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Reader Question: Substitute for Horticultural Sand in Seed Mixes

By April 15, 2011

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James asked, via email:

"I am starting to prepare soil in a flat to grow seedlings. I was advised that a good mix is 1/3 peat, 1/3 perlite, and 1/3 horticultural sand. Horticultural sand seems difficult to obtain except in a small 2 quart box. (And it's rather pricey.) Is there a substitute for horticultural sand? I understand the sand should have sharp edges so that it drains well."

There are a couple of ways to answer this. The first is that you could try a different seed starting mix that doesn't require you to use horticultural sand. You are already getting good drainage in the mix thanks to the perlite in the recipe. James could just swap the horticultural sand for finished compost or vermicompost and get some nutrients into this otherwise fairly inert mix while still having good drainage. My seed starting mix doesn't use horticultural sand, and it drains very well.

If you're set on using horticultural sand or something close, look for "coarse builder's sand." Note: NOT play sand or sandbox sand -- these will just turn your mix into cement. They're way too fine for our purposes. Coarse builder's sand is often found in the masonry department of most home centers, where you'd find bags of cement and things like that. It has a much larger grain than play sand -- perfect for drainage. We've used it in both seed starting mixes and potting soil here at our house, and it works great. You could also try vermiculite, but between coarse builders sand and vermiculite, I prefer the builder's sand -- less dusty and it's super cheap.

I hope this helps. I'm always happy to answer questions -- drop me a line at organicgardening.guide@about.com.


April 25, 2011 at 12:35 pm
(1) Sandra Goth says:

I just wanted to say that you can buy Coir instead of peat. The harvesting of Peat Moss is destroying moss in forests and peat bogs world wide. Coir is made from harvested coconuts which are commercially produced. It comes in compressed blocks, expands when soaked and helps with water conservation, tilth and releases nutrients and is a sustainable resource.

May 3, 2011 at 11:35 am
(2) Rajeanne says:

Be very careful of what you buy. Coir is very harmful to pets…and it can kill a dog if eaten!!!

June 7, 2011 at 8:07 am
(3) Donna says:

I just bought some of this coarse builder’s sand, and it says on the bag that it contains a chemical known to cause cancer. It warns not to inhale it… Well, that won’t work! I am not sticking my hands in it, nor using it to grow plants. :(

June 7, 2011 at 9:38 am
(4) organicgardening says:

Coarse builder’s sand is an ATTRA-approved ingredient for organic potting and seed starting mixes, and does not contain any carcinogens. There are sands that are used for laying pavers that contain polymers to lock the pavers in place — these should be avoided — they will not work well in a potting soil mix anyway, and we definitely want to avoid carcinogens in our gardens. Here is the ATTRA site for anyone who’d like to read more: https://attra.ncat.org/attra-pub/potmix.html

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