How to Make Your Own Potting Soil

Learn how to make your own potting soil. Combine a bit of dirt, some well aged compost and a handful of sand for good drainage to form an inexpensive and handy planting medium for your new garden seedlings or old-friend house plants.


| December 2008/January 2009



Heating your compost for an hour at 160 degrees will kill fungus gnats and most weed seeds.

Heating your compost for an hour at 160 degrees will kill fungus gnats and most weed seeds.


Illustration by Elayne Sears

How to make your own potting soil. Nutritious potting soil will give your seedlings and house plants a good place to grow. You can save money by using your own soil and compost to make potting mixes your plants will love.

How to Make Your Own Potting Soil

Packaged potting soils are a terrific convenience, but their cost adds up fast in a busy garden. Last year, I paid $7 per 22-quart bag for my favorite, McEnroe Organic, a fair price but is nevertheless dollars out the door. Making only about half of the potting soil I used saved me around $60. Next year, when my pile of rotting sawdust matures, I hope to be potting soil self-sufficient.

Potting soil self-sufficiency is good for your pocketbook, your plants and the planet, and you actually gain convenience by always having potting soil ready when you need it. If you have soil and compost, you’ve got the basic ingredients for making your own potting soil. In place of peat moss, perlite and vermiculite (the three leading ingredients in bagged potting soil), you can simply combine your best soil with cured compost, leaf mold, rotted sawdust (from untreated wood) or a long list of other organic ingredients. Prepare some small batches, mix it with store-bought stuff to stretch your supply, and gradually make the transition to what potting soil should be — a simple, nurturing medium for growing healthy plants or starting seeds.

Giving Up Exotic Planting Ingredients

At least half of any homemade potting soil is homemade compost, but most commercial potting soils are based on some combination of peat moss, perlite and vermiculite — all of which contribute to land degradation and pollution as they are mined, processed, packaged and shipped.

Peat moss comes from wetland bogs in Canada or Michigan, which is not sustainable and probably a long, long way from where you live (see Do You Recommend Peat Moss to Improve Soil?). Many nurseries that grow woody shrubs and trees have found that composted tree bark or wood chips work beautifully as a peat moss substitute. In Walla Walla, Washington, Organix Inc. has developed a technology that turns the cow manure used in methane production into a peatlike material, sold as RePeat. Coconut husk fibers, coir, will stand in for peat moss any day of the week, but unless you live where it’s produced — in India or Central America — coir is about as exotic as you can get. For most of us, the best peat alternatives are leaf mold (rotted leaves), rotted sawdust or a mixture of both. A 4-by-5-foot pile of chopped leaves will take about two years to decompose into leaf mold. In areas where organic rice or other grain hulls are available, composting them will create a light material for fluffing up potting soil.

Rotted sawdust, leaf mold or the abundance of organic matter in garden waste compost also can compensate for the absence of vermiculite, a mined mineral with as many environmental issues as peat moss. Deposits in Montana and Virginia have been found to contain asbestos, leaving a small area of South Carolina as the lone remaining safe source in North America. Personally, I don’t want to pay money to help deplete a limited supply of billion-year-old minerals.

farmer
6/5/2014 6:56:39 AM

We used Coir based soils from Summer Creek Farm. You can check them out on the web. Their soil germinates way better and you have to water less. It even contains an organic fertilizer.


jeanine
3/4/2014 8:38:19 AM

I've been saving steeped tea and herbs and coffee grounds for a while. Are these materials suitable for compost and do they need to be treated in the same way as leaf mold or rotted sawdust?


izeadot
7/9/2013 3:07:11 PM

This is wonderful information.  I want to have a few nice potted plants and a garden and prefer to do it in ways that are natural, sustainable, and environmentally healthy.  Thank you for sharing what you know.


adam white
4/8/2013 6:44:39 AM

This is exactly the information I was looking for. Thank you for putting it together. Previously I was using 50% purchased organic compost, 50% vermiculite. On my first attempt to make my own, I tried a mix of 1/3 compost, 1/3 dirt, 1/3 sand (all 1/4" screened). I made a simple screen, by making a square from 2 x 4's and using U nails to hammer on 1/4" hardware cloth. The mixture got soaked and when potted, It seems as though I have created clay (This formula is very similar to a mixture for adobe... except with organic materials). I will try the methods you suggest, including pasteurizing the soil.






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