Got dandelions? Here’s what to do now to wrangle weeds
You can aim for lawn perfection, or you can go the route of having a “biodiverse” lawn and allow a few weeds to co-exist with turf.
Either way, it’s good to know what’s growing in your lawn and make decisions about how, or if, to deal with them. Here’s a look at some common weeds you’ll likely encounter soon:
• Dandelion ( Taraxacum officinale) sports bright yellow flower heads in May and June, followed by feathery, spherical seedheads. A member of the aster family, dandelions are deep tap-rooted perennials that form a rosette of toothed basal leaves. The seeds are wind borne and germinate easily.
Dandelion isn’t picky about where it will grow, even pushing between the cracks in pavement, but is most happy in a well- tended and fertilized lawn. Prior to the invention of lawns, dandelions were praised for their food and medicinal value and were introduced to America for these traits. Their roots aerate the ground, loosen hard packed soil and pull calcium from deep below, making it available to other plants.
Sometime in the last century, dandelions were judged as weeds. They are hard to eradicate and any small bit of root that is missed regenerates. Spot weed with a gardening knife to get as much root as possible. This will greatly reduce the number of dandelions in your yard. If you have a large infestation, try a “weed and feed” product. Remember to always follow the label instructions exactly.
• Ground ivy ( Glechomahederacea), also known as creeping Charlie and Gill-over-the-ground, is a perennial with square stems that root at the nodes and form dense patches. The round leaves have scalloped edges and smell minty when bruised. The flowers are purple five-lobed tubes that look a bit like a miniature orchid. It prefers shady areas. Ground ivy is shallow rooted and is easy to pull by hand. Weed and feed products also work on it.
• White clover ( Trifolium repens) is a perennial that forms a low creeping mat of three-lobed leaves and round white flower heads. The stems are prostrate and anywhere a node touches the ground, it will root. White clover prefers a clay soil, typical of our suburban yards. Close mowing doesn’t control its spread and it seeds prolifically. You may want to consider leaving it mixed with turf as its flowers attract bees.
If you desire eradication, consider both pre- and post-emergent herbicides. Pre-emergent weed controls, sometime called preventers, work to keep weed seeds from germinating and developing. Post-emergent weed controls fight weeds that have already germinated and emerged from the soil.
• Yellow sorrel ( Oxalis stricta) has leaves shaped like white clover, but is distinguished by its yellow flowers. It grows from interlocking rhizomes that easily break when trying to pull it up by hand. The rhizomes then produce bulblets that quickly grow a new plant. The plant also has a fibrous root system as a secondary source of nutrition. Cold weather will cut sorrel back to the ground, leaving bare spots, but the roots will survive. The best control is a preemergent application in early spring.
• Common purslane ( Portulaca oleracea) is an annual introduced from southern Europe and first reported here in 1672. It is a prolific seed producer. The stems and leaves are prostrate and store enough reserves to produce seeds even after being uprooted. Stem
fragments may also root and produce more plants. The succulent leaves are green above and pale purple below. Small yellow stalkless flowers open on sunny mornings. Seeds are produced 712 days after the flower opens.
According to Penn State Extension: “In established lawns, common purslane populations can be reduced by improving turf density through fertilization, regular mowing and the use of turfgrasses well-adapted to site conditions.” If you choose to use herbicides, pre- or post-emergent formulas will do the trick.
Mowing is the most important factor in lawn appearance and longevity. Maintaining a lawn height close to 3 inches helps stimulate root growth and shade out unwanted weeds. Sharp, properly adjusted mower blades provide a clean, even cut that heals quickly.
No more than one-third of the grass blade should be removed at each mowing. This means you may need to mow more than once a week during peak spring growth and rainy periods.
If your lawn is primarily a space for recreation, routine mowing will allow the surface to function in that way without the use of chemicals. For eradication of large colonies of common lawn weeds, herbicides are the most effective option.
Dianne Machesney is a Penn State Master Gardener, a volunteer program that supports the outreach mission of Penn State Extension. Extension provides research-based information on best practices in sustainable horticulture and environmental stewardship. For more information, contact the Penn State Extension of Allegheny County at alleghenymg@psu.edu or 412-482-3476.