Getting your hands inside in a pail of well-rotted, homemade compost or leaf mold is always a pleasurable experience. Plunging it into a bag of the proprietary, store-bought potting mix is usually a letdown, and that letdown often comes at a high cost.
I confess that I feel great displeasure when I purchase bags of potting mix of any kind, not only because they are so expensive but also because I have no idea what is in them or where it comes from, so I prefer to prepare my own whenever possible.
A potting mix of all trades
Most proprietary mixes include a base of either peat or coir, as well as vermiculite for drainage and/or water retention and, occasionally, decomposed organic materials such as lightly composted bark.
Others of these mixes are filthy, some are difficult to wet or re-wet after drying, and some contain so little fine organic matter that water just drains through them. Furthermore, only a few of them have immaculate environmental credentials.
The optimal potting mix is much more than just a product that physically supports a plant’s roots and keeps it upright.
It should also have a good balance of water retention and drainage, a strong cation exchange capacity (which basically implies that it can hold onto and release nutrients), and be generally stable, both physically and chemically.
The main ingredients of a good potting mix
Garden soil is the natural choice for a potting mix base, but unless you have a large pile of good, friable soil that is weed and disease free, you may have to go elsewhere.
Having said that, modest amounts of garden soil can be obtained from unexpected areas. Molehills or the soil from building or planting holes will work well as a base, but remove as much detritus from the soil as possible.
Loam is the foundation of many homemade potting mixtures. It is created by cutting grass turfs into parts and stacking them upside down until they rot down to a soil-like consistency.
The key to a swift conversion of turfs to soil, like with any composting process, is to keep moisture and heat within the heap while excluding air; the hotter the heap, the faster the process.
Loam is only somewhat nutritious, but its great strengths are its ability to hold nutrients that are added to it, its texture, and its ability to hold water and drain quite effectively.
Leaf mold is wonderful, and it’s very simple to make.
Simply fill solid bin bags to the brim with fallen leaves, knot the top to keep out winter rains, poke holes around the base to allow for some air exchange, and set them in a corner for a year.
The resulting soil conditioner will be rich and earthy, making it ideal for use in your blends. It isn’t particularly nutritious, but it does have a high concentration of microorganisms that aid in the battle against pests and disease, and it keeps moisture well and is readily re-wet if it dries out.
Compost from the kitchen and garden is more nutritious than leaf mold and makes an excellent base for most mixtures. If you use it as a substrate for seeds and seedlings, mix it with equal parts loam or leaf mold, or it will be too rich for the sensitive demands of these little plants.
The nutrient value of compost is directly related to the raw ingredients, and the rate at which it rots is directly related to how small the raw materials are chopped and how you create your heap.
The most common error in composting is placing your heap in a cold, gloomy part of the garden; instead, place it in a sunny area, layer it properly, and water it occasionally, and your heap will thrive.
Composted woodchips and composted bark are among the most environmentally friendly soil conditioners available.
They are typical byproducts of multiple industries, may be obtained locally, and have all of the properties required in a soil conditioner once properly composted.
Composted woodchips and composted bark are fantastic materials, but unless you want to wait a long time, you will need to pile them high! Choose a heap that is at least 5 feet X 5 feet, and moisten it thoroughly as you lay it down. All of the chips should be wet.
When you’ve achieved a height of about 5 feet, drape a tarp over the entire structure, tie it down tightly, and leave it to cook for a year. The resulting soil conditioner will be crumbly and sweet-smelling, making it suitable for use as a base in your mixes and a far superior substitute for peat.
Well-rotted manure is rich and nutritious, and it may be obtained in great quantities. Nevertheless, for container gardening of any kind, it should be composted for at least two years before utilizing it as a garden soil conditioner or mulch.
This guarantees that it has completely degraded and mellowed enough to come into close contact with the roots of containerized plants.
Maintain a heated manure heap to kill as many weed seeds as possible, and flip it sometimes to break it up so that any straw or other bedding rots down quickly.
Worm compost contains many of the same benefits as good quality, well-composted kitchen and garden compost or average quality manure, but with a much nicer, finer texture. You’ll be well on your way to a really fine potting mix if you can make enough worm compost.
