There’s a real demand for information on organic potting soil in container gardening, so I thought I’d pass along a few thoughts from my nursery and garden experience.
Peat Based or Not?
There is concern in Europe and the U.S. about the sustainability of wetlands and peat bogs. Some over-harvesting and lack of management have reduced supplies below a sustainable level and the horticultural industry went exploring options.
I note the Canadian situation is a little different as they have regulations about bog reclamation and are world-leaders in reclamation technology. (plus they have so much of the darn stuff)
One such alternative that works well in some trials is coir.
Coir is the shredded up parts of the coconut after processing. So it’s a naturally occurring substance and (the best part) it’s waste material that used to be thrown away. It makes an excellent base for growing.
But having said that, it’s produced in far-away places in limited quantities (with the attendant shipping costs and environmental costs of that) so it’s not available for commercial production and expensive on the home scale relative to peat.
It usually comes in compressed bricks (that darn shipping again) and you’re going to have to soak it thoroughly to expand it
If you’re going to use a material such as peat or coir that is essentially nutrition-free and is primarily to hold the roots, you really do want to give the plants essential micronutrients and something to grow on. Here’s where we can add compost to the mix.
If your compost is perfectly finished and wonderful stuff, you can add quite a bit more than recommended rates without hurting your plants. But if it’s not quite right (and the only way you’ll know is by having it tested in a lab) then you can do some serious damage to your plants quite quickly.
Stick to levels below 10% on the home scale. You’ll find commercial mixes with higher proportions but these have been tested before mixing.
Hint: try growing tomato seedlings in your homemade soil mix before you put expensive plants into it. Tomatoes tend to be quite sensitive to soil problems and if they’re not growing well (or die) it’s an indication your potting soil isn’t right
Plants require mineral charges to get them growing. They get these naturally from soil but unless you add material such as iron to your soil you’re going to find your plants languishing. Again, in practical terms you can use something like fish emulsion on your organic potting soil to add these minor trace elements.
Here’s where compost and fish emulsion shine in creating an organic potting soil that produces a whomping big and healthy plant right from the get-go through to harvest.
My containers are all started off with a shovel or two of compost in the mix and then I use the fish emulsion on my containers all summer-long to produce huge crops of plants.