The Top Ten Weeds

As spring goes into full bloom, all things are growing lush again. The oaks are finally done dropping old leaves, and new green is everywhere. Unfortunately, this also means weeds are seeing new life. Because it’s time to get your yard ready for the coming summer, we thought it a good idea to assemble a guide to the most annoying weeds we deal with here at Wilmot Botanical Gardens. It’s probable that you fight them too.

Dirt is full of weed seeds. When a fellow plant lover offers you a plant for your yard, it’s wise to consider what else you’re receiving in that plant pot. Weed seeds can also be spread by birds. Birds eat the seeds, digest them, and then deposit them on your lawn and garden beds. Humans also spread weeds when seeds stick to our clothing or shoes and then travel to other locations.

We have not included pictures in this article due to space limitations, but here is a link to IFAS’s Gardening Solutions website, in which you can find most of these offenders—or type them into your search engine and look for images. In no particular order, here are the top ten weeds we struggle against in the gardens:

  1. Dollarweed or Pennywort (Hydrocotyle umbellata): This is a bane of every lawn lover. Given its name for its resemblance to silver dollars, Dollarweed is an aquatic weed. It loves water, so when it starts popping up in the yard, it means either we have received plentiful rain or we’ve been overwatering our lawns. It can also appear when there is standing water. Post-emergent herbicides that are safe for lawns will usually wipe it out for a time.
  2. Oxalis corniculata (Wood Sorrel) and Oxalis debilis: These weeds are mistaken for types of clover. We’ll start with corniculata: An aboveground creeping wood sorrel, this one has tiny yellow flowers and seed pods that, when mature, explode, proliferating seeds all around. Oxalis in general has clover-like leaves, but it is not in the clover family. While weeding for oxalis of every type, it helps to have a deep-digging weeding tool. Get beneath the plant and pry its roots out. Corniculata tends to have a very deep central root. Of course, on corniculata, be sure to pull its aboveground stolons wherever they have spread. Post-emergent herbicides usually do a fine job eradicating this plant.As for Oxalis debilis, this weed also has the deceptive—and even larger—clover-like, heart-shaped leaves, and there are three of them joined at the base of the “heart.” The purple-leafed version of this plant is actually sold as a decorative plant in some places. Oxalis debilis has a tiny purple flower, and the entire plant rises from a central bulb of sorts composed of many separate and smaller bulbs. On mature versions of debilis, you will usually find a clear root, like a clear carrot taproot at the bottommost portion of the plant. Post-emergent herbicides will usually kill it fairly well. If the top is pulled off the plant, it tends to scatter the bulb of amassed “seeds,” which readily come up individually. It can be quite hard to kill.
  3. Spanish Needles or Beggars Ticks (Bidens alba): You can see this Florida native weed growing at construction sites after a few weeks, after the dirt is stirred up. A constant survivor, Spanish Needle can rise to waist high or more. It likes either full sun or part shade. It has a small white flower with a yellow center. The state butterfly, the Zebra Longwing, uses this plant, among others, for food. Spanish Needles are self-pollinating, but they are also good for the pollinator population at large. Some gardeners have learned to live with it, for it is a surprisingly vigorous grower, insistent and abundant. It seems to have a 100-percent success rate for self-propagation as well. So far, no pre-emergent herbicide has been found to stop its march. Post-emergent herbicides, however, work very well. Or, you can simply pull it out of the ground. If it is a mature plant, you might want to use a shovel to do so. Be sure to get every single bit of root out of the ground, or it will quickly return.
  4. Common Vetch (Vicia sativa): Appearing in late winter/early spring, this lanky weed can add nitrogen to the ground as it decays. Its seeds look like miniature green bean pods, yet its mature size can make it an eyesore in a formal garden. Post-emergent herbicides will kill it, but it can become stringy and bushy enough that hand-pulling becomes the quicker option.
  5. Yellow Nutsedge (Cyperus esculentus): One of the most prolific weeds out there, yellow nutsedge,  will quickly flood your garden beds if not eliminated. Hand-pulling is the best option, as Round-Up usually won’t kill it. However, we have used Spectracide Weed Stop for Lawns that does kill it fairly well. Yellow Nutsedge, like Dollarweed, loves overwatering. This annoying grassy weed puts up one stand of grass, and then it shoots a rhizome underground and comes up nearby. If you have a weeding tool, get beneath each sprig and get it all out—especially the “nut” it from which it grows.
  6. Chamberbitter (Phyllanthus urinaria and Phyllanthus tenellus): This weed comes in two similar types. They both resemble perennial peanut or mimosa sprouts. The worrisome thing about Chamberbitter is that the underside of every little frond on the plant has a line of seeds just waiting to mature and drop. Post-emergent herbicides kill it well and are recommended because hand-pulling might take quite a bit of time if it has infiltrated your lawn.
  7. Asiatic Hawksbeard or Asiatic False Hawksbeard (Youngia japonica): Appearing from fall to spring, this broadleaf weed sends up one thin shoot from a basal rosette of broad leaves and can grow up to a foot high. It has tiny yellow flowers which quickly go to seed. Asiatic Hawksbeard has a fluffy seed pod like a tiny dandelion pod and will propagate with the wind.
  8. Florida Betony (Stachys Floridiana): Betony has square stems and is in the mint family. It spreads via underground rhizome from a white grub-like root, which is actually edible. Betony can spread like wildfire, so stopping it quickly should be priority. It responds well to post-emergent herbicides. If you hand-pull it, you must get the white root to eradicate it fully.
  9. Crabgrass (Digitaria ciliaris): This is an especially frustrating weed from spring through fall. By summer, it is mature and a ravenous grower. The trouble with crabgrass is that it spreads from the center and if not stopped, can take over entire areas of your lawn, even suppressing your lawn grass. The bigger it is, the more extensive its root system. If it grows too large, a shovel will be needed to remove it. At times we have pulled clumps of Crabgrass that are three feet across in neglected areas. That leaves a crater, so don’t let it get too large. Another warning: Pre-emergent herbicides work better than post-emergents.
  10. Basketgrass (Oplismenus burmannii): One of the most quickly spreading weeds at Wilmot Botanical Gardens, Basketgrass is nigh unstoppable. It can invade areas of your lawn and suppress the growth of your grass. The good news (or bad news) is that it likes shady areas. Once it gets into your lawn, hand-pulling is your only option; we have not found an herbicide yet that will affect it. If you spot it, eliminate it, or you will be dealing with it for a very long time. It is called Basketgrass because its leaves look like an alternating basket weave pattern. It has alternating pointy leaves, some of which can have a wrinkled appearance. Some varieties have purple tips. It spreads on stolons aboveground and can become a lawn all its own when allowed to spread. The only problem with giving up and letting it be your lawn is that it disappears in the winter. So if you let it have its way over your lawn and landscape, there will be a vast empty region from about December through April.

Stephen Pritchett