The greatest amendments to add drainage into a container mix are sharp sand or fine grit. Sharp sand can be difficult to locate because so many sands are too fine-grained to be useful, but a trip to your local builders’ merchant should provide some possibilities.
The grains must be large enough to be rough and gritty between your fingertips in order to execute the job properly. If you can find a good, cheap source of fine grit or small stones, buy a large bag since it will never go to waste, and it will never sour, unlike biological materials.
Additional recommendations
Maintain a close eye on the pH of your mixtures. A pH meter is affordable and extremely useful for a quick check. Most plants require a pH of around 6.5. However, acid lovers require a pH of around 5.5-6, and calciferous plants like cabbages require a pH closer to 7.5.
Vermiculite is an excellent component of many potting mixes, yet, it is becoming increasingly impossible to overlook the environmental impact of including this substance in our potting mixes.
Vermiculite is a mined mineral that is extracted in large amounts from the ground, frequently in massive opencast mines with all of the associated ramifications.
It is then processed at extremely high (and therefore environmentally costly) temperatures to produce the expanded tiny pellets used in gardening, home construction, and industry. It is then put onto ships and carried enormous distances to us. Why not employ perfectly acceptable alternatives, as there are for peat?
Coir is frequently recommended as a substitute for peat since, unlike peat, it is a renewable resource and a natural byproduct of another activity. On the other hand, it necessitates shipping over long distances to reach us, so the environmental points it wins, on the one hand, are offset by the points it loses on the other.
When utilized in the countries where it is obtained, I believe coir is a wonderful and environmentally friendly addition to potting soils.
Compost recipes
Seeds and cuttings
All of these require excellent drainage; hence the amount of drainage materials is relatively high – one-third of the total volume of the mix.
When the roots begin to grow, and the seedlings or cuttings begin to sprout, they are ready to be moved into the next mix.
Ingredients:
- One part sieved and pasteurized loam or sieved and pasteurized fine garden soil.
- One part leaf mold or composted woodchip or composted bark.
- One part fine grit or sharp sand.
Potting on
This stage requires somewhat more nutrients but not significantly more drainage.
Ingredients:
- One part loam or coarsely sieved garden soil.
- One part leaf mold or composted woodchip or composted bark.
- One part rich kitchen and garden compost
High nutrient potting on
This is suitable for annual flowers and any vegetable seedlings.
Ingredients:
- Two parts rich kitchen and garden compost.
- One part well-rotted manure (at least two years old) or worm compost
For raised beds and large containers
Ingredients:
- Two parts loam or leaf mold or composted woodchips or composted bark.
- One part rich kitchen and garden compost.
- One part well-rotted manure (at least two years old) or worm compost.
Ericaceous mix
Ingredients:
- One part leaf mold.
- One part composted bark and/or pine needles.
- One part rich kitchen and garden compost
For succulents in permanent pots
- One part pasteurized loam or garden soil.
- One part grit.
- One part kitchen and garden compost
To Pasteurize, or Not to Pasteurize
This is a difficult question for others, but it is simple for me. I only pasteurize soil that will be used for sowing seeds or transplanting sensitive plants.
I figure that if I get the mix correct and the growing circumstances are good, the plants will be tough enough to deal with any weed or disease competition from their growing medium.
Pasteurizing tiny amounts of soil is simple: half an hour in an oven set just above 180°F can kill most weed seeds and pathogens. Unfortunately, it will also kill off most beneficial microbes, although this tradeoff is worthwhile during the seed/seedling stage.
Simply dampen the compost, pack it onto a deep oven tray, cover it with foil to hold the steam, and lay it in a cold oven before turning on the oven. Begin timing when the oven reaches 180°F and leave it at that temperature for 30 minutes.
Don’t be tempted to boost the temperature or leave it to ‘cook’ for more than half an hour after it has achieved the desired temperature.
At 212°F, the soil becomes sterile, and sterile soil means that all the healthy fungus, bacteria, and microbes are wiped out, and as we all know, all those good microorganisms have an important job to do, so keep it at 180°F.
Concluding
So, there you have it! You now have all the information to make your own compost for your various garden needs. I’ve been using these recipes for years, and I’m trying to pass my knowledge to other gardeners out there, hoping they will find the same successful gardening recipe, just like it did.
Additional resources:
Smart tips for gardening on dry soil
If you see this plant in your backyard, don’t touch it!