It’s been a good long while since we’ve had to make our own DIY seedling mix. When we realized we could just buy seedling mix in the past, via sterile seedling mix or even using ProMix soil, that was totally worth it to us to save a couple hours of labor. But, since we can’t trust our potting soil mix to our baby seedlings this year, this is exactly what we’re going to do.
We know of a few different seedling mix recipes, but the biggest key to a good mix is to use mostly sterile ingredients. So, no compost or other heavily bioactive ingredients. The reason is that these are very common vectors for errant seeds and especially fungi that can cause us problems in the germination process. While you can use either coco coir or sphagnum peat moss in seedling mixes, we generally prefer coco coir as it’s slightly less bioactive and also better for the environment.
The recipe we’re using here is 2 parts coco coir, 1 part vermiculite and 1 part perlite. The part system ensures you can make as much, or as little, as you like. There are a lot of different seedling mix recipes you can use, so ours is just an example and one we like. We’ve linked our soil building guide in the comments, if you want to know more seedling mix recipes that use different materials and ratios. Consistency wise, we’re aiming for extremely well draining, “fluffy” soil that a seedling can really get it’s roots into. Ideally, it shouldn’t “clump together” when squeezed like a potting soil would.
Now this method works for us as we fully disconnect our germination process from our plant growth process. We germinate in seeding trays, but transplant out to larger containers to actually raise our garden starts. We don’t need a ton of nutrition in the early stages, since we’re really just relying on the seed’s initial energy to get to an transplant size. This is the primary reason why we do grow this way, it allows flexibility that simply germinating directly into final containers doesn’t allow. We field this question a fair bit, and we’re giving you a “real life” demonstration of exactly why we make the choices we do.
And just to be clear, we’re only using this mix in our seedling trays. Just to make sure our seedlings aren’t lost to fungi. We’re still going to use the heck out of our “ProMix knockoff” to bring our plants to full fruition. But, we do intend to raise our seedlings “properly” so they are prepared to handle the tribulations that soil may bring.
Oh, and if you’ve never worked with coco coir before, here’s the deal. It usually comes in highly compressed bricks, typically in 1 and 5 kilogram sizes. You hydrate them with water, which will allow them to break apart. They’ll expand by many magnitudes. We often buy 5 kilogram bales and it’s always a “soil show” how much it coco coir actually makes!
