Today, as I write this in the third week of February 2013, it is very cold and lightly snowing outside. However, after mid-February the day length extends beyond the ten hour mark, and sun starts to percolate further into the grow-house and conservatory. As soon as I see the tell-tale signs, bulbs sprouting, catkins and buds on the trees and the delicate white blossom on the Prunus Autumnalis, my thoughts automatically turn towards spring-time.
It is counter-intuitive, but this is the time to start off our most delicate summer crops, rather than the robust ones, which we can plant direct into the soil very soon. Now is the time to plant those things which need the absolute longest growing season in order to crop.
I’m thinking in particular of tomatoes, aubergines and peppers, all of which like a nice snug seed bed, inside, in the light and in the warm. These crops won’t germinate unless you can get the soil temperature above 18°C, but they are happier at 24°C. Aubergines come from India, where they can withstand a day-time temperature up to 50°C! So hot and humid, is what we are after.
Even my conservatory/studio is not heated to those types of temperatures all day and all night. So the only way to bring these seeds on in February is by using artificial heat. You can heat the whole room or greenhouse, but it is much cheaper and more controllable to provide bottom heat direct to the seed tray.
The greenest and muckiest way to do this is by using decomposing farmyard manure. But this is a technique best left to the rural gardener, who has the space for such fun and games. In a greenhouse, on a large bench you could sink heating cables into a sand filled tray, but then all the seeds will have to be subjected to the same level of heat.
I have found that the most flexible technique is a simple heated seed tray. Stewart do an adequate variety, though the lids are a bit flimsy (The handles fall off if you try and lift the lids by handles alone!) I will only be using this contraption to heat seedlings for about a month each spring, so there is no need to go money mad. Once the seeds have germinated they will be a bit more tolerant, so I can remove them to an unheated seed bed, later on. I have two identical trays, one heated and one not heated. This works well. The plastic lids double as cold frames on the roof top veg plot later in the springtime.
Most heated propagators come with inner seed trays, which are fine for most seeds. I also have some root trainers, taller seed pods, which allow some of the more vigorous plants to get a good root going, before I have to transplant it.
I have to keep reminding myself that every little seed I plant in February may need a six inch pot by April, and may still be under cover in May or early June. One 52x42cm propagator will yield about 65 individual plants. Even allowing for casualties, that will require a bench four times as long as the propagator itself needs.
I make my own compost, which I shall mix with sharp horticultural sand and vermiculite, to produce a seed compost. The compost can be sieved before mixing, which makes it easier for small seeds to get through. In addition because the compost is not sterilised, I let it lie fallow for a few days before planting to allow any slugs to show themselves. A few ferrous phosphate tablets will soon despatch them. The heat within the compost heap should have killed off most of the annual seeds. But by not sterilising, I know that I’ve got a soil that is teeming with micro-rhizomes, micro-organisms as well as the odd worm. That to me outweighs the inconvenience of eliminating perennial weeds and the odd critter, by hand later on.
I don’t think that seed sewing needs to be an exact science. In the wild seeds simple drop from the plant, they nestle into the ground, probably covered by leaf-mould and then, hey presto! Once spring comes, they push right up. But most gardeners, including me do go through a bit of a ritual when sewing. Once the soil is placed in the seed tray, or seed pods, pick the whole tray up and drop it from about six inches, back onto the bench. This compacts the soil just enough to allow the water to percolate upwards. Press the top gently but firmly with the back of your hand, or a flat piece of wood. You can make finger holes for larger seeds, using the joints as handy measures. Simply drop fine seeds onto the surface. Always sew thinly. Station sewing is best, i.e. sew exactly. Two seeds per station should give a good level of germination. Cover the seeds with seed compost, vermiculite or perlite and label. As a good rule of thumb, seeds should be planted to a depth equal to their size. If you bury them too deep, they may not get to the surface at all. Remember seeds use their own store of food before they break surface, they can’t use photosynthesis. Small seeds have a small food store and will expire before they reach the light, if they are too deep. If you sew seeds too shallow they are likely to fall over when they reach the surface. But this can be rectified to some extent by re-potting.
Some seeds, like tomatoes and peppers like darkness to germinate, so cover with a few sheets of newspaper, or a sheet of card. Keep a close watch every day. Once they have come through the surface the card should be taken away.
Water the compost not the seeds. I place my seeds trays on top of a capillary mat, which delivers moisture to the underside of the pots all the time. It is difficult for the seeds to become waterlogged or desiccated. The warmth and moisture will help to crack the seeds outer casing and get the whole thing going. Water is also used by the seed as it grows towards the surface. Seeds cannot withstand drought at this stage. Once the seedling is present, it is still very delicate, so continue watering from below. If the compost gets very dry, I dunk the tray into a larger tray of water, which will re-invigorate the compost.
Pricking out and potting on
If you station sew, you can afford to let the plant grow for longer in its seed bed, perhaps giving it a push after three or four weeks by applying a weak dose of fertiliser, or compost tea. Once the seeds start to show from the bottom of the pot, it is time to move them on. Pot them on into yoghurt pots, small plastic trays or individual pots. The compost mix can be a bit richer this time around, depending on how long you plan to leave them in-situ.
Potting and re-potting several times, before the seeds get to their final outdoor or greenhouse bed, encourages strong growth. Every time I re-pot I give the little fellows a fillip of new soil, and new nutrients. I aerate the roots and gentle touching of the leaves is supposed to stimulate growth. I think the idea is that this simulates the wind. By potting on little and often I can keep my growing space to a minimum. I can plant a lot of seedlings in a two inch yoghurt pot, and then prick out later into larger pots or, good weather permitting, straight into a cold frame or a protected area of the garden.
It is space that generally inhibits us from planting too early in the spring. As you plant in a heated propagator, you should also be clearing space elsewhere so that the seedlings, as they develop have somewhere to go on to.
I’ll talk more about potting on and hardening off later in the year.