In the ‘olden days’ (I refer to the 1940s and ’50s) normal sized seeds were always sown in a standard seed tray made of wooden slats tacked together in such a way that moisture could drain from the base after the seedlings had been watered. They measured 14”x 8”x 2”. Those pieces used for the base were 14” long and a fraction less than 4” wide. As I’ve just implied a small space was left between them for drainage, but not so wide as to allow the seed compost to run out or wash out. In those days gardeners used to place a thin layer of rotted leaf mould over the entire base before filling the tray with seed compost. The leaf mould acted as a kind of reservoir, as well as preventing the seed compost from running out. One of the major disadvantages of the leaf mould was that young seedlings loved it so much they used to root into it as quickly as they could. This was a disadvantage because the roots of young seedlings were very often damaged when they were teased out of the compost at ‘pricking out’ time into a tray or a pot. Nowadays non-rotting seed trays made from plastic have replaced the old style trays. They hardly ever wear out either. Drainage holes hardly ever let compost out, and there is no need at all for a layer of leaf mould to keep it in. Furthermore the type of compost used for sowing seeds is largely peat based and so the problem now is not water draining out from the base, but very often not enough water draining out.
When preparing seed trays for sowing you should try and fill them to within a quarter of an inch of the top. I always fill them right up to the top, strike off any surplus so that the compost is level with the top, and then press my fingers round the edges and into the corners and then level the surface. This generally leaves about the right distance from the top of the tray. I always have a pressing board handy to press over the entire surface, and then it’s ready for sowing. What happens next depends very much on the size of seed which is to be sown. It is very important that the surface is flat and that the seed is sown evenly and thinly. Most seed is normally covered with a very fine layer of seed compost. Very fine seed is not covered at all. When covering seed such as lettuce, tomatoes, African marigolds and the like, I always use a sieve with mesh about an eighth of an inch. Certainly not more than quarter-inch mesh.
But before actually sowing the seed one more piece of preparation is required. I have found that a three-inch diameter pot filled with seed compost and sieved over a tray gives a beautifully even surface on which the seed is sown. Having got this it is a simple enough matter to carefully sow the seed evenly over the entire surface. This done, sieve more compost over the seed until it is covered. Naturally the tray has to be watered, but how? Well if you are really skilled with applying water from a watering can, then use one. But if you have any doubt then the very safest way is to stand the tray in a shallow container full of water and let it soak up until the surface of the compost starts showing wetness. All that remains is to cover it with a sheet of glass covered with a piece of newspaper and place it so that you can look at it every day. When you do this you will turn the sheet of glass over and wipe the wet off it, and keep it so until you see the first signs of life beginning to poke through the compost. At that stage you will remove both glass and paper and place the tray in good light, but under no circumstances in direct light. If you do the seedlings will shrivel up and die. More on this next week.