Is it OK to mix builders sand with compost and soil into my vegetable garden and into containers? I live in downtown toronto and have a small garden. The original soil in my garden was mostly clay but I have been working it over 15 years but am trying to get rid of more lawn for my garden.,
Working with clay soil requires much patience. The problem with clay is that the particles (aggregates) are small and fit together fairly tightly leaving very little space between for drainage or oxygen. Because of the lack of oxygen and drainage, the plants have difficulty absorbing nutrients and attaining the amount of oxygen they need to function properly.
The best supplements for clay soil is an increase in organic content. Compost, Leaf mulch, (mowed leaves in the fall), well rotted sheep manure and store bought mulch laid on top of the soil will slowly work its way down and start loosening up the clay. As you increase organic matter the worms will follow and oxygen and nutrients should over time become more available to plant roots
Amending clay soil with sand can be risky unless the sand is very sharp. Builder’s sand is sharp sand and is ground quartz and the particles are fairly large. But adding it to clay could end up creating a cement-like soil that resists root growth and hampers the flow of air and water. Therefore, it is not advisable.
Toronto Master Gardeners have two Garden Guides you might find helpful. The first from Fine Gardening deals with amending clau soils and the second with compacted clay soil. Look them up at:
https://www.torontomastergardeners.ca/index.php/askagardener/compacted-clay-soil/
For your containers, we recommend a Potting Mix which Contains No Soil (Dirt), a sterile mix which may contain a combination of sphagnum moss, perlite and vermiculite. Potting Mix has particles larger than soil to allow the flow of water and air in the container. Potting Mixes drain well while still retaining sufficient water for plants.
To add to the confusion some Potting Soils do have sphagnum moss, perlite and vermiculite added in. These potting soils may be okay for containers, but potting mix will give you better results.
Not all potting mixes are the same. There are different types for specific applications. An explanation of the differing contents can be found at the following website:
https://www.finegardening.com/potting-soil-ingredients