You know moss can be a problem when it shows up on your roof. It can also cause problems when it grows on an asphalt driveway. Do not ignore it. Depending on how much moss is growing on your driveway, you have options on how to remove it and keep it from coming back.
Moss thrives in humid climates, especially those that experience multiple days of heavy cloud cover in a row. Older asphalt driveways with pits and cracks are at increased risk for moss growth. The moss spores are blown into the holes and cracks, which collect water and soil and give the moss a good base on which to grow. If you have overhanging tree branches or a covered driveway so sunlight cannot directly reach the asphalt, the moss is more likely to flourish.
Moss on an asphalt driveway is a slip hazard. When it rains, it absorbs water and becomes very slick. If you walk over it, you can slide and fall. Moss will not damage your driveway on its own, but it can lead to damage. Seeds from other plants can fall into moss. When the seeds sprout, they will send out roots looking for soil and water. If those roots work their way into cracks in your driveway, over time they can cause the cracks to grow wider. This can make your driveway uneven and cause trip hazards when you walk across it.
If moss is growing in a small patch, pour a solution of one cup bleach in a gallon of water on it. Let the solution sit for half an hour, then brush away the moss with a broom. This kills the moss, but does not prevent it from returning. For a more extensive moss problem, create a copper sulphate solution. Add ¼ tsp of copper sulphate to 10 gallons of water. Soak the moss with the solution, then let it sit for 20 minutes. Wash the dead moss off your driveway with your hose. Brush away any stubborn patches with the broom. Copper sulphate provides some residual protection against future moss growth.
Copper sulphate can damage plants. When rinsing it off your driveway, direct the stream of water toward gravel or dirt rather than toward grass or shrubs. While the copper sulphate will protect your driveway for a little while, the protection is not permanent and moss will return. Removing overhanging branches so sunlight reaches your driveway will help keep moss away. Removing patches of moss as soon as you see them sprout keeps moss from becoming a serious problem.