Ragweed (Ambrosia artemisiifolia L.) is a warm-weather annual that thrives in heavy, untilled soil. The presence of ragweed in a lawn or garden can cause hay fever and allergy symptoms, including a running nose, hacking cough, persistent sneezing and red, puffy eyes. You'll find around 17 species of ragweed in America, the most widespread being common ragweed (Ambrosia artemisiifolia), western ragweed (Ambrosia psilostachya) and giant ragweed (Ambrosia trifida). You can deploy mechanical, biological or chemical measures to control the growth of ragweed, enhance the look of the garden and alleviate allergy symptoms for people living in the vicinity.
Identify ragweed by its distinct leaves and flowers. Ragweed is an upright plant that grows up to 5 inches tall, depending on the species. The hairy stems range from green to purple and fruits resemble a queen’s crown. The leaves are around 6 inches long, hairy, fern-like and wider at the base than the tip. The flowers are yellow and grow in elongated clusters.
Pull ragweed by hand during mid-spring or early summer. Use a hand trowel to loosen the soil around weeds, and pull them out without risking injury to other plants’ roots. This is the easiest way to control weeds in a home garden or small area.
Cut the ragweed from the roots with a sharp-edged garden hoe. The ideal point to cut the weeds is approximately 1 or 2 centimeters below the ground level. This process kills seedlings even before they appear above the soil surface. Chop off fresh growth at regular intervals to eventually kill the ragweed plant. Hoeing also loosens the top layer of soil apart from improving air and water penetration.
Mow the area with a rotary mower to crush and kill ragweed. It is best to mow when the weeds are 2 centimeters above the ground level to reduce the seed bank and pollen count. Repeat this procedure once every two or three weeks to kill the fresh regrowth from roots and crowns left below the surface.
Apply a 2- to 3-inch layer of organic compost and grass clippings to block sunlight, moisture and warmth required by ragweed to germinate and grow. Thicker layers of organic mulches provide long-lasting weed control.
Cultivate open areas with a rototiller to control ragweed. A rototiller kills weeds and mixes them with soil to transform into humus after decay. Till at frequent intervals to prevent new growth of ragweed from crowns and roots.
Dilute a commercial broadleaf herbicide containing 2, 4-D as an active ingredient. Mix 1/4 pints of the herbicide with 3 gallons of water in a hand sprayer, and apply thoroughly to wet foliage. It is best to apply the herbicide in mid-spring or early summer and reapply after a month for killing larger ragweed plants. If you need to control ragweed in a small lawn, mix 2 teaspoons of glyphosate in 1 quart of water. Dip a sponge in the diluted herbicide, and wet the foliage of individual ragweed plants.