Author Ellen Vande VisseDownload a PDF Copy of This Article
My Favorite Organic Potting Media
Those Available in SouthCentral Alaska Stores
How to Make Your Own
Incorporate: From a small volume of soil, robust and resilient plants need a complete profile of nutrients and micronutrients, porosity for root development and water retention, adequate drainage and pH buffering capacity. Additionally, the potting soil those plants will utilize should be free of weed seed, provide microbial species richness (a fascinating topic with a growing volume of scientific information) and the opportunity for that species richness to turn into beneficial species abundance.
Organic growers get rapturous about living soil. Sterile potting mixes lack the necessary and beneficial soil biology to feed your plants, hold water, and protect seedlings from a disease called “damping off”. So notice that my favs have a compost component to provide those essential soil microbes.
I love to buy local and support our Alaskan agricultural entrepreneurs. Mr. Al Poindexter of Anchor Point Greenhouse on the Kenai Peninsula makes these two excellent products.
Fishy Peat Mr. Poindexter produces it from kelp he collects on nearby beaches, peat he mines locally, and fish waste from Kodiak processers. He composts this and judiciously tests to insure consistently low salt levels. If you like, add perlite or vermiculite to fluff it up for potting. I use Fishy Peat straight to make soil blocks. It is already the perfect consistency without having to blend some recipe.
Alaska Earth This is Fishy Peat combined with perlite and more peat. Alaska Earth is much more fluffy for seedlings, and has faster drainage, and dries out faster than Fishy Peat. I have seen a generous supply of these at Three Bears in Mat-Su.
ProMix and ProMix HP or BX (It’s not local; probably from Canada.) It is generally sold as compressed bales weighing 60lb. These hefty bags are economical for filling gardening containers as well as growing seedlings, since each bale yields 3.8 cubic yards of potting medium. But moisten it first and wear a mask before you fluff it up. ProMix already contains perlite. The company claims that the HP & BX versions that contain mycorrhizal fungi will enhance plant growth. I buy ProMix, but I consider it dead. It desperately needs compost. So enliven this dead peat by mixing with 1⁄4 sifted compost or worm compost. (Worm compost is the same thing as worm castings and vermi-compost).
Coir or Coco Fiber
Add this block of compressed coco fiber into 2.5 to 3 gallons of water, and PRESTO, you have a potting medium. It holds water well, but is poor in nutrients and soil biology. So, stir in one part sifted compost into 4-5 parts coir before planting. Or use straight coir, but regularly apply worm tea, manure tea, or compost tea to your seedlings in their flats to provide those missing minerals and microbes.
Please see the separate article, The Scoop on Coir for a Potting Medium for more detail and sources in this website. Boreal Coir is sold in Wasilla, AK.
Make Your Own:
The typical purchased organic potting mix has some permutation of the following recipe: 70% peat, 30% compost, lime, and bagged nutrients (i.e. bloodmeal, kelp meal, greensand, rock phosphate, bonemeal, etc.).
Usually vermiculite (a natural mineral that expands with heat) or perlite (volcanic glass, popped like popcorn by fire) is added to lighten the mix and increase drainage.
Sometimes coconut coir (fibrous coconut shells) is included or occasionally other materials (rice hulls, other organic fertilizers). Everyone has their proprietary proportions and tweaks on this recipe.
Making your own mix on site is attractive because the components are simple, compost is usually available locally, and shipping potting mix is very expensive. However, we’ve seen several problems with home-made mixes that have limited plant growth. High salt levels are a common problem, especially when using manure-based composts. “Salts” in this case means any ion (molecule with a positive or negative charge), including nitrate (NO3), ammonium (NH4), K, Ca, Mg, Na and Cl. Notice that most of those are plant nutrients—only sodium and chloride (table salt) are not. Plants need these nutrients to grow, but too much of them burns root tips, causing poor germination and slower plant growth. We measure salts with an Electrical Conductivity meter (EC meter).
Compost maturity is another problem—it must be well-cured. Another problem is the overall fertility of the mix (too much burns; too little causes deficiencies). Home-made mixes have their risks compared to packaged media that has undergone rigorous testing.
Read more at and thanks to: http://www.greenhouse.cornell.edu/crops/organic- resources/Lessons%20Learned%20Mixes.pdf
Conversion and Volume Equivalents:
27cubic feet in a cubic yard (3’x3’x3’)
Loose bags come in 1 to 4 cubic feet
Compressed bales contain 3.8 cubic feet
Four 2 gallon buckets equal a cubic foot
Find various recipes on line from authorities such as Rodale Institute, Center for AgroEcology at Santa Cruz, Eliot Coleman, and others.
What if… you live remotely? You’re economically challenged?
Costs rise. Shipping becomes questionable. Availability wanes.
Time to get creative. Look around at what you have. Sawdust? Sand by the river edge? Muck from ponds? Roadside disturbance? Peat from the tundra? Start blending. Test your blends. The plants will tell you what works. Keep notes about which formulas perform well. This 30-minute video will show you how: https://www.westernsare.org/Learning-and-Resources/Multimedia/Western-SARE-Videos/Building-Soils-in-Alaska-Communities
Or search on line for Western SARE Building Soils in Alaska Communities.
I always have last year’s potting medium left over. There it is, looking at me, taking up space in the pots I want to use this year. I recommend this recipe that I use:
1 part old potting medium
1 part new potting medium such as Fishy Peat, ProMix, or coir
2/3 part compost or vermi-compost
One scoop of A, one scoop of B, 2/3 scoop of C.
Mix well… which is especially easy if you have a wheel barrel and garden fork.
May you have happy seedlings and vigorous container gardens!