Gardening · Homesteading · Urban Homesteading

Make Your Own Seed Starting Mix

As Winter works its way through, the thought of starting seeds is on our minds. Whether you start seeds inside under grow lights or in a greenhouse with natural light, it’s time to think about the seed-starting soil mix you will use.

Having a light soil mix is essential. You want to avoid a heavy compost mix until the plants are established. Compost is far too rich and can burn the seeds as they sprout. It also can be too heavy, making the growing seed work too hard to push up and through the soil. Start with a light and airy mix. Save the compost-heavy mixes for when potting up tomatoes starts in late spring, and the established plants need to be heavily fed.

Buying commercially made seed starting mix is expensive and typically comes in small bags. If you are only starting a couple of plants, then yes, this will work for you. If an entire greenhouse is packed with seedlings like us, you must make a lot of starter soil.

Pots full of seed starting soil in a greenhouse

Seed starting mix can be straightforward, with as few as two ingredients, or you can blend premade potting mix with more lighteners.

Commercial mixes are often peat moss, pumice or vermiculite, and sand. It’s that simple. And those tiny bags are not worth your time. That’s just limiting your growing potential, no?


“…. is a hydrous phyllosilicate mineral which undergoes significant expansion when heated.”

As I mentioned above, pumice (which is heavy) or vermiculite was the traditional choice of a lightener; however, something even better exists.


“… an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently.” Perlite is very light. And unlike vermiculite, it is more extensive and far brighter, so it is visible that it is mixed in well.

Seed starting soil

A tip? If you need to make a lot of soil up, the stock tanks sold at farm stores work well. Yes, it is a LOT of soil (this stock tank is big enough I could use it as a bath tub). But you’ll use it up if you are growing a lot. They are also very heavy-duty and handle winter well, year after year. I can fit a 2 cubic foot bag of perlite, a 2.2 cubic foot bag of coconut coir, and a 2 cubic foot bag of dry potting soil. Our youngest son happily mixes it up for me; then, I transfer what I need into a small potting tray (such as a concrete mixing tray) to work directly in our greenhouse.

I use perlite and a dry potting soil mix with a bag of coconut coir added for a modern take on it, or I will also do perlite and peat moss or coconut coir as the most simple blend. I find adding the ProMix soil gives a good boost, though. It isn’t heavy. It comes compressed, so it isn’t full of water and stinky. Bonus points always. Overall I keep it at a 1:1 ratio of what I add. So, even if you are making smaller amounts, keep that in mind as you mix it up. You can always bag up your mix, in teash bags, or in a plastic tote, and store it inside for when you need it.

I keep the mix dry until after I have filled pots and seeded. Then I water it, let it soak in, then water it a bit more.

With seed starting mixes, watch the pots to get dry and water gently as needed.

Enjoy is getting ready for spring seeding!