Petunia Raising petunias from seed From The Garden Petunias should be sown in early spring at a temperature of 65-70F/17-21C on the surface of a watered seed or multipurpose compost. Some F1 hybrid petunias require light for germination so the seed should not be covered, although this necessitates particular care to ensure that the surface of the compost does not dry out. Covering seed pots or trays with clingfilm is the simplest way to keep the seed constantly moist. The seed is best sown as thinly as possible so that the seedlings have the space to develop two true leaves before pricking out into trays, packs or small pots. Grow on at 60F/16C until rosettes of foliage have developed, then reduce the temperature to below 50F/10C if possible as this will encourage basal branching; at higher temperature the plants are more likely to become lank. Once basal branching has developed, low temperatures are less crucial. The plants can be grown on in these containers until planting time, as early as possible after the last frosts, but if only a few plants are being raised for use in containers they can be moved on into 31/2in pots, or if space is available, can be pricked out direct into these pots. Plants should be hardened off well before planting. First published in The Garden, June 1997  Petunia A-Z   ©copyright 1997 Graham Rice. All Rights Reserved. All Images Digitally Watermarked.