When growing plants in containers, it’s important to use a good potting soil. It must have good water retention but also drain well, so that the roots can breathe and you don’t end up with root rot. And it must have a balance of good plant nutrition so that your plants thrive.
Why Make Your Own Potting Soil?
Making your own seed starting medium will generally save a great deal of money. Fortunately we can get truckloads of potting soil from our municipal compost system for less than $20 (photo here). But if you can’t obtain cheap potting soil this way, or if you need smaller quantities, you can easily make our own.
When you make your own, you also know what is in it. You can make sure you have the correct proportions of ingredients for the individual needs of your plants. And you can save energy and CO2 output by using locally-sourced or homegrown compost.
Why Make It Peat Free?
I have had debates with other gardeners about this – it is certainly a point of contention for many gardeners. Essentially, from what I have read, peat gathering destroys the wetlands and forests where peat moss grows. This is a problem for several reasons. Wetlands, as we all know, are teaming with life and are essential hosts to a great number of plants, mammals, birds, and microbes. Peat is also a carbon sink, meaning that it soaks up carbon, a major greenhouse gas. When peat is harvested, that carbon is released into the atmosphere.
To me, the arguments for using peat sound an awful lot like the arguments people use for cutting down forests in the Pacific Northwest. People say it is renewable if we plant tree farms, or we are only using a small portion of what is annually harvested – construction and large corporations use so much more. And there are many other rationalizations. But as soon as one sees a clearcut forest or a “sustainably planted” tree farm, it becomes clear that these are not good things for a number of reasons: biodiversity and whole ecosystem depletion, loss of important carbon sinks that now contribute to global warming, whole beautiful forests gone forever.
Some gardeners argue that we only use a small portion of the total peat that is depleted each year. Most of it is depleted for cooking fuel (peat is an early form of coal), farmland, or deforestation. Even if this is so, why would we – as gardeners and cultivators of the earth – contribute to this ecosystem depletion in any way, if we don’t have to?
Gardeners argue that peat is renewable. But first off, it is not renewable at the rate we use it. Second, while peat may be regrown and reharvested, just like a tree farm, it has lost its biodiversity. It is no longer a healthy ecosystem, no longer host to the millions of creatures that need it to survive. And third, it is no longer a carbon sink.
Please take a couple of minutes to watch this video:
If we don’t have to deplete a forest – eg, by using recycled or hemp fiber – why should we? If we don’t have to deplete a peat bog – eg, by using coco coir, which is a byproduct waste that is in great surplus – why should we?
The Royal Botanical Gardens has a quick article about peat here, Friends of the Earth has some great articles (and a deeper PDF article), and Wikipedia is a great source for learning more. In my personal belief, the only thing that is better than coco coir is to grow your own peat moss, if you have the space. Since I don’t have the space, I use coco coir. Coconut coir is made from the discarded hulls of coconuts – it’s a byproduct of the coconut industry, which produces large surpluses of it.
Recipe I Use For Making Potting Soil
- 1 Part Aged Compost (locally sourced or homemade)* or 1/2 Aged Compost, 1/2 Aged Manure
- 1 Part Coconut Coir
- 1 Part Pumice (a volcanic rock) or Perlite (a volcanic glass)
- 1 Part Sand
*Aging of compost and manure does two things: it breaks down the nutrients for the plants to then take in, and it cooks out the bad microorganisms and seeds that you don’t want. Without aging manure, the high nitrogen content may burn plants.
- Coco coir (aka coco peat) comes in several forms. You can buy it as a brick or bale that you’ll need to hydrate before using, or you can buy it already hydrated. Most garden supply stores carry one or both versions, or you can find them online. Hydrate the coir bricks and bales by sub merging them in water until they are fully saturated (usually the packages have clear instructions for how much water to use, but always err on the side of less – you can always add more!). They will grow to at least 5 times their size. Then fluff it with your hands, to make sure the fibers are separated from one another.
- Then mix all the ingredients together well. That’s it!
- If you don’t want to use coconut brick, you can try using leaf mold or humus, as laid out in the recipes found here. Many gardeners do this. There are several other recipes you can try there as well.
- Rob‘s Recipe: Mix two parts compost to one part vermiculite or perlite. Fluff up well. Makes the compost lighter for pots.
- If you have a different recipe, please write it in the comments and I will add it here!