There are many reasons to make your own potting mix for seed starting! Bagged potting mix can be expensive, inconsistent, and contain pathogens, disease or other unwanted components! Using a sterile medium is very important in order to give your seedlings the best chance to grow and thrive! Starting seeds indoors is helpful, and sometimes necessary in order to tackle Colorado’s shorter growing season. Starting seeds four to twelve weeks before the last chance of Spring frost is a great way to get ahead!
The go-to recipe I use is a mix of equal parts Vermiculite, Perlite, and Peat moss.
- Vermiculite is a magnesium iron aluminum silicate very similar to mica. The minerals get heated in an extremely hot furnace which “puffs” them up. The granules aid in aeration, moisture-retention, nutrient-retention, and it is lightweight, sterile, non-toxic, and has a neutral pH. Vermiculite also cannot rot or mold on its own.
- Perlite in nature is a type of volcanic glass. For use in the green industry, it is heated to nearly 1700 degrees Fahrenheit, at which point it “pops” and turns into the little white pieces we find in traditional potting mixes. Its advantages in a mix are aeration and draining. It also retains it’s shape under pressure, has a neutral pH, is non-toxic, and contains pockets of space for air and oxygen flow.
- Peat moss holds water and nutrients in place, and makes these resources available to the roots. It is the “organic” component of the potting mix, yet is sterile and disease-resistant. Peat moss will also retain its shape and won’t compact in the containers.
After mixing your ingredients and filling your planting vessels, I recommend watering before planting seeds, as the mix will be completely dry. Moisture will help hold your seeds into place for future watering. Keep in mind that this mix has zero nutrients or fertilizers, which will not be necessary until seedlings have grown several sets of true leaves. My go-to seedling fertilizer is anything with a N-P-K (Nitrogen, Phosphorus, Potassium or Potash) ratio near 19-26-6.
Remember, it is always important to sterilize and wash all used containers for planting!