Indoor gardening

When the sun is shining at this time of year, green fingers can get itchy. We want the season to start. In a backwards sort of way, I feel if I start sowing seeds then spring will come. If only it were so.
To sow or not to sow…

There is a balance to be struck when deciding the time to sow seeds, especially while light levels are so low and heat is expensive. It needs to be warm to germinate many plants. If it is too cold then their seeds will germinate more slowly or not at all, and the seedlings will be less lively. If conditions are too warm, they may germinate well and grow vigorously but soon become stretched (also known as ‘etiolated’) because light levels are low.

If your seedlings are weak, they will often recover but not reach their potential. Sometimes they just won’t recover. There is an optimal time to sow each type of seed to get good sturdy plants. You do need to sow some veg early enough because they need a long time to develop in their earliest stages.

Veg like chilies, aubergines and tomatoes, and flower growers will suggest lobelia and others, all need an early start, and at this time of year they must be given warmth. They will not stand even near-frost.

The ideal we aim for is having sturdy plants ready to plant out as soon as conditions are right. But what is ‘right’? Here is the difficulty: in our changeable maritime climate we can have a mild spring with no frost after the middle of March, or we can have a cool windy spring, or a fine spring with a frost at the end of May!

As seedlings grow, they need light, more space, and they will need ‘hardening off’, or acclimatizing. Do you want to spend time outside without a jacket just now? The aim is to let them adjust to their final growing conditions gradually. If they will end up in a warm glasshouse, acclimatizing isn’t an issue.

How can we know when to sow seeds so that our young plants keep growing without being stopped in their tracks by a sudden cold spell (known as a ‘check to growth’)? This is important, if they are checked they can take awhile to recover, which sets them back—better to sow them a week or two later.

It all depends on the hardiness of the species and the conditions we can provide for the young growing plants. Once they have germinated we want them to grow steadily without checks.

I’d like to put out a call to anyone who grows tomatoes well. What is your timing and your techniques for getting good sturdy plants? Tomatoes are from central America and they demand a lot of light and warmth. They are known as ‘tender’ plants, the opposite of ‘hardy’ plants. They dislike cold and won’t tolerate any frost.

Hardy plants will germinate outside (some weeds are already on the go now), but to get an earlier crop or longer succession you can sow some in pots in a windowsill or greenhouse. They can go outside a lot earlier but will still need hardening off and some shelter from wind and cold.

Tender plants need a lot more care. The speed of growth depends on the amount of warmth and light provided. There are many horticultural lamps available for this purpose.

To start these plants off, we use a soil warming mat. This is great for germination when put in a warm room. We also have a few overhead lights which are switched on when the seedlings are up. There is enough room for pots of chilies and aubergines (which benefit from early sowing, end of January/early February) and for them to be then potted up into small pots.

The seedlings will need pricking out, which means transplanting them when little to give them enough room to develop. Don’t put them into too big a pot too quickly. It is best to first move them to a small pot, then a larger one once their roots have filled the first pot. Alternatively, space them out in a seed tray. Keep potting them up as their roots fill their pots to prevent a check to growth.
The next stage is finding somewhere light enough and less warm to slow tender seedlings down but not too much. Windowsills are ok but once curtains are closed the temperatures can drop sharply. Light levels may also still be too low.

It is possible to warm just a section of a glasshouse. For many years we bought a few tomato plants late in spring to grow on in the frost-free section. This also provides space to sow and grow on seedlings of plants that actually prefer it cool to germinate, such as lettuce.

Once plantlets are growing strongly and weather permits, they need to be readied for the great outdoors. Cold frames and cloches are very useful to complete hardening plants. They give minimal frost protection but good wind protection. After the plants have adjusted to the new conditions you can move them out of their shelter during warm days and back inside at night for a week or so.

Advice of an experienced gardener who grows vegetables in your area is invaluable. If you live halfway up a hill, you may have shelter from strong winds or miss the late frosts which affect those living downhill. Your location determines your own micro-climate. A grower who lives nearby can explain what they do and when, and you can then adjust their schedule to your conditions.

Seed packets and many gardening books or websites are often written by growers living much further south, where conditions tend to warm up more quickly. To adjust your sowing dates for your different crops to your conditions, find out when the last frost occurs on average. With experience you will determine how long it takes in your conditions for plantlets to get to a good size and for it to be safe to plant them out.

If you are planting tender plants outside, add another few weeks beyond the frost date so that night temperatures warm up as well. For plantlets of very hardy species, which have been well acclimatized, you can plant these nearer the frost date and keep some fleece available in case frost or strong winds threaten. I prefer not to rush planting out which may mean less early cropping but also less danger of plantlets being badly damaged. But neither should you delay unnecessarily so as not to check their growth.

Most hardening off takes place in May or June, and I must hold off most of my sowings for at least a few more weeks to have my little plants at the right stage and size. But if you can’t wait, sow a few lettuces and a few cabbages in pots—you won’t want too many at once anyway. If they don’t thrive, you can eat the plantlets as micro greens. You can also sow a whole mushroom tub or some pots specifically for this purpose, which will fit on a windowsill. Add a few beet seeds for colour.

Some years you will get it all just right, so take note of when you sow. Other years the weather plays tricks, but we have a few up our gardening sleeves, which I’ll discuss soon. Meantime, robins and great tits are starting to sing and their timing is a sure sign of spring on the way.