The heat from the water will cause the plants to start to wilt immediately, and will kill the roots over the following days or weeks. Boiling water is a great option because it easily gets into the cracks and doesn’t leave harmful residue in the soil. This method is generally most effective on young weeds. [2] X Research source
Repeat this process every few weeks as needed until the weeds have died and stopped sprouting. The salt and dish soap solution can discolor and erode cement and kill the surrounding plants. For a quick and easy option, sprinkle rock salt or table salt on the weeds to kill them. This is less effective for stubborn weeds, though. [4] X Research source
Most regular white vinegar is about 5% acetic acid and will get the job done. However, for stubborn weeds, you may need to get horticultural vinegar that’s 20% acetic acid. Horticultural vinegar is available at most gardening stores. Adding a quarter-sized squirt of dish soap to the vinegar may make it more effective. [6] X Research source
Borax can irritate your skin, so you may want to wear gloves when handling the solution.
Apply baking soda in the spring and fall to new, young weeds for the best results.
If the weed killer you’re using contains chemicals that are harmful to humans, wear protective glasses, long-sleeves, and gloves to protect your skin and eyes from exposure. [10] X Research source It takes about 2 weeks for commercial liquid weed killers to kill off the weeds.
You may need to apply heat to the area a few times to ensure that the roots are dead and won’t re-sprout. [12] X Research source Flame-weeders are available online and at many garden supply stores. You can also use an ordinary propane torch. Avoid using a flame-weeder near flammable materials like wooden decking or dry grass.
Operating instructions may vary, so make sure you read them carefully before using your weed steamer. The leaves will start to wilt and die immediately, but it generally takes 1-2 days for the entire plant to die. [14] X Research source You can also use a home steam-cleaning machine in the same manner. [15] X Research source
It may be helpful to spray the cracks with a hose or pressure washer to loosen the dirt and make the weeds easier to scrape out. [17] X Research source
Foam caulking backer rods are bendable and come in a variety of sizes at most home improvement stores, so you should be able to find a size that will fit in the cement cracks. Some large gaps in concrete are left on purpose to allow the concrete to expand and contract as needed to prevent cracking. The foam allows the concrete to continue to contract while filling the gap to prevent weeds from growing.
You can also use epoxy or blacktop filler instead of roofing cement to seal the cracks. However, blacktop filler may not be as durable in the long run as roofing cement or epoxy. [21] X Research source
The roofing cement or epoxy will likely dry on the surface within 24 hours, but may take 72 hours to completely cure.
Because sand and gravel can come loose over time, you may need to repack the gaps and cracks periodically to keep them filled.
