Horticultural sand is an ingredient in some recipes for seed-starting mixes, commonly mixed with peat and perlite. However, it can be challenging to find in some regions, and when it is available, it's often expensive and sold in smaller quantities than what may be convenient for you. If you can't find horticultural sand at local stores, look for sharp sand, horticultural grit, or grit. You can also substitute it with coarse builders' sand.
Why Use Horticultural Sand
For all intents and purposes, horticultural sand is the same thing as sharp sand and is similar to builders' sand and horticultural grit.
These sands aren't the same, and regional variations abound, but they all can be used for the same purpose: to improve drainage, particularly in clay-like soil. In a seedling or potting mix, gritty sand does more than promote drainage, improving the soil's structure, providing tiny spaces for air and water to move around, and making it easier for roots to grow through the medium.
The part that makes it "horticultural" or suitable for gardening is that it is lime-free, so it will not adversely affect the pH balance of the soil. Horticultural sand should improve the soil. Another benefit of using it in the garden is that it's non-clumping, unlike other sand types. Since it won't clump, the soil shouldn't get compacted.
Also, consider horticultural sand as a good companion for clay soils. Mix it with clay to improve drainage and avoid compaction and aeration problems.
Horticultural Sand vs. Builders' Sand
Builders' sand is used in construction and is generally coarser and less uniform than horticultural sand or play sand. It can also contain impurities like rocks, clay, or other debris. Builders' sand is cheaper than horticultural sand and may have salt and lime, affecting plant growth and soil quality.
What's Mixed Into Horticultural Sand?
Horticultural grit and sharp sand are made from crushed rock like limestone or granite. Different types of stone have different pH levels, so try to find out what type of stone is used in the grit or sand to help gauge how acidic or alkaline it is. Builders' sand also comes from rock, but the supplier will unlikely know its origin.
Prices for these materials may depend on availability in your area, but builders' sand is most likely to be the cheapest, followed by sharp sand.
Horticultural Sand vs. Other Sands
The most commonly available gritty or coarse sand is builders' sand because it's a common building material. It's used in concrete mixes and some mortar mixes. Builders' sand is not the same as play sand or sandbox sand, which are made of finer, rounder grains, similar to beach sand. Mixing fine sand into your starter mix will turn it into cement. It won't drain well, creating the reverse of the desired effect.
Coarse builders' sand is sold in the masonry department of big home centers and through masonry and landscaping materials suppliers. It has a much larger and coarser grain than play sand, making it perfect for drainage.
According to American Lung Association, builders' sand contains silica, a lung irritant. So if you're working with a lot of sand, wear a fine dust mask or N95 respirator.
Alternatives to Horticultural Sand
If you can't find the appropriate sand, you can always try a different seed starting mix that doesn't require you to use horticultural sand.
Ensure the recipe includes something for drainage, such as perlite or vermiculite. Perlite is a volcanic rock similar to pumice that holds air well, aiding drainage. Vermiculite is an absorbent material that holds water but keeps the water out of the soil allowing for more aeration and preventing compaction.
You could also simply swap the horticultural sand for finished compost or vermicompost, which offers the added benefit of introducing rich nutrients into what might be an otherwise inert mix. Finished compost has gone through the entire breakdown process, looks and feels like dark, crumbly soil, and no longer looks like its original ingredients. It should have an unobtrusive earthy smell.
Many soilless seed starting mixes don't use horticultural sand, and drainage isn't a problem. So, if you can't source it, substitute it.
Silicosis. American Lung Association.