Weeds are taking over the cracks in my driveway. What can I do?

Q: Our concrete driveway was poured with wooden spacers between the sections. Now the wood has rotted and weeds have taken over. How can I get rid of them?

A: Whether you have a driveway, patio or garden path paved with concrete, bricks or flagstones, you’re almost certain to be doing battle with weeds at some point. Although the narrow spaces between pieces of the paving don’t seem like an ideal place to grow, weeds seem to find what they need there. Yanking them out isn’t always easy. And they’re sure to come back. There are effective ways to keep the paving looking tidy, but the best solution really depends on the situation.

If weeds are just starting to show up in paving that is relatively new and weed-free, pulling the sprouts, roots and all, is feasible and effective. But if the tops break off, you need to extract the roots or the weeds are likely to regrow. And as that happens, many weeds also expand the number of root tentacles, making it much more difficult to pull the resprouted weeds. Most weeding tools can’t help you extract broken-off roots because the tools are too wide to reach down into the joints. Try using a painter’s tool, such as the Warner Paint Multi-Tool. Often called a 5-in-1 but sometimes designed and labeled to include more than five functions, this tool has a stiff but narrow blade and a point at one side of the blade that you can use as a mini pry bar to help lift stubborn roots.

Or you can use a tool designed specifically for cleaning out joints in garden paving. Some of these tools, such as the Crack Weeder, have a short handle, good if working on your knees eases stress on your back. Other crack weeders, such as the DeWit Patio Knife, have a long handle so you can work while standing up.

Pulling weeds is most effective when they are just getting started. It’s also the best (and only) option if you have plants you want to keep, such as thyme, growing between flagstones. On other paving, such as sections of concrete or brick, once weeds have grown into clumps, the fastest way to tidy up is to slice off the stems and leaves with a string trimmer. Direct the string so it whirls almost flat with the paving. Wear safety glasses in case the string flings grit toward your face. You can also slice off weeds by hand using a painter’s multi-tool (if the blade is sharp), or even a scraper with a razor blade.

Weeds you slice off are likely to regrow, though, so you will probably need to repeat the process at least a couple of times during the growing season. To lengthen the time between haircuts, some people recommend pouring vinegar or salt solutions into the cracks. But vinegar and salt, especially when used frequently, can degrade concrete, brick and some kinds of natural stone, and the runoff can affect roots of nearby plants. It’s safer to plan on whisking away the weeds periodically with a string trimmer.

There’s also the herbicide option, which is easy but carries health and environmental risks. And it won’t give you instant results, so it’s not something to try when you are rushing to prepare for guests. It’s safer to avoid spraying and pull or cut off the weeds.

To help keep new weed seeds from sprouting, if you have sand-filled joints between brick, pavers or flagstones, consider replacing the loose sand with polymeric sand, such as Techniseal EZ Sand. Polymeric sand comes as a dry mixture of sand and polymer. After you add it to the joints and sprinkle on water, following directions on the label, the polymer works as glue to bind the sand particles together. Besides helping to block weed seeds from sinking in and growing, the polymer also stabilizes the sand so it doesn’t wash out of joints. It also helps keep ants from tunneling through and carrying away the sand.

To replace the rotted wood in the joints between concrete slabs, you can add polyurethane caulk to seal the gaps and help prevent weeds. The joints need to be cleaned thoroughly beforehand — a pressure washer and a crack weeder would help with this — and allowed to dry. If the joints are wider than ½-inch, use a ropelike backer rod to fill the bottom of the gaps. Top the rod with caulk designed to bond to porous concrete, such as Sikaflex Concrete Fix No-Sag Concrete Crack Filler. A-1 Concrete Leveling, a company that specializes in lifting concrete slabs that have sunk or shifted, has instructions for applying the caulk on its website.