How to mix your own super potting soil

My secret formula for making good potting soil and saving money.

Good, clean potting soil, it’s cheap, and it really works.

I need to repot some older plants and plant some new ones. I’m going to need a lot of potting soil and potting soil is expensive. I’ve been thinking about it for some time and I’ve figured out how to put together a mix that will do a wonderful job of growing our plants over the coming season. A mix like this is cheaper than buying regular potting soil. I’ll do a cost analysis at the end of the article.

Potting soil is an art form. In 1970 when I got a part time job at a commercial greenhouse, my first job was to mix potting soil. It’s a fun job. I’m still doing it 48 years later. Here’s the secret:

On March 31, I did a bit of shopping. I got some soil conditioner, mushroom compost, peat moss, and lime from Willow Creek Nursery.

peat moss, mushroom compost, soil conditioner, and lime for excellent potting soil

The soil conditioner is a finely ground bark. A two cubic foot bag cost $3.00. I’m sure that there are different brand names and different consistencies everywhere. I wanted something to make up the bulk of the soil mix that wouldn’t pack, was relatively lightweight, and would remain porous. It also had to be cheap. I dumped a bag into my wheelbarrow:

Next I needed something to supply growth organisms and to hold a bit of moisture.

mushroom compost — straight from the mushroom farm. This is good stuff.

Many years ago a man from Tennessee brought me pickup truck loads of wonderful black stuff from a mushroom farm north of Chattanooga. Mushroom growing mix is highly specialized and it can only be used once, so the mushroom farm just threw it away at that time. I got it delivered (I had to help shovel it off the truck) for maybe $40.00. Now it costs right at five dollars for a 40 lb. bag—but it goes a long way. I dumped in about a third of the bag, pouring a layer of it on top of the soil conditioner.

potting soil mixing — add the ingredients in layers, they will mix more evenly that way

Next is peat moss. I bought a one cubic foot bag for $9.95. I could have saved money by buying a larger bag but I was thinking more like a homeowner and hobbyist. I figure that this will be enough for four large mixes. The peat moss will help to hold moisture and nutrients, and it is relatively light-weight. I have now made three layers of materials in the wheelbarrow.

peat moss in the potting soil — the peat moss is tightly packed and should be broken up and added as a layer

Most organic soil materials are a bit on the acid side and we need to rectify this. I use a bit of pelletized lime to change the pH (acidity balance) toward slightly basic (alkaline).

lime for potting mix — pelletized lime acts quickly to balance the potting soil

This is important for most plants, but if you are using the soil for azaleas or camellias, you may wish to leave the lime out. Some evergreens also prefer an acid soil. I am a firm believer in the positive effects of lime in potting soil. I just spread a bit on top:

adding lime to potting soil mix — spread lime over the potting soil prior to mixing

There are a lot of different time release fertilizers. Osmocote is a good one. These fertilizers are made so that they will break down over a period of several months. I like a fertilizer balance with a high middle number (phosphorous) but sometimes it’s hard to find and in that case a balanced plant food (14-14-14 for instance) will do.

add fertilizer to potting mix — sprinkle time release fertilizer over the potting soil mix

The next step is fun. Mix the concoction thoroughly. It is also good to add some water after it is well mixed and turn it over one more time. This mix looks good, it sounds good, but more importantly, it feels good—and it’s cost effective—a good product at a good price.

mix potting soil with a shovel — The dry ingredients are easy to blend with a shovel or by hand. Then add a bit of water

It was a beautiful day. My wife has been working on some tree-form camellias and I was able to pot up several of them without spending a fortune on potting soil.

camellia planted with home made potting mix — These big pots use a lot of potting soil, but the plants grow well in them

Here’s my cost:

Soil conditioner, $3.00, mushroom compost, $5.00, peat moss, $10.00, lime, $4.00. I bought four bags of the soil conditioner and using the other additives will make up four wheelbarrow mixes. The one wheelbarrow load that I made for this article used one bag of conditioner and ¼ bag of the peat and mushroom compost. The bag of lime will do about 20 mixes. So this mix was $3.00 (conditioner )+ $1.25 (mushroom compost)+ $2.50 (peat moss)—add on a bit for lime and fertilizer and you will have about ten dollars for three cubic feet of some really good potting soil—and you know what’s in it. Compare that with two cubic feet of comparable, prepared potting soil, which would cost you about $15. This type of savings really adds up over the long haul.

Have fun gardening, and share this with your friends,

John Schulz

Another article that may be helpful this spring is about an easy way to apply liquid fertilizer on your plants

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