Rain Garden Technical Considerations

Youth Rain Action Storyboard

Rain Garden Technical Considerations

By: Cynthia Acuna


Testing the site: Type of soil

Finding out what type of soil is present at our site is important. The type of soil in the site will determine the depth of garden and the type of plants.

To test the kind of soil present, the simplest method uses a jar:

Dean Young from the TRCA holding a jar containing dirt from the site to separate the different soil types

Dean Young from the TRCA holding a jar containing dirt from the site to separate the different soil types

Obtain a jar put some soil from the site in it and fill it with water. Sand will sink to the bottom quite fast, leaving a clear layer to water. Silt will dust up and produce a heterogeneous solution. If the soil has clay, the clay will remain suspended at the top of the water. The behaviour of these sediments has to do with their size. While sand is the biggest of all and is made out of silica, it sinks to the bottom. A grain of silt is much smaller, therefore, it is easily disturbed and floats in solution. Clay, on the other hand, is much smaller, <0.002 mm, it does not easily absorb water and so floats at the top of water.


percolation test pit filled

Percolation test pic completely filled with water

percolation test pit_half water drained

Percolation test pit six days later, with only half of the water drained

On Friday July 13, a hole was dug. We were told that the people who were digging this hole were having a hard time and it did not all have to do with the intensely hot weather. The ground was very tough to break. This was the first clue that the soil had a large percentage of clay. The hole was then filled with water up to a certain mark. On Tuesday, July 19th, when we went to see the amount of water in the hole, we saw that only half the volume of water had drained! The clay had prevented the water from draining.

Clay soil and site: special considerations

The significance of a clay soil means that we need to have a rain garden that is not too deep, <30 cm. Instead of a deep garden, then, we will simply have to make it long. The space we ended up with was 20’ x 4’. The four feet from the curb, is due to the gas pipeline we encountered running parallel to the curb.

Planning and discussing

Native Garden Team working hard to design their garden

Native Garden Team working hard to design their garden

We were not discouraged with the restrictions set by the clay soil. The native plant group quickly got to work designing the garden on paper. We discussed where rocks would go and some of us were very quick to lay out a whole plan complete with paths and some consideration to the water requirements of plants. The exercise was a lot of fun because we were all discussing our plans and defending our ideas. It was great to collaborate with so many wonderful people that care so much about nature.

Visit the Youth Rain Action project page to learn more or contact Emily Dutton at edutton@ecosource.ca.

The Youth Rain Action Project is led by Ecosource in partnership with Toronto and Region Conservation Authority, the Burnhamthorpe Sustainable Neighbourhood Retrofit Action Plan (SNAP), and Sheridan Nurseries, and is generously supported by the Government of Ontario’s Great Lakes Guardian Community Fund.