Tips on propagating vegetable seedlings We are nearly at that time again when we sow some tiny seeds in compost and see them magically transform into large tomato plants bearing 15-20 kg of fruit each. The whole thing is incredible really. Imagine if you could buy a few little specks (for a couple of pounds) that could transform themselves into a new T.V. or a gearbox for your car? The whole thing is just brilliant. Whether you are sowing a humble radish or climbing vines of purple peas it is a privilege to be the instigator and caretaker of this fascinating process.The other thing I like abut it is it's not very difficult. There are a couple of things you need to get right but once you are set up the rest pretty much takes care of itself.
I have included an article I wrote last year which you can read by clicking the link including my top 10 tips for growing good seedlings. The article covers germinating seeds on a heat source as at this time of year additional heat is essential to trigger growth.
We grow seedlings using heat cables buried in sand as it is the only method suited to the large scale growing that we do for our vegetable seedling business. You can also use a heated propagator or a heat mat to bring the compost up to germination temperature; there are many options available but the same general principles apply.
The main things you need to watch when growing in late Winter or early Spring is your heat light balance and freezing night time temperatures. In brief you need to reduce the heat or take plants off the heat altogether as soon as possible while making sure they don't freeze. If you have too much heat and not enough light your plants will be spindly and weak like the beetroot seedlings pictured above.
We never have enough room on our heat benches to germinate the number of trays we need at our peak sowing times so we stack them up to 3 trays deep. This process takes a bit of minding as the bottom tray will germinate first (it is warmest) so you need to keep a close eye on them and swap them for the top as soon as the first shoots appear.
If the person minding them over the weekend (me) forgets to check them the new seedlings will be starved of light, grow long and weak and have to be discarded. If you are trying to get more from a propagator at home this is a handy method, just check the bottom tray every day and move it to the top when the first signs of life appear. You don't need them all to have come up either, once you see a third of the seedlings the rest of the seeds will have germinated but have just not yet broken the surface.
The most important thing to remember is we only need the heat to trick the seed into germinating, once growth has been triggered they will continue growing at a lower temperature. You can see one of our heat benches above with a single layer of cabbage plants just starting to come up. To save energy I also cover the benches with a layer of fleece to keep the heat in at night which also speeds up the germination process.
Once the seedlings come up any outdoor crops are removed from the heat. We place the trays on wooden pallets on the floor of the polytunnel to keep them off the cold ground before covering with horticultural fleece which protects them temperatures down to -2 or -3 degrees.
Warm climate crops like tomatoes and peppers will need to be kept on a low heat until late March at least depending on the weather. Anyway, you can read our top 10 propagation tips at the link below, I hope you find them helpful. I have also included a link to our Propagation dept where you will find everything you need for early season growing.