Make the Best Seed Starting Mix for Dirt Cheap (It’s Organic Too)

Did you know you can make your own seed starting mix with just three ingredients? And not only is it fast and simple to make, it can save you a lot of money over premade mixes.

You see… When it comes to gardening, I’m all for getting started on a shoestring. I look for good deals on seeds, make newspaper pots for seed starting, recycle household containers for seedlings, reuse egg shells and egg cartons to start seeds, and scour the dollar store for cheap seed starting supplies.

But where I feel I get the most value, especially if I’m starting thousands of seeds (which isn’t hard to do in a season when you think about it), is making my own seed starting mix.

First, they’re relatively expensive. Sure, the price tag on a typical 8-quart bag doesn’t seem too bad, but then you bring it home and realize that 8 quarts isn’t really going to cut it when you have a whole flat of seeds to sow.

Second, some seed starting mixes contain chemical agents to hydrate the soil or supplements to supercharge your plants, which—for starting seeds—are completely unnecessary.

This is because all the nutrients that a seedling needs in its initial stage of life (before it develops its first true set of leaves) is contained in the seed. Think of it like an egg yolk for a baby chick.

A seed does not need fertilizer, compost, or beneficial microbes to germinate, nor does a seedling need any of that to grow healthy and strong in the first couple weeks after germination. (You can read more about seed to seedling anatomy here—it’s truly amazing how self-contained seeds are.)

The benefits of making your own seed starting mix are no premium ingredients to overpay for, no synthetic fertilizers or synthetic wetting agents to worry about, just simple organic ingredients to get your seeds off to a great start.

This blend is made specifically for seed starting and sometimes marketed commercially as a germination mix. It’s very lightweight and fine-grained to help promote baby root growth and ensure the mix doesn’t get compacted in seed starting cells or containers (which are usually only 1 to 3 inches in size).

Used together, these three ingredients provide the perfect level of fluffiness, drainage, and moisture retention for starting seeds.

Sphagnum peat moss (not to be confused with the coarser and more fibrous sphagnum moss that’s typically used to line floral baskets) is an excellent, sterile, moisture-retaining medium. The finer the fiber, the more water-holding capacity it has.

An alternative to peat moss is coco coir. This material is similar to peat in terms of look, feel, and moisture retention, but is made from the fiber of coconut shells.

Perlite is an ultra lightweight volcanic glass resembling white popcorn ceiling, and it provides drainage and aeration. (I wrote more about perlite’s benefits here.)

Vermiculite is a natural micaceous mineral, brownish and granular in appearance, with water-absorbing properties that facilitate re-wetting of the soilless mix. (This guide explains the differences between perlite and vermiculite in more detail.)

All these ingredients are easy to find at most garden centers, but I’ve also linked my favorite sources below if you can’t find them at your local nursery.

Disclosure: If you shop from my article or make a purchase through one of my links, I may receive commissions on some of the products I recommend.

Combine all the ingredients in a clean tub or bucket, and saturate the mix with water. Stir the mixture with your hands or a trowel until it’s thoroughly moistened but not soggy. (The texture should feel like a wrung-out sponge,)

Add as much water as the mixture will absorb. You might be surprised to see how much it holds—peat moss can absorb 16 to 26 times its weight in water.

This initial watering makes it easier to keep the mix uniformly moist throughout the seed starting period, as peat moss can be difficult to re-wet if it’s been left to dry out.

Fill your seedling pots with the homemade seed starting mix, add seeds, and sprinkle a thin layer of vermiculite on top if the seeds need darkness to germinate.

You can save leftover seed starting mix for next season, or use it as the basis of your potting mix.

But… Adding lime is unnecessary in this case.

Although it’s true that sphagnum peat moss is acidic (with a pH around 3.0 to 5.0), natural variations in the bogs where it’s harvested, how it’s harvested, and how it’s processed mean the actual pH level of your store-bought peat may only be slightly acidic.

I’ve purchased many brands of Canadian sphagnum peat moss over the years and have found, from my unscientific home testing with a pH meter, that their pH levels ranged from 5.0 to 7.0.

More than a dozen bags of peat moss from garden centers and online vendors tested slightly acidic to neutral. (Obviously that’s a very small sample size, but I’m confident about my peat-based seed starting mixes since I’ve never had trouble germinating seeds.)

Perlite and vermiculite, the other two ingredients, are considered neutral to slightly alkaline.

If you combine peat with perlite and vermiculite in equal parts, just how acidic does the seed starting mix actually become? (You can always test this to find out.)

If you’re having trouble with this seed starter, there might be other issues at play: the quality of the peat, any fertilizers you might be using, moisture or humidity levels, even your water source can affect germination or seedling growth.

You can also use coco coir instead of peat, as long as you source a high-quality coco coir that’s low in salt.

Some people might feel a little hesitant about the initial investment (2 cubic feet of vermiculite = $20, 2 cubic feet of perlite = $17, 3 cubic feet of peat moss = $12), but a little goes a long way.

If you keep these ingredients dry, they’ll never go bad and you’ll have plenty for your seed starting and potting needs.

Here’s the thing: Garden soil has the advantage of being in the ground and living in harmony with the soil food web. It’s ideally well-draining and somewhat forgiving, as you let Mother Nature take over and aren’t as obsessed over what does or doesn’t take off.

Unfortunately, garden soil tends to be too dense for seed starting and potting. It’s full of weed seeds. It’s teeming with microbes (both good and bad) and because they’re now constrained in an indoor environment in a limited volume of soil, without natural checks and balances, they can wreak havoc on your seedlings in the form of damping off or fungal diseases.

If you’re going to put forth the effort to start your seeds indoors, nurture them, and harden them off until it’s time to transplant, a good seed starting mix will give you greater success rates so you don’t waste seeds (or time).

This post updated from an article that originally appeared on March 15, 2011.