Hi there, I am wondering if you would please shed light on how to obtain “horticultural grit” in Ontario. After listening to Monty Don’s oft-repeated advice to “add grit” to potting soils, I determined that in the UK, grit is defined as “Lime free washed granite angular grit”. I can’t seem to find this product for sale in Ontario, either online or in stores. What is an equivalent product available here that serves the same function? Does the chemical composition of the granite (as opposed to another type of stone) have something to do with its function, or is it just that its size and structure of the rock improves drainage in soil? Thank you !
Thank you for contacting the Toronto Master Gardeners.
Horticultural Grit is basically small stones of granite or quartzite. It comes in various sizes or grades for differing purposes in the garden. The purpose of using it are to improve soil structure and help with drainage, aeration, moisture retention, weed suppression, combatting erosion and adding weight to container soil, see examples below:
In heavy clay environments it can greatly improve aeration when added to the soil as the stones create pockets of air within the structure.
In sandy soils it improves drainage, lessening particle surface area and facilitating water movement within the soil.
In garden areas that tend to be wet, adding grit to the soil can reduce incidences of root rot and other diseases that like moist conditions.
In raised beds it helps with both aeration and drainage and in containers, it will also add weight to the potting soil so pots are less likely to topple over in windy conditions.
Grit gently dug in around plants will also help the soil in that area retain moisture, in the spaces between the stones, so that it is readily available for root uptake.
Top dressing with stones as a mulch reduces weeds and mitigates erosion where water runoff is an issue.
Most reputable garden centres, nurseries and hardware stores should carry a range of bagged stones/grit. The garden job at hand will determine the size or grade of stones you purchase, and onsite staff should be able to guide you with this. If you have difficulty with local sourcing, there are online retailers who will deliver for a fee.
Hope this information is helpful.