Bob explains why it pays to be picky with what you buy to get the best results
Have you found in previous years that seedlings did not come up, or that your potted-on plants were not performing as you expected? There are many possible reasons: too hot, cold, dark, bright, dry, wet… But unfortunately it might also be that the sowing or potting compost simply wasn’t very good.
When I first started gardening there were only loam/turf/soil-based composts available. Then peat-based multi-purpose ones were introduced, and started being used widely in the 1960s, and more recently peat-free in many formats. From the start I preferred to use my own instead of buying in. However, I regularly ran trials just to compare mine with the most widely available brands. The results were often alarming, with some commercial composts proving almost useless.
There has been improvement recently, with most potting composts now performing at least acceptably. However, sowing composts may still be haphazard, and we really do need to know we have one that’s up to the job. So I suggest you make a similar trial to mine, if you can, to ensure you get more success.
Put composts to the test
It’s simple enough to do, buy bags of as many different seed composts as you can afford. Sow a multi-celled tray with a row of each (remember to sieve beforehand to re-introduce air) and see how your fast-germinating seeds do. Brassicas, radish, lettuce and cucumber should start to come up within a week or less, tomatoes a tad longer, and you can soon have absolute proof whether those sowing composts are worth using for the rest of your precious sowings now and in years to come. Any duds can be used up, or rather risked, as potting composts for already robustly growing plants, or better still used as mulch.
Why is good quality seed compost so important?
Good sowing compost is essential because tiny seeds are easily overwhelmed by poor conditions, and this includes compost that is too rich, because they need little fertility, just air and moisture. However, because of this a good sowing compost is soon not rich enough for growing seedlings, so we move them on to a potting compost which helps them further grow and prosper.
Fortunately most seedlings are robust enough to cope with some variability in the potting composts on offer, but it may be worth repeating a similar trial of several, especially with favourite plants. So pot a few from early batches of seedlings into samples of each brand and see how these do before potting all the rest. It can be a real eye-opener I tell you.
Feed a little and often
One thing you may notice is how dark the leaves of some plants in some composts are compared with others, and these will be the ones in richer material. Then you notice how remarkably soon they all start to wane unless you keep potting them on into larger pots.
Very few potting composts can sustain hungry plants for long without supplementary feeding (unless you give each plant a huge, uneconomic volume), especially hungry varieties such as tomatoes, sweetcorn and cucurbits. So start adding liquid feed, always very well diluted, to their water as soon as they begin to look less than vibrant. Dilute seaweed solution is a superb tonic that’s well worth giving to almost everything at least every week or so. It’s brilliant stuff, but not a feed on its own.
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