Young seedlings need careful nurturing if they are to produce strong, healthy plants that perform well.
Check daily for seed germination and seedling emergence. Seeds germinating in a propagator or other warm conditions will need careful weaning to the ambient temperatures; most seedlings produced in warm conditions will need a minimum growing on temperature of 10-13C until well established.
The seedlings need good, even light for strong growth, but don’t expose them to strong, burning sunlight; if necessary, shade them with horticultural fleece. Even, all-round light is important, otherwise the seedlings grow toward the light, grow crookedly and become etiolated (long and drawn) and will never perform well. This is usually only a problem when growing on a windowsill.
Keep the compost just moist at all times, using tepid water, to maintain steady growth, but never let the compost become waterlogged.
Transplanting
Transplant the seedlings once they are large enough to handle to give them more room to develop. When pricking out (transplanting) individually, handle the seedlings carefully as both the stems and the roots are soft and easily damaged. Always handle seedlings carefully by holding them by their seed (first) leaves between thumb and forefinger, rather than the stem; if you damage the stem the plant will never develop properly.
Plants in cell trays can be left without pricking out until their roots fill the compost in each module. Small plugs may need individual potting on into 250 ml pots. Larger plugs may become substantial enough to plant directly into their final growing position.
Seedlings in shallow seed trays need transplanting promptly as the roots have less room to develop.
Most young seedlings can be transplanted 2.5-4cm apart in a seed tray or into a 250ml pot, but slow growers may do much better if moved first to a 100-200 ml pot and transplanted to a larger pot once they have developed a good root system. Don’t transplant into large pots, otherwise the roots ‘drown’ in too much compost.
Always wait until the seedlings have developed a good root system, but don’t leave them until the roots have become entangled with each other, as you will find separating the roots of each plant difficult and you may damage them.
Growing on
Water regularly, as needed, with a watering can fitted with a fine rose.
Good potting composts contains enough feed for about five or six weeks. After this time, plants will need supplementary feeding. Feed pricked-out seedlings and plug plants fortnightly with a balanced liquid fertiliser. Larger plants may need weekly applications and tiny seedlings may only need monthly feeding.
If seedlings become lanky, pinch out their shoot tips to encourage branching. You can prevent excessive legginess by growing plants in good light and avoiding conditions that are too warm.