Making a Swale

The ditch after I dug it out

Let’s get the question out of the way first. Maybe you are wondering, what is a swale? To answer this most simply: a swale is a mulch filled ditch. And now you are probably wondering, what on earth for? 

There’s some good reasons for having a swale. Where rain is scarce or erratic providing lots of water in part of a year but little or none in others, or in microclimates such as parts of a yard that are notably dry, a swale can help mitigate these conditions. In a heavy rainfall, water washes across the ground. Some will be absorbed by the soil, but in one hot, sunny day all or most of the moisture evaporates leaving the soil dry. Rushing water also can also carry away topsoil and valuable nutrients. 

A swale catches large amounts of water from spring snow melts and heavy rains. The compostable materials that fill the swale absorb the water like a sponge. Over weeks, and even months, the absorbed moisture gradually releases into the surrounding ground. Nearby plant roots then have a slow, steady supply of moisture. 

The usual and expected pile of rocks

A swale is  considered a useful strategy for the practice of permaculture. I first found out about them in Toby Hemenway’s excellent book, Gaia’s Garden. I was impressed to read that swales and additional water-holding strategies have turned small areas of desert into lush, green year round gardens. 

After reading about them I was curious to find out whether swales could be useful here. The only way to find out would be to actually construct one. So i made two. The first was made last fall above the blueberry patch. The patch is on a low slope and the blueberry bushes have always seemed a little bit too dry. I made this swale about 12 feet long. 

The newer one is shown in the photos, and was made this summer. It is at least twice as long and runs across the top of the fruit orchard. The orchard is on a hillside with a much steeper  slope than the blueberry patch and growing in sand and rocks and no soil, the trees at the top of the slope seemed to be drying out too much between rains. This area is out of reach of a hose, so a swale sounded like a good solution.  

Filling in with organic matter

Using a grubhoe and a shovel I made the ditch for this swale about a foot and a half deep by about two feet wide. In the design of a swale the downhill side of the ditch should be built up higher than ground level. This raised edge is called a berm. 

After admiring my new pile of stones (I’m sure a good use will be found for them), I got busy filling in the swale. Since we are in a forest there were plenty of materials all around. I started by dragging rotted logs and dropping them into the bottom of the ditch. Rotted logs are heavy being full of moisture already, and so I’m guessing they will be an ideal swale filler. These were followed by wheelbarrow loads of raked up leaves, dead branches, and other forest litter.

Figuring that the materials will pack down over time, I stacked them higher than ground level. To get them to pack sooner, I walked back and forth on it a few times. As a final touch i seeded the berm with leftover garden seeds. -jmm