The time it takes for seeds to germinate and produce a visible shoot
above the soil varies greatly, ranging from a day for plants like cress
and radishes, to a year or more for some shrubs and trees. Note that the
first pair of leaves to develop may look different from those that
follow. They are called the “seed leaves.”
If you are germinating seeds in darkness, check them regularly and move
into good light once the seedlings emerge to encourage sturdy and
healthy growth. They will grow tall, thin, and pale if left in the dark,
but keep them out of bright, direct sunlight, which can scorch tender
leaves. Keep seedlings warm, although they usually tolerate lower
temperatures than those for germination.
Do not let the seedlings dry out at any stage, but avoid overwatering,
which can drown the roots. Use a copper fungicide to reduce the risk of
damping-off disease. Water small seedlings from below as for seeds, but
more robust kinds, such as lupines and peonies, can be watered gently
from above. Use a watering can with a very fine spray, and start and
finish with the can to one side of the container to avoid letting heavy
drips fall on the plants. Allow containers to drain thoroughly after
watering, and never keep them permanently in trays or saucers of water.
- Use plug plants if you don’t have time to raise plants from seed. Water them when they arrive, and use the blunt end of a pencil to push the plug plants out of their modules.
- Grow plug plants on in module trays filled with potting mix, making holes in the soil using a dibber or pencil; keep the plants in a light, airy place. Water from below by placing the module in a tray of water.
Getting Ready for the Garden
When you have pricked out your seedlings, grow them on at the
temperature recommended on the seed packet. Check them daily and water
whenever they look dry. Plants in trays can usually remain there until
they are planted out, but some vigorous seedlings in pots may need to be
moved again into containers 1–2 in (3–5 cm) wider than their root
systems. If planting out is delayed and the foliage starts to turn
yellow, fertilize with a balanced liquid fertilizer.
Plants that have been raised indoors make soft growth that is vulnerable
to wind and cold. They must gradually be acclimatized to conditions
outdoors—this is known as “hardening off.” Several weeks before planting
out, place plants in a cool spot indoors. A week or so later, stand
them outside for a few hours each day somewhere that is both sheltered
and shady, covered with a double layer of horticultural fleece. It is
important to bring them in at night. Leave them out for a little longer
each day and then remove one layer of fleece. About a week before you
plant them out, remove the fleece during the day, but leave them out at
night still covered by the fleece.
If you have an unheated cold frame, place the containers of plants in
this instead of using fleece, keeping the lid shut for a few days.
Gradually increase the ventilation, opening the lid just a crack to
start with but eventually leaving it fully open, at first during the day
and then at night too.
Plant out as soon as the young plants are hardened off and the weather
is suitable: mild, damp conditions are best. Wait until all threat of
frost is past before risking half-hardy plants outdoors. Prepare the
site thoroughly in advance, and water the plants well and leave to drain
Tap each side of a tray sharply on the ground to loosen the soil, then slide it out in one block and separate the plants carefully with your fingers or a trowel. Release plants from modules by pushing on the base of the cells; some modules are torn apart. Check the seed packet for planting distances. Make a small hole for each plant, carefully place it in position, draw the soil over the roots, gently firm it down by hand, and water it in.