I am very impressed with a neighbour who has put notification alerts on the phone to remind her when to sow seeds, and then again when to check their progress and possibly pot-on or start the hardening-off process. However, I am more delighted with our coining of the phrase “germination station” for the heated pads in the small greenhouse which protect the soon-to-be seedlings!
One thing I have learnt is that the only seeds which need to be sown direct are carrots and parsnip as they do not tolerate root disturbance and will respond by growing knobbly and misshapen. Beetroot, radish, swede and turnip can also be somewhat super-sensitive but will tolerate starting off in trays as long as they are planted out within 3 weeks of sowing.
It seems that using seed tray / modules are the way to go as this is a protective environment, whether on a warm windowsill, or in a greenhouse or polytunnel. Good protection allows strong early growth without the plants being battered by wind or rain, as well as being out of the way of rampantly hungry slugs! Module plants also give a longer growing season by approximately four – six weeks when the young plants can be placed in the warmer soil in May.
May?! That’s far too long away away in my mind!
Therefore, trying to get ahead by starting seeds off early means tricking them into behaving as if spring has arrived and this means …. heat. The rule of thumb is 18˚C for cool climate crops and 20-22˚C for warm climate plants. These germination temperatures refer to the soil/compost rather than air temperature – hence the germination-station heat pads!
But by starting off early it is important to avoid raising leggy seedlings and that means therefore balancing the amount of light received in relation to the amount of heat enjoyed. So… the cold-climate vegetable seeds need heat to germinate but as soon as the shoots emerge, they need to be cooled otherwise they will grow like mad looking for the extra light implied by receiving the heat that shocked them into sprouting in the first place (does that make sense?). It is best (apparently) to then put the seedlings on benches or at least off the floor (on pallets, for example) so they are still protected from the cold earth and also to prevent roots growing into the ground. The seedlings should be hardy enough to survive in an unheated greenhouse or polytunnel and will grow in balance with the available light.