While rain gardens are an excellent way to prevent the kind of pollution that is caused by stormwater run-off, they do come with some hidden pitfalls. A poorly designed rain garden can become a large mud puddle, a pool of standing water that breeds mosquitoes instead of putting rainwater to good use.
The answer to the problem is generally found in the soil. If the soil isn’t draining properly, the rain garden can’t do its job.
If you haven’t actually built your garden yet you can head this problem off at the pass. You can call the Natural Resources Conservation Service at (352) 338-9500. The NCRS can tell you how well your soil drains.
You can also do a simple drainage test. Dig a one foot hole. Fill it with water. Return to check the hole every four hours. It should drain an inch at a time every four hours. If it drains too fast or too slow then you may need some professional assistance to set up your rain garden.
What if you’ve already built your troublesome rain garden?
You may need to fix it by “amending” the soil. Amending the soil simply means that you’re going to add some new things to it to help it do a better job.
Low Impact Development suggests using the following amendments:
15% BY VOLUME DOUBLE SHREDDED HARDWOOD MULCH
50% BY VOLUME WASHED SHARP SAND – ASTML-33
30% BY VOLUME TOPSOIL
5% BY VOLUME PEATMOSS
The Virginia Department of Forestry recommends homeowners use:
50% sand, 25% topsoil and 25% compost or leaf litter (www.dof.virginia.gov).
It is important to note the sand used in a rain garden should ALWAYS be coarse, sharp sand. It should NEVER be contractor building sand. In areas of high summer soil heat, the compost or peat moss components will decompose rapidly. The double shredded hardwood mulch will decompose slower and will maintain the desired coarse and well-drained structure longer than some other amendments. In all cases, the quality of materials matters; topsoil should be weedfree and high in organic content and less than 10% clay.
Don’t give up on your rain garden if you are having trouble with it! You can fix most problems, and you can still have a rain garden that you can enjoy, even if it got off to a rocky start.
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