Healthy soil is fundamental to the living world around us. It helps to ensure a successful harvest of the crops we eat, supports our forests and wildlife diversity, recycles nutrients and cleans our air and water.

This week, we learned about soil preparation that is underway for an upcoming Little Forest planting project in the Kingston area. Master Gardener Astrid Muschalla guided us through the process.

Soil Texture

Soil is composed of minerals, organic matter, gases (air) and liquids (water). Soil texture refers to the proportion of sand, silt and clay particles that make up the mineral portion of the soil. Sand is the largest and heaviest component (0.2-2mm diameter), silt is 0.002-.2 mm and the clay particles are the smallest and lightest fraction (less than 0.002 mm). Depending on the relative amounts of these, soil is classified into one of twelve types, such as loam, sandy clay, silt loam and so on according to the diagram below. 

USDA Soil Texture Triangle

Astrid described a simple sedimentation test that can be done at home to determine soil texture.

A soil sample should be taken at a depth of 15-20 cm from a representative area of the garden. Fill a straight sided jar (a mason jar works well) about a third full with your soil sample, and then add water until the jar is about 2/3 full. Add a teaspoon of dish detergent and then shake vigorously for 10-15 minutes.  Allow the contents to settle – this may take several hours to several days. The longer settling time is needed if the soil contains a large amount of very fine clay particles.

Image credit: ScienceDirect.com

The sand, silt and clay will be deposited in different layers which can be measured to determine proportions of each.  Once the percentage of each has been calculated, simply match the percentages of sand, silt and clay on the soil triangle diagram to determine soil type. Such soil testing revealed the Little Forest site to be “sandy loam”. Note that this test does not measure organic matter content.

Little Forests

There are four Little Forests being planned to start this fall by members of Little Forests Kingston, partnering with the Rideau 1000 Islands Master Gardeners. The plantings will be primarily deciduous trees, aligning with the mixedwood plains ecozone* of the Kingston area. 

Kingston area planned Little Forest sites

All are sited on lands currently covered by pasture grasses. The soil in these areas is dominated by bacteria, however, to support deciduous plantings, amendments will take place to encourage the growth of native fungal species. 

Soil Amendment

The existing grassland will initially be covered with a 10-15 cm layer of dry leaves (or old hay or straw), which supplies the carbon needed to support a fungal population. Leaves can be whole, but if oak or poplar are used, it is helpful to chop them to encourage more rapid decomposition. This layer will then be covered with a 2-3 cm layer of composted, not fresh, manure, as a source of nitrogen. 

Lastly, the area will be covered with a 10-15 cm layer of fresh deciduous wood chips. Ramial chipped wood (RCW) is ideal. These are chips made from small to medium sized tree branches, up to 7 cm in diameter. The composition of fresh RCW is higher in nutrients than that from larger tree limbs and trunks, and promotes the growth of soil fungi.

Ramial chipped wood. Image credit: nature-and-garden.com

Soil amendment will take place at planned Little Forest sites in the fall, to allow time for the materials to decompose over the winter months. Once planting begins, the root area of young saplings will be inoculated with mycorrhizal fungi, available commercially. 

Mycorrhizal fungi (mycorrhizae) are found naturally in the soil and form networks of filaments which are associated with roots, collecting water and nutrients for the plant. As was described in a recent blog, it is not necessary to apply supplemental mycorrhizae to most gardens, however, in areas with degraded soils, it may facilitate the growth of the mycorrhizae and thus support growing plants. 

Little Forest, Clifton, Karachi. Image credit: Afforestt

For more information about Little Forests, visit Rideau 1000 Islands Master Gardeners .

*Ecozones are areas where plants, animals, people, soils, water and climate interact to form distinct ecological systems.