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Mary Lowther column: Time to dish the dirt

Germinating seeds start out better in sterile soil
Large soil blocker. With a blocker, there is no need for pots to plant seeds. (Mary Lowther photo)

By Mary Lowther

The prudent gardener does whatever she can to increase the growing season and protect her crop from predation. This time of year these goals can be achieved by starting plants indoors, affording them both an earlier harvest and less exposure to seedling munching interlopers before moving the production outdoors. In recent columns we discussed how to set up a seed table, which is the first step. Think of it the way an artist does about setting up an easel.

We’ve also talked about saving our own seed, for better acclimatization, as well as how to find other varieties to expand our inventory. To extend the analogy we will compare that to choosing the subject matter, and this week we will move on to selecting the medium. Having chosen tempera, oil or acrylic the artist will prepare paints; the indoor agriculturalist mixes potting soil, which means it is now time to dish the dirt.

At the risk of mixing our metaphors, we already know this wheel is round and the axle goes in the middle: all we need to decide is what colour it should be. For that decision we have the advice of countless generations of experimental growers.

In his book Tomatoes, Cucumbers and Melons, published in 1959, author A.G. Puttoch was quite taken with “John Innes Seed Compost,” made by mixing two parts sterilized loam (garden soil), one part peat and one part coarse sand. Then to each bushel (35 litres) he added one and a half ounce superphosphate and three-quarters ounce limestone, sterilizing the soil by adding formaldehyde or its equivalent and leaving it for three weeks before using.

Today I use a similar mix, but without the chemicals. Germinating seeds start out better in sterile soil because each seed contains all the nutrients it needs to start growing, and sterilizing the soil kills eggs of insects that could kill seedlings. Instead of using problematic formaldehyde to sterilize the soil, I simply pour boiling water into a bucket of the mix and let it sit until it cools. I use a variation of Steve Solomon’s potting mixture: one part best garden soil, one part sifted compost and one part sifted coir (coconut fibre). Blend, then add to each cubic foot: a quarter cup agricultural lime and a cup of vermiculite or pearlite.

I’ve been using the smallest pots to start seedlings and then popping them into another soil mixture once their first two leaves appear. This second mixture is the same one as the first only I don’t sterilize it plus I add one cup of organic fertilizer to each cubic foot.

I might get a small soil blocker to start the seeds in this year because they can be placed into the larger blocks that I already have, without disturbing the roots. When I water the blocks from underneath, they don’t fall apart too much and capillary action brings water up to the seedlings. The water I use for seedlings has been sitting for at least a day so it’s not too cold, with 28 grams of fish fertilizer added to the water for a bit more nutrient.

I’ve sown several seeds in each pot before, cutting off the extras as they emerge and leaving one or two to grow on, but given the rising cost of seed I’m only going to sow one seed per block this year. One could also use a flat, pricking out each seedling and transferring them into pots as they develop two leaves, re-sterilizing and re-using the potting mix.

This may seem like a lot of work, but it pays off when your fresh, delicious produce hits the dinner table weeks ahead of schedule.

Please contact with questions and suggestions since I need all the help I can get.