Sow lemon balm from late March to May on the surface of a good seed compost and cover with a sprinkling of compost or vermiculite. Place the seed tray in a propagator at a temperature of 20-25C (68-77F) or seal it inside a polythene bag. Keep the compost slightly dry at all times. Do not exclude light as this aids germination which usually takes up to 21 days.
When seedlings are large enough to handle, transplant and grow them on in cooler conditions until large enough to plant outdoors. When lemon balm plants are well grown and all risk of frost has passed, acclimatise them to outdoor conditions over 7 to 10 days. Transplant outdoors in full sun on any moist, well drained soil at a distance of 30cm (12″) apart. Lemon balm plants will tolerate poor soils. This herb is vigorous, but growing lemon balm in containers will help to restrict its growth.