Bulbs can be easily and effectively propagated using a variety of techniques, but it is imperative that only disease-free material is used. Remember that many summer-flowering bulbs are tender and will require overwintering in a warm glasshouse or conservatory.
Seed
This is probably the easiest method although cultivars may not come true to type. Having separated out the chaff, the fresh seed should be thinly sown on the surface of John Innes seed compost with added gritty sand in deep pots. Cover lightly with sifted compost and top off with a single layer of grit. Place pots in a cold frame or cool glasshouse over winter and ensure that the compost is kept just moist.
The seedlings can usually be potted up in their second year but they can take a number of years to develop to flowering size; for example tulips may take up to seven years to flower.
Division
Bulb
offsets can be removed when bulbs are lifted in the summer (tulips) or autumn (lilies). These will be identical to the parent bulb, so it is a suitable method for all species and cultivars.
Detach the offsets and dust with a fungicide (such as Vitax Yellow Sulphur) prior to potting up the smaller bulbs which may take two to four years to flower (Cardiocrinum gigantium takes five to seven years). Larger, hardy offsets can be replanted in the ground immediately. Shallow planting stock bulbs or notching the basal plate can promote the formation of offsets.
Bulbils
Bulbils can be found in the leaf axils of lilies such as L. bulbiferum, L. leichtinii and L. sargentiae. When ripe these detach easily and can be pressed into the surface of a pan of compost. Cover with 13mm (0.5in) of course sand or fine grit.
Keep frost free over winter, and plant out the following autumn.
Scales
Lift and clean a mature, virus free lily bulb in late summer or early autumn. Discard any damaged outer scales. Snap off a few scales from the bulb as close as possible to the base and dust thoroughly with a fungicidal powder as above. Place in a plastic bag with a 50:50 mix of slightly damp peat substitute and perlite. Shake the bag and fill with air before sealing and labeling. Place in a warm (21°C/70°F), dark place for six weeks. Some lilies such as Lilium martagon need a further six weeks at 5°C (41°F).
When bulblets appear at the base of the scales, pot on individually, covered with their own depth of compost. Do not remove the scale if it has roots coming from the base.