How to Implement Beautiful Mini-Swales and Save Vulnerable Soil

Swales planted with bare root plants.

How to Implement Beautiful Mini-Swales and Save Vulnerable Soil

A common question in landscaping is how to handle water runoff. Here in the midwest heavy rain is very common and can cause lots of soil erosion on unprotected slopes. In large, open fields, swales are a common permaculture solution to this problem. On our land, where we have small gaps in an otherwise closed canopy, we are using mini-swales to the same effect. Here, we tell you how to use this great landscaping tool on your property.

What are Swales

A swale is a shallow ditch that to improves rainwater infiltration and prevents erosion. Swales are built by digging a shallow trench, on contour, and mounding the excavated soil on the downhill side of the slope. A common practice is to plant swales with trees or shrubs. This helps with soil stability in the mound but also aids the growing plants by giving them access to the increased moisture captured by the swale.

In many cases swales are several feet wide and can be a few feet deep. The amount of rainwater in your area will determine the size of the swale you will need. Mini-swales are exactly like swales except smaller. Ours are only about a foot wide and 8 inches deep, for example. This smaller size means you can put the sales closer together. It also means you don’t have to have a large space to dedicate to the swales. Smaller swales means less space is required between the swales.

When to Use Swales

Unfortunately, swales are not “a one shoe fits all” solution. The main thing to be wary of is that swales can be dangerous on steep slopes. On a steep slope the extra water absorption can cause mudslides that destroy the slope and can cause damage to property as well as loss of life. Do not use any form of swale on land that has a slope exceeding 15 degrees.

As for when to use swales vs mini-swales this is a matter of what fits your space. As previously stated, in a large open area large swales are effective. In smaller spaces the large berms are a little less tractable. The size of your swale will depend on the size of the project. Where we needed to pack several swales into a small area, roughly 100′ x100′, that has poor soil, only 3″ of topsoil, swales were just too large to be effective. In situations similar to this, scale the swales down to a mini-swale and you will have better results. I have even heard of people using “micro-swales” in gardens. Scale the swale to meet the need.

Where to Put Your Mini-Swales

The first thing you need to do is determine where on your land you want to place your swale. This should be fairly straight forward, find a gradual slope that you want to improve. The improvements could include better water absorption, less erosion, improve soil by building topsoil, a desire to plant perennials, or a some combination thereof.

Once the site is selected you will need to locate your contour lines. A good place to start is by finding a contour map of your site. A contour map will give you an idea of how your swales can be shaped and their spacing.

Arial view of the swales.
An arial view of area we placed our swales in.

Next you will need a way to mark out the exact path of each swale on your land. We recommend using an A-frame level. They are easy to build and use. You will also want stakes or marker flags (we used utility marking flags). Starting at one end of a swale you will then walk the level down the swale, keeping it level at each step, and place a flag down to mark the contour line. Do this for each swale. Now that the swales are planned it is time to start digging.

What to Plant your in your Mini-Swales

Traditionally swales are tree growing systems. The large mounds of earth generated make ideal growth mediums for a trees early root development. In a mini-swale the earth mounds tend to be much smaller and as such do not accommodate large tree root systems. Trees can still be part of the mini-swales, they just won’t get the same benefits as from a larger swale.

A more ideal situation for a mini-swale is to plant on planting smaller perennials. Berry bushes and flowering shrubs are excellent candidates. We planted ours with a mix of a few small trees, lots of berry and medicinal shrubs, as well as support shrubs that fix nitrogen or produce bio-mass. While the exact plants you choose will depend on your environment and its needs here are some recommendations:

  • Include perennial food crops.
  • Mix in pollinator attractors.
  • Place nitrogen fixers around your other plants.
  • Try not to plant large groups of the same plant.
  • Make it pretty.
  • Plan a ground cover.

Once you have your swale planted all there is left to do is sit back and watch it transform your landscape into something new.

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