Gardening is no longer confined to the ground, as many of us have long envisioned. These days, along with the overall movement towards cultivating some of our own food, container gardening — growing fruit and veg in pots and planters — is on the rise. This methodology, of course, has opened the door to gardening on apartment balconies, rooftops, patios, and windowsills. But, like any gardening, the success of a container garden has a lot to do with the medium plants are growing in.
Growing in the earth and growing in pots is quite a different thing, and the soil used with each method is, in turn, also different. In stationery gardens, we work to build the soil into a self-sufficient eco-system, using techniques like mulching, compost, and nitrogen-fixing plants. Plants in containers, however, operate in a partially different fashion, as they aren’t growing as part of a natural system. In essence, we — the cultivators — have to piece together the right ingredients for them: a potting mix.
What Makes for a Good Potting Mix
A lot is required of a good potting mix. Unlike garden soil, which, if cared for properly, is constantly replenished with cycling plant life, a potting mix must be long-wearing on its own. It needs to be loose and airy so that drainage is good, which will prevent the mixture from getting anaerobic and prevent the roots from getting the oxygen necessary for the plant to grow well. At the same time, the soil needs to have qualities of water and nutrient retention, as these things won’t be delivered, via rain and organic matter, the same way they are in nature. The mix needs to be made of fine crumbs, strong enough to support a plant but inviting enough for young roots to take hold. The inclusion of microbes, i.e. soil life, is important as roots/plants and microorganisms have symbiotic relationships that keep both healthy. Lastly, in some climates, potting mixes do well to have properties of insulation, as plants are exposed to extremes of weather.
In other words, it’s quite a puzzle to piece together, and that’s without considering the persnickety needs of each individual type of plant. But, don’t worry it’s doable, and all of the ingredients are there to be combined, for much less cost than buying one of the bagged mixes, which tend to be lacking.
Your List of Ingredients
The trick to make a good but inexpensive potting mix is using things that perform multiple functions.
Coconut Coir, aka Coir Peat
Obviously, we want to make ecologically responsible choices here, and coconut coir is a much sounder choice than peat moss. Both of the components perform the same functions. They have a long shelf-life (take a long time to decompose), are great retainers of water, and help to keep the soil airy rather than compacted, as it would be with things that break down quickly. Coconut coir will also add some insulation to the mix.
Vermiculite, Perlite or Coarse Sand
The name of the game here is aeration, and to boot, these elements, whichever we choose, will add moisture retention as well as helping with drainage, though obviously retaining moisture and drainage seem opposites. Vermiculite and perlite are both basically mineral rocks that have been heated to expand their particles, and both are available at just about any nursery. Vermiculite retains much more water than perlite, so it is not recommended for more aquatically challenged plants like cacti. Coarse sand is the cheapest, less hoorah-ed, option but is the best for weighting down plant pots.
What garden would be complete without some organic compost? Ideally, this compost would come from home, but for beginners, with compost not yet ready to roll, a commercial organic compost will work just fine. (Get that home compost going, though.) Compost brings a lot to the table: It has minerals, moisture, microbes and makes the growing media stronger, able to absorb swings in pH balance. Very importantly, the compost needs to be sieved so that it is particular fine in the mixture, filling in the spaces between coir and vermiculite so that the roots are supported.
Putting It All Together
Now that the core ingredients are gathered, the mix can be made. This begins by soaking the coconut coir in water (about half the volume of water as the coir). Add and mix in the vermiculite, perlite or sand (or mixture thereof) as an equal quantity to the coconut coir. Then, the compost (and worm castings) can be added, and the whole thing mixed once more. For a nutritive boost, some people add a little rock mineral mix, slow-release organic fertilizer, and/or seaweed. Then, it’s time to get some plants growing.
Image source: James Lumb/Flickr