The basics of seed starting indoors - Gardening with Brendan

I gave up on quite a few plants last year when they didn’t germinate, not realising they needed special treatment to get them going. Different seeds, like the plants they birth, can require very different environments to get them going.

Some like it hot. While most plants will germinate fine at room temperature, some seeds need to be very warm and cosy before they’ll come out of their shells. Plants like tomatoes, bell peppers, petunias, rudbekias, calendula and generally those which originate in warmer regions of southern Europe, Asia, African or South America, all seem to prefer it at or above 20 degrees Celsius. If growing these, you may want to make use of your airing cupboard / hot press or invest a few pounds in a heat mat, which can be picked up for as little as £12, and which help keep trays or pots of soil warm to aid germination. In general, germination needs a higher temperature than growing on for almost all plants. So if you are keeping them somewhere warm, once they pop up above the soil, remove them to a slightly cooler place.

Complicating this is the fact that some seeds, even some heat lovers, need light to germinate, while some need darkness, and others aren’t really that fussy. Plants like cornflower, tomatoes, sweet pea, cucumbers, alyssum, pumpkins, marigold, broccoli etc will germinate either way.

Some plants which require darkness, or prefer it are delphiniums, calendula, phlox, violas and pansies.

Plants which need light to germinate include lettuce, coleus, poppies, foxglove, begonia, petunias and yarrow (achillea) and black eyed susan (rudbekia). Many of the seeds which require light are tiny and therefore should be surface sown and not covered. In general, other seeds which should be covered should not be planted too deep to avoid them struggling to get to the surface.

Some seeds can of course be thrown directly onto the soil and watered in to ensure good contact, and a few actually prefer being direct sown. Poppies, love-in-a-mist (nigella) and delphiniums, which all thrive in colder weather, struggle in warmer climes and don’t tend to transplant as well, although the delphiniums would need to be buried slightly for darkness. The problem with this is though that you won’t get anywhere near the same rate of germination and a lot of the young tender plants will be gobbled up outdoors by snails and slugs.

In terms of growing medium, a dark, crumbly multi-purpose compost with a fine enough grain is ideal.

Seed starting compost is very good for germination but virtually useless after it as it contains only enough nutrients to allow for germination.

I’ve found nearly every seed I’ve grown will do just fine with multi-purpose. Just avoid the lumpy, mossy, twiggy varieties and you can usually feel through the bag what type of compost is being sold.

Apart from that all you need are some seed trays, which can be purpose bought or washed out plastic food containers, labels, which are vital for keeping checks of what you’ve sown where, and a bigger tray to water from the bottom so as not to displace the seeds.

For small seeds, try not to over-sow and a small shallow container is fine, but for bigger seeds go for something deep like a plastic fruit punnet so the roots get a chance to develop before transplanting.

Once seedlings emerge, they will all crave day light so a good south facing window sill is ideal for growing on until they are ready to be potted up or moved outside.