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Q: I have a brick path, and my friend has a brick patio. We get weeds growing between the bricks. Is there any way to prevent this? We use weed killer every three weeks. Is there something safer and more permanent? PP meltblown nonwoven
A: Weeds are weeds precisely because they grow where they’re not wanted. Varieties that need coddling don’t become weeds. Ones that do tend to be hardy and produce lots of seeds that spread easily, sprout well and grow fast with whatever moisture nature provides. That makes them tough to control.
Brick-paving installers sometimes spread nonwoven landscape fabric as a root barrier before they place bricks. But although this can keep weeds from growing up from underneath the bricks, it doesn’t stop weeds that send out stolons or rhizomes — runners that creep in from the edges of the paving. Nor can the fabric keep seeds that are blown onto the bricks by wind or a leaf blower from settling and sprouting in the crevices, which stay more moist than the bricks.
To keep brick paving weed-free, you can choose from several strategies: spraying with herbicides, blasting seedlings with a flamethrower or hand weeding. Following up on any of these by filling joints with polymeric sand can dramatically reduce the problem long-term.
Spraying with herbicides is quick and effective, but as you’ve discovered, it doesn’t last forever. And there’s a long history of pesticides that manufacturers claimed were safe but that later proved to be unsafe. If you’re okay with spraying herbicides but want to spray less often, you might consider changing what you use.
Are you using Roundup Ready-to-Use Weed & Grass Killer, probably the best-known product from this brand? Its active ingredient is glyphosate, which plants absorb through their leaves and stems, so it works only on plants that are actively growing. (Roundup also makes Weed & Grass Killer products with “Plus” or “Gel” added to the name; these are basically glyphosate but also contain an ingredient that make plants wither faster — important for customers who want to see the plants begin to die within a few hours, rather than a week.)
Because of how glyphosate is absorbed, the Weed & Grass Killer formulas have no residual effect on seeds that haven’t sprouted: Whenever there are new seeds and enough moisture, you’ll get more weeds. But Roundup Extended Control has ingredients that keep seeds from sprouting, and Roundup Concentrate Max Control 365 has enough of these ingredients to keep seeds from sprouting for a year. These products aren’t absorbed only by leaves; roots can absorb them, too. Do not use them if your paving is over the root zone of trees or shrubs or if runoff goes where you plan to plant within a year.
If you want to avoid herbicides, a flame-throwing wand and a propane tank is your best bet. Many garden stores sell these, as do home centers. Flamethrowers don’t work well on big weeds with thick tap roots, such as mature dandelions, but a quick pass usually wilts and kills small, young-looking weeds. For compact paving areas, you could use a torch that works with a one-pound propane cylinder, like you would use for camping. An example is the Flame King Propane Torch Weed Burner ($24.95 at Home Depot). For larger paving areas, get a torch that works with a 20-pound tank, like you would use for a backyard grill.
Hand weeding also works, without any of the worries about poisoning people, pets or soil, or affecting the climate by burning fossil fuel. It’s fairly easy to pluck out young weeds, roots and all, especially soon after a rainstorm. The hook end of a painter’s 5-in-1 tool can be very helpful in narrow gaps between bricks. But it’s nearly impossible to completely pull big weeds with thick taproots, such as mature dandelions, or established clumps of a runner-forming weed, such as Bermuda grass.
Whichever of these approaches you take, if you do get rid of the weeds, consider following up by filling joints with a mixture of fine sand and polymer — an ingredient that functions like glue to seal gaps between the sand particles so the joints become just as inhospitable to new seeds as the bricks themselves. The polymer also remains slightly flexible, so the filler holds together as the paving expands and contracts with shifts in temperatures and humidity or the pressure of foot traffic.
When polymeric sand is applied as a retrofit to existing brick paving, it’s often necessary to first scrape out whatever filler is between the pieces. If the gaps are empty, you will have very little prep work to do. Polymeric sand comes as a dry, premixed powder. Follow directions on the product, but in general: Pour it on dry brick and brush it into joints with a push broom until they are about ⅛ inch from being full. Tamp the bricks to settle the powder, then add more as needed. Lightly mist with water to activate the polymer. Let dry for the time recommended on the label.
A couple of cautions, though: Don’t fill joints with polymeric sand if the bricks are part of a previous paving system designed to let rainwater flow through the gaps into a gravel bed below. Polymeric sand would keep the water from flowing through. And check the specs before you buy to make sure the product is suitable given the joint width in your paving. The particle size varies, which is why, as examples, EZ Sand Polymeric Sand ($22.98 for a 40-pound pail at Home Depot) is suitable for joints ¼ to 1½ inches wide, while Accel Dust Preventing Paver Polymeric Sand ($21.98 for 40 lbs. at Lowe’s) is for joints ⅛ to ½ of an inch wide.
When brick paving has become heavily infested with weeds, polymeric sand probably isn’t an option unless you pull up the pieces, remove all of the roots, and redo the paving. Short of that, it’s often possible to tidy up the paving relatively quickly with a string trimmer, aimed so it slices off the weeds right where they poke out from the bricks. But, alas, this will need to be redone frequently. Weeds will be weeds, after all.
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