Are you intending to save money and grow your own bedding plants from seed this year? While many can be sown up to the middle of April and still give a good show, some types are fairly slow to germinate and grow on, and should be sown as soon as possible so they are ready for planting out in late May and early June. Pelargoniums (bedding geraniums), begonias and lobelia are typical examples of these as they need 18 to 20 weeks to grow into well-established young plants.
Even if it’s cold outdoors, as long as you have a warm spot to germinate the seed and a bright windowsill for the seedlings, you can make a start – remember, though, that you will usually end up with a lot of young plants, so make sure you have room to give them enough light until the frosts are over; don’t sow more than you think you can accommodate.
A heated propagator isn’t absolutely necessary for you to raise your own bedding plants from seed, but it certainly helps, especially if you want to use a cool or unheated greenhouse. The best propagators are thermostatically controlled to take the guesswork out of the job. The seed packets will usually tell you what the germination temperature is – remember this is the temperature of the compost, which may be different from that of the air above. If you are in any doubt, treat yourself to a soil thermometer; this will come in handy for all sorts of seed sowing and cutting taking jobs throughout the year, not just now.
You don’t need large seed trays of deep compost to sow your seeds because as soon as the seedlings are large enough to handle, they will be ‘potted on’ into individual, small pots or suitable trays. Small yoghurt pots with drainage holes in the bottom are ideal; wash them well then fill with a good seed and cutting compost (multipurpose composts are often too coarse or contain too much fertiliser for seed sowing, especially when the seeds are very fine, like those of lobelia and begonias). Don’t try to economise by re-using old compost as you can often have a failure with this.
Level the surface of the compost with a clean, flat piece of wood, then soak the pots in a shallow bowl of water to dampen the compost from the base. Follow the instructions on the packet, which will tell you whether to leave the seed on the surface or cover it with a sprinkling of fine compost or vermiculite. For instance, begonias need light to germinate, while pelargoniums require darkness. Keep the compost moist during germination by covering the pots with a thin sheet of clear plastic; alternatively place your pots in seed trays and slip the whole trays inside clear polythene bags. The optimum temperature for germinating these slow-to-mature bedders is 24°C, which is why a thermostatically controlled propagator is a useful asset.
An easier option is to buy ready-germinated seedlings from a nursery, which will take some of the guesswork out of raising your own plants at this stage. Your job will then be to pot these on at a cooler temperature as soon as possible. Make sure you buy healthy seedlings, though – if the pots look like salad cress they have been kept too long without potting on or given insufficient light and should be avoided as the resulting plants will always be thin and sickly.
For potting on, use a really good quality compost and trays already separated into individual cells – you may even have some suitable trays saved from buying ready-to-plant bedding in a previous year. These are ideal and can save you money, but do make sure you wash them thoroughly in a suitable disinfectant, rinse them properly and allow them to dry before filling with compost. This can be dampened by soaking, in the same way as described above. Don’t use cells that are too large as the baby plants may not grow away properly if the roots are swamped by too much compost.
Lift the seedlings out gently – the wide end of a nail file comes in useful. If you need to handle them, always hold them by their leaves and not the stems. Transfer them to their new homes – one plant per cell (you can pot-up a small group of lobelia, however, as these will ultimately make a bushier plant) and firm in gently. Place them in good light, but away from direct sunshine, for a day or two to allow them to settle, then move into full sunlight.
The main benefit of raising your own plants in this way – apart from saving yourself a lot of money -is that you have a huge number of varieties to choose from, rather than the limited names you see in garden centres and DIY shops. You will certainly be the envy of your neighbours with bedding or containers that are very different from the rest.