- One regular sized brick of coconut coir. This will make approximately 2 gallons (8 quarts) of medium.
- One gallon (4 quarts) of organic compost (NO MANURE)
- One gallon (4 quarts) of vermiculite (not a huge bag – it is common to see smaller 8-quart bags)
- One gallon (4 quarts) of perlite (not a huge bag – it is common to see smaller 8-quart bags)
- Old strainer OR screen
- 5 gallon bucket or large tub or container
YIELDS approximately 4-5 gallons of seed starting mix or potting soil.
Want a great potting soil? Use this same recipe, just don’t screen the compost.
- Coconut Coir: You can get this compacted husk fiber of the coconut in compressed blocks/bricks. Ask at garden centers. Look online. One brick regular sized brick makes about 8 quarts (2 gallons) of medium once soaked in one gallon of water. I have purchased bricks for as little as $2.50 each. Add one brick of coconut coir to the bucket and add one gallon of water. Wait until all the water is absorbed, about 10 minutes. Mix and break up any clumps. Warm water works faster than cold water. The last coir I ordered is shown at the bottom of this article.
- Compost: You need to screen the compost to keep the large particles out to make seed starting soil. (If you’re making potting soil, follow these directions but don’t screen the compost.) Put some compost in an old strainer or on top of a screen and shake the screen over a bucket or gently work the compost back n’ forth with a gloved hand. You need about 1 gallon of screened compost in the bucket. Eyeball it – doesn’t have to be perfect. If you want to sterilize your compost see the notes below. This is not required but helps kill pathogens if your compost is fresh and not aged.
- Vermiculite: Vermiculite is a silica and clay mineral that forms in sheets in nature. Bagged, it resembles mica in appearance and absorbs water, helping to prevent the container soil from drying out. Add approximately 1 gallon of vermiculite to the bucket. Mix.
- Perlite: You’ve seen it in nursery pots, it’s white and pebbly. Perlite is a volcanic mineral that looks like small white rocks. It helps promote drainage. You need this, you really do. Add about 1 gallon of perlite and mix. Add warm water to the bucket to reach an all over moist condition.
Whallah! That’s it. Add to your containers and plant seed. Or use with unscreened compost as potting soil. Learn more about our seed starting process here.
What if I can’t find coconut coir?
Substitute 1 gallon of screened peat and make sure it is moistened with water before adding any other ingredients.
WORM CASTINGS (OPTIONAL): Add 1/2 gallon worm castings to the entire bucket after everything is mixed and mix again. Worm castings add minerals and do not contain harsh fertilizers.Did you know that seedlings do not need fertilizer until the true leaves appear, which are actually the second set of leaves.
FYI, this is the coconut coir I purchased this year. Good deal and wicked soft on kids hands. This stuff is fun to use. Drop a brick in a bucket of water an watch it expand. Very clean, virtually bacteria free. Won’t scrape up your skin once moistened. At school I like to ask the students to guess what the brick is made of. They can’t believe it is the husk or hair of the coconut!