Seed Starting Mix: The Scoop

Seeds contain all the nutrients they need to produce their first set of leaves, so most will sprout happily on a damp paper towel. (Easy, yes; efficient? No!) If you’re starting seeds indoors in the springtime, there are better ways to get them off to a good start and stave off diseases from the get-go.

Commercial seed starting mix, fine vermiculite, coarse horticultural vermiculite

You might have already checked out a bag of seed-starting mix and wondered, what gives? Why would I need something special to start seeds? The big advantage of these commercial mixes is that they do not contain soil and are sterile, which prevents a host of maladies from plaguing your tender sprouts. Aptly named “soilless mixes,” they’re typically composed of peat moss, vermiculite, perlite, and some added bells and whistles, such as lime for pH balance and a wetting agent that improves moisture retention. If you are using a mix with peat moss, or peat moss alone, be advised that it absorbs hot water much more easily than cold — useful information, when all your sprouts want is to stay moist!

All of the things that soilless mix does are wonderful, but not essential for a budget seed-starting operation. To start my seedlings, I have actually enjoyed more success using horticultural vermiculite alone. This is mica that has basically been popped like popcorn, a process that yields a light, pebbly mixture that does a wonderful job of capturing precious moisture, and of being cheap and easy to store.

Vermiculite does come from a mined resource (mica), so some might object to using it. It’s true that coco-coir, a growing medium produced from coconut husks, is arguably your most sustainable option. This lovely stuff has yet to really penetrate the American gardening market, however, so unless you’ve planned in advance and ordered it online, you’re probably going to be limited to what’s on the shelves at your local gardening supplies store. In that case, opt for coarse horticultural vermiculite, and rest assured that you won’t need a lot. I can make a small, 8 quart bag last me two or three seed-starting seasons. There’s no need to fill a bunch of 4-inch pots from the get-go; one cup of vermiculite will fill an egg carton or two and will be more than sufficient for your sprouts’ initial needs.

In sum: Learn to love the strange, soilless substance that is vermiculite, and save your bucks for later in the season.

2 Responses to “Seed Starting Mix: The Scoop”

  1. katiedL.

    thanks for this! last year i had some issues with my seed starting. i used only coir and the babies stopped after sprouting their firs sets of true leaves. i figured it was a nutrient problem (as i’ve heard that coir doesn’t have any and i was late in realizing the need for fertilizing). i think this year i’m going to add some vermiculite to the coir and just a little of my worm castings to help get the seedlings going better.
    thanks again!

  2. Kate

    That sounds like a potting mix I’d like to dive into (thinking fondly of the time I hand-mixed the soil in my raised bed). Nicely done!

    Potentially off-putting imagery aside, I’m starting seeds in a “homegrown compost”/perlite mix myself this year, since I’ll be starting more seeds indoors this year and wish to spend less time transplanting/potting-up the sprouts.

    While I have read that non-sterilized mixes (and particularly compost) can harbor a teeming lot of pathogens, I have yet to have an issue with my compost mix. I suppose I might be a little more fanatical when starting tomatoes…oh, tomatoes, you’re so bad to me, but I just can’t quit you…

    By way of signing off: keep up the growing, and please keep us posted!

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