the large number of seeds each plant produces. If ragweed begins to grow in a garden in spring, and goes untreated, it may be the only plant in your garden by the time summer ends.
Cultivation and Care
If you see young ragweed plants, you should water the soil and remove them by hand while the soil is moist, and the roots aren't as difficult to remove. You can also cultivate with a sharp hoe. Once the roots and leaves are chopped up, most young plants will die. Return after two days to pull any plants that started to grow. If you see adult plants (the mature plants have flowers), it's a good idea is to place a plastic bag over its head before removing. This will prevent the seeds from dispersing.
Weed Control Techniques
Herbicides containing clove oil, soap, and/or acetic acid work best. Be careful when spraying to avoid nearby plants. You should also be aware that repeated applications of acetic acid will lower the pH of the soil, and may affect the growth of nearby plants. Ragweed doesn't like humidity. A new technology offers the chance for time-released saline sprays that will keep the humidity level over 70 percent, and will keep the plant from growing. Soybean-based herbicides like FirstRate are effective work on broad-leaf weeds like ragweed, too. Studies have shown that applying to the plant while it is growing, for example, late spring, is more effective than trying to prevent the growth at all while spraying the soil. Basically, this product works best for controlling, and not preventing, ragweed.