In landscapes everywhere, weeds can pop up seemingly out of nowhere. In some cases these volunteers are welcome, but most of the time they're not. Where do they come from, and even more important, how do you get rid of these unwelcome visitors?
Lawn weeds come from a number of sources: carried in by the wind, deposited by birds, from mowers used by lawn-service companies, on a neighbor's shoe or even a pet's paws. Even if you routinely apply pre- and post-emergent herbicides, treating these weeds can be a never-ending battle. With so many methods of intrusion, it's important to remain diligent in removing these weeds as they appear throughout the year, especially before they have a chance to set seed and spread.
Weeds may also arrive in nursery containers and take over garden beds. "This is precisely how many of the most notorious weeds have been spread not just in this country, but throughout the world," says master gardener Paul James. Before you plant your new purchases, carefully inspect each pot to remove weeds, roots and all.
Soils, manures and compost also can harbor weeds. In even the best topsoil, seeds can lie dormant for months, waiting for the right conditions to germinate. Barnyard manures, especially those from grazing animals, are often loaded with weed seeds, which is why it's best to compost the manure for up to a year before using it. But even compost can harbor weed seeds. To prevent growth, routinely aerate your compost by turning it and make sure it stays relatively moist. Otherwise, it won't heat up enough to destroy weed seeds.
Certain mulches can contain weed seeds. "That's especially true of hay or straw, which is why I typically let the bales sit out for a year to rot, or break them open so that birds can devour the seeds," says James.
Packaged grass seed is prone to containing weed seeds as well. This percentage is noted on the bag, which makes it easy to select the product with the lowest percentage of weed seeds. Another seemingly unlikely source of weeds is rock. "I've been amazed at how many weeds have popped up in the rocks I brought in," says James. "In some cases they're actually somewhat attractive, but in all cases it's best to remove them immediately after they flower." Thistle, for example, pretty though it may be, is one that can quickly take over a property and is especially difficult to remove.
Vines are another scourge. Among the worst culprits are kudzu, poison ivy, poison oak, morning glory, bindweed and wild grapevine. These volunteers can grow undetected beneath the cover of landscape plants, only to vine their way up in search of sunlight, covering your plants in the process.
At this point, the vines can be tough to eliminate. Pulling the vine up, roots and all, is the best control method. If that's not possible, cut the vine near ground level and immediately apply an herbicide like horticultural-grade vinegar to the cut portion. In the case of poison ivy or poison oak, first put on a long-sleeved shirt and gloves. Then apply an herbicide to the leaves. When done, wash the shirt, gloves and yourself immediately.
Remember, many herbicides—including the most popular ones available on the market—are non-selective, meaning they'll destroy anything green: weeds, vines and a prized landscape plant. If the vine is intertwined within a landscape plant, try to pull the vine out of the plant if possible. Then carefully apply the herbicide only to the leaves of the vine with a sponge or paintbrush.
Volunteers of plants within our own landscapes can also pop up in other places. For example, Persicaria is a lovely plant, but it can spread like wildfire. Shortly after Persicaria blooms, make sure to remove the flower stalks so that seeds don't have a chance to travel elsewhere. "But despite my best efforts, I still find volunteers of this baby as much as 200 feet away from the mother plant," says James.
The same is true of several other popular perennials, shrubs and trees, like hackberries and redbuds. Pull them up while they're still young, or cut them back to the ground and apply an herbicide to the stems. You can also attempt to salvage the plant by potting it. The survival rate isn't great, but it may be worth a try for a free plant.