In the most recent Placer County Master Gardener newsletter, The Curious Gardener, Charlotte Germane (Nevada County Master Gardener) wrote an amazing article about how to deal with poor soil drainage. Click here to read the full article or continue on to see our shortened version.
If your soil does not drain quickly enough your plants can drown, which is why proper soil drainage is so important. One problem that can cause poor soil drainage is “layered soil.” All soil transitions from one layer to another but layered soil refers to abruptly changing soil layers which makes it hard for water to move through easily.
Check for poor grading, over-irrigation, and thatched lawns
Before you decide your soil is the issue, walk through your garden and evaluate the grading. It is possible that at some point in your yards history the soil was graded so the water drained towards an area with no easy outlet. Therefore if you unknowingly have started your garden in that spot, your soil will be holding too much water. If you have an automatic sprinkler system, measure the output at each station as you may accidentally be providing your plants with too much water.
Heavily thatched lawns will not absorb a reasonable amount of water as thatch builds up over time creating a barrier which water cannot penetrate.
Test your soil’s drainage
- Take your shovel, dig a hole one foot deep and fill the hole with water.
- Allow the water to drain completely and then refill.
- Measure the amount of water that drains in one hour.
If the amount of water that drains is less than two inches per hour, your soil has poor drainage. This could indicate your soil is clay soil which is great at holding on to water, so much so that it may not let the water drain away fast enough.
How to improve soil drainage
One major thing to understand is the difference between soil texture and soil structure. Soil texture refers to the proportions of sand, silt, and clay in the soil and cannot be altered, where as soil structure can be changed because it is how the particles in the soil aggregate.
- Add organic material- You can improve tilth by adding finished compost to the soil, which helps to create larger pores in the soil giving both air and water more room to pass through. Try adding 2-3 inches of finished compost to your beds and incorporate with a fork or shovel.
- Plant cover crops- Considered a traditional method for soil enrichment, crops such as vetch or clover are not grown to maturity, but are planted and then tilled or dug back into the soil before the seeds set. These crops improve soil drainage by breaking up the soil with their roots and by acting as “green manure” when they are plowed back in.
- Build a French drain- Moving water downhill is key to improving soil drainage, thus finding a downward slope in your garden is well worth the effort. If you have a flat yard consider creating a trench with a 1-3 percent gradual slope and filling the bottom with rocks to assist in moving the water away from the problem area.
- Dig or drill through a hardpan or clay pan layer- Hardpan can develop as a result of mining or construction activity. Hardpan less than two feet think can be double-dug during the dry season, then watered and allowed to settle. With hardpan over two feet think, you may need to do some deep ”ripping” or drilling.