Spring is on its way, whatever the weather is trying to tell us and I am well into the sowing cycle. Most sowing in the propagator is done in March with a big push around the middle of the month. Hardy annuals are sown outside where they are to grow in April or even May but some half-hardy annuals, that cannot tolerate frost, are sown at any time from late January to April in the propagator. I start some early because they take a long time to reach flowering time so an early start means early flowers and a longer flowering season. But consider where you are going to put the seedlings once they are taken out of the heated propagator. Moving them from warmth to a cold greenhouse will not do them any good. Antirrhinums are sown early because they will tolerate low temperatures but begonias, which are also sown early, will not stand cold.
So here is what I do and what I have been up to. All photos (except the past two) are this year’s crop.
First. I have a propagator in a cold greenhouse ( a part is heated to 5c min) and the propagator is about 3mx1m with heated blankets with thermostats that can be set to various temperatures but which provide (at present) a min of 20c. You need to give your seeds and seedlings warmth and, once germinated, light. Very high temperatures are not a huge advantage and 20-25c is quite warm enough. Be careful of small propagators on windowsills – they can get very hot in sun. I open and close the lids of the propagator frequently according to the weather. If in doubt, er on the cool side. Colder conditions will mean slower germination but may prevent the seedlings getting drawn and spindly or from drying out as they start to grow – which will be fatal.
Start with clean pots and trays and fresh compost. I add perlite to the compost to improve drainage.
I use cell trays with six cells for most sowings. If there are up to 25 seeds per pack each pack gets a cell of its own. If there are more seeds then I sow into more than one cell. This means that if the dreaded damping off appears (see below) I may not lose all the seedlings because there is a barrier between the different batches.
Large seeds are sown by hand but, for easy sowing, I often pour the seeds into my left palm, partly fold my hand to make a crease and work the seeds with the finger of my right hand to sow them evenly over the surface. Sowing direct from the pack usually results in a great rush of seeds and uneven sowing.
Seeds including foxgloves, petunias, begonias, poppies, nicotiana, primulas and impatiens need light to germinate. Other, very fine seeds like lobelia are easily buried too so it is best not to cover them with compost. For these I use perlite which maintains some moisture around the seeds so they are less likely to dry out as they germinate but allow light to reach the seeds.
Once the seeds germinate make sure they get light. I move them to a cooler place too so the seedlings stay stocky and easy to transplant. When moving the seedlings always handle them only by their seed leaves. If you damage or break a seed leaf the seedling will survive but if you hold and crush the stem it will die.
Damping off is a fungal disease that kills seedlings. It spreads through the compost, causing the seedlings to constrict at soil level and they collapse. These antirrhinums went from healthy to dying in 24 hours because I did not open the propagator top last Sunday. One day of laziness and disaster struck! Luckily the seedlings in the other two cells were not affected and I saved them.
Damping off is caused by:
Cold, wet compost
Over-firming the compost
Dirty trays and pots
Early sowing in cold, airless conditions
Many hardy annuals do not like root disturbance and it is better to sow them direct in cell trays rather than transplant them. It sounds fiddly but it is not that much of a chore and it is essential for zinnias. But you do not need to sow until late March or April.