Organic Seed Starting Soil and Soilless Mixes for Gardeners

Organic gardeners can choose from compost blends, worm castings, rock wool, coco coir products, and organic potting soil mixes to start seeds.

If gardeners can start seeds directly in the ground, why isn’t it OK to harvest garden soil for a free indoor seed starting medium? Seedlings that get their start outdoors are missing environmental agents that allow them to thrive in the landscape. The natural fungi present in garden soil that cause damping off in the greenhouse or windowsill are carried away by wind outdoors. Learn about other natural and organic soil mixes and seed starting mediums available for indoor use.


compost sieve

Compost makes an excellent seed starting medium, as the naturally occurring mycorrhizae forms symbiotic relationships with new seedling roots, giving young plants a strong immune system. Homemade compost usually has large chunks that make it unwieldy in small seed starting cell packs, so gardeners may want to use a screen to create a fine seed starting medium.

Worm Castings

Worm Castings

When worms digest decaying leaves and organic matter, they produce a soil product rich in trace nutrients ideal for seed starting. In spite of the resemblance to manure, worm castings are free of odor and won’t burn young seedlings. Using worm castings alone is an expensive alternative for gardeners who don’t practice vermiculture, but worm castings make a good soil conditioner and amendment for seed starting mixes.

Rock Wool

lettuce rockwool

Rock wool, or Rockwool is an uncommonly used but effective soil free medium to start seeds indoors. The product resembles inedible cotton candy, and it’s made in a similar fashion, by spinning molten rock and sand together to form fine fibers. The result is a fluffy growing medium that retains large amounts of water and permits excellent air circulation.

Gardeners can buy rockwool in starter blocks, plugs, sheets, or slabs. Rockwool works well in hydroponic gardening, and gardeners can also mix bulk rockwool with other growing mediums for a customized seed starting mix.

Coco Coir

Basil in coco coir

Gardeners are increasingly turning to the fibers stripped from organically grown coconuts as an alternative to peat moss, which is similar in texture. Peat bogs are not a renewable resource, and their harvesting isn’t sustainable.

Retailers sell coco coir in compressed bricks, which gardeners can store neatly until ready to use, adding water to loosen the fibers. Gardeners can use loose coco coir from the bag, and coco coir nuggets add drainage to seed starting mixtures.

Organic Potting Soil

tomato plant pot

The availability of organic potting soil for seed starting has expanded with the increase in consumer demand. Soil vendors offer certified organic soils blended with guano, compost, worm castings, fish and bone meal, and other additives that make fertilizing unnecessary until seedlings are transplanted into the garden. If gardeners have leftover organic potting soil for containers they wish to use for seed starting, they can add some perlite or shredded coco coir to increase drainage.


About the Author

With the endless passion for organic living, I - Ann Sanders has come up with the idea of creating A Green Hand. Being the founder and editor of A Green Hand, my goal is to provide everyone with a wide range of tips about healthy lifestyle with multiform categories including gardening, health & beauty, food recipe,...