Grasses and weeds growing out of pavement cracks in sidewalks, driveways, and patios is a common annoyance. Sometimes it seems as though these unwanted plants grow even better in tiny pavement crevices than they do in the lawn and garden. This defies all logic since pavement surfaces are brutally hot and dry places where you might think that nothing could survive. But not only do these tenacious grasses and weeds survive, they alsoseem to positively thrive in this no man's land of blistering hot pavement.
Thanks to this genetic tenacity, grasses and broadleaf weeds that sprout up through the cracks in the pavement are very hard to control. It is easy enough to pluck the top off at pavement level or sever them with a string trimmer, but unless you extract or kill the entire root, the plant often simply sprouts up again.
The reality is that pavement weed control is an ongoing landscaping maintenance task for homeowners, but the work is easier if you have a variety of workable strategies to choose from.
When to Kill Pavement Weeds
You can stay on top of weed control by devoting a bit of time to the job each week. Many homeowners like to conclude weekly mowing or garden work with a few minutes spent plucking or killing the weeds sprouting out the pavement cracks around the landscape.
You will quickly recognize that various weeds have their favorite seasons, and are vulnerable to different control methods. The damp spring might be best suited to plucking weeds by hand, while during the dry months of late summer, chemical herbicides might be the better strategy.
Before Getting Started
Successful weed control begins with knowing your foe's likes and dislikes and habits. In their own way, weeds are marvels of genetic evolution. s
Driveway and sidewalk cracks turn out to be surprisingly friendly places for weeds. These cracks can hold a considerable amount of soil and organic matter, a perfect bed for grass and weed seeds, which are often very tiny. And just below the surface of the paving there is often trapped moisture, and any plant that sends its roots down below the slab has access to it.
Some grasses and weeds thrive in the heat. Crabgrass, for instance, is a warm-season annual grass that thrives in driveway and patio cracks. Its seeds are very tiny and can penetrate the smallest cracks. Quackgrass is even more diabolical because it is a perennial weed that can survive even if just small pieces of root remain beneath the slab. If the exposed portion of the grass is removed, a new shoot will pop up in no time at all.
In cold weather, a dark-colored asphalt driveway absorbs sunlight and keeps the soil beneath warmer than the surrounding landscape. Some grasses and weeds can easily tolerate the salts in ice-melt products. Fescue, for instance, is a cool-season grass that is somewhat salt-tolerant and might have a good chance of surviving through the winter in a driveway. Sedge is a grass relative that tends to stay green in winter. And then there are the cold-happy weeds such as chickweed that seem to scoff at temperatures at which other plants would have long disappeared.
In other words, the weeds and grasses that thrive in pavement cracks do so because they are genetically well adapted to the conditions created by concrete, brick, or asphalt paving. It will take repeated efforts using a variety of methods to control these invasive super plants.
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6 Ways to Kill Weeds in Pavement Cracks
Here are some common, effective ways to control the weeds and grasses that infiltrate the cracks in paved surfaces. If a recipe calls for salt, make sure to limit its use to hardscape areas only; do not allow the salt to run into lawns and gardens.
- Hand-picking: The time-honored method is still one of the best. By carefully pulling the weeds in a way that extract the entire plant, root and all, you will prevent the weed from resprouting. This method works better for some weeds than for others, but it will always be easiest after moisture from rainfall or a garden hose has softened the soil in the cracks and the underlying soil that is holding the roots. But it is not a permanent solution, as new weeds will certain find a foothold in the deserted cracks unless you make efforts to seal them with some type of patching compound or pavement caulk. Vacuum out the cracks first, then fill them with mortar or masonry caulk to seal them.
- Boiling water: If the unwanted grass is near the kitchen door, pour leftover boiling water from the stove on weeds rather than down the drain. Though many weeds like somewhat hot conditions, none will tolerate steaming water. Do not worry if there is salt in the water; salt helps kill many weeds. Make sure you do not use water that has oils or meat leftovers from cooking. After a few boiling water treatments, most broadleaf weeds and grasses give up.
- Kitchen vinegar concoction: A mixture of 1 cup salt (about 228 grams) and one gallon (about 3.8 liters) of white vinegar (5 percent acetic acid) spread on pavement will kill most weeds and grasses. To make it even more caustic, add 1 cup (about .28 liters) of lemon juice. To increase sticking power, add 2 tablespoons (about 28 grams) of dish soap. If you have it, pickling vinegar is more acidic than regular white vinegar and probably more effective.
- Propane torch: An ordinary propane torch can be used to burn weeds sprouting up through pavement cracks. Many weeds tolerate a fair amount of heat, but not the 2,000 degrees produced by a propane flame. Some manufacturers now offer long-handled weed torch tools specifically for this purpose.
- Horticultural vinegar: It may be hard to find in local stores, but it can be ordered online. This type of vinegar is 20 percent acetic acid. Mix it with some orange oil and a bit of phosphate-free dish soap. Acetic acid burns the plant's top growth, depriving it of the ability to photosynthesize. Make sure you use protection for your hands and eyes, it is acidic and can burn you.
- Non-selective weed killer: Chemicals should be a last resort, but if other methods fail, spot-treating grasses and weeds with a weed-killer containing glyphosate (such as Roundup) will kill the plant, roots and all. Any chemical product should be used carefully, but glyphosate does not linger in the environment the way the chemicals in some other weedkillers do. Other types of weedkillers may work on broadleaf weeds, but they will not kill grasses growing in pavement cracks.
Weeds often come back, especially perennial weeds with strong roots. And there may be lots of weed seeds waiting in the cracks for their chance to sprout. Weed control is an ongoing task, but a bit of regular weekly attention will keep your landscape looking pristine.