Many bulbs readily multiply by producing offsets without any help from the gardener. But as well as taking advantage of this, it is quite simple to grow more of your favourite bulbs using just a few other techniques, including scaling, bulbils, seed and division.
Bulbs can be easily and effectively propagated using a variety of techniques, but always use disease-free material. Try lilies, snowdrops, daffodils, tulips and alliums.
How to propagate bulbs
This is probably the easiest method, although cultivars may not come true to type:
- Collect fresh seed from the spent flowers once they have dried out. Separate from the chaff
- Sow seed thinly on the surface of seed compost
- Cover the seed with sifted compost and top off with a layer of fine grit
- Place pots in a cold frame or unheated greenhouse over winter and ensure the compost is always kept just moist
- Some seed will germinate straight away, sending up a shoot (these bulbs are referred to as epigeal), but some plants, like lilies, will germinate growing roots first, with leaves only emerging the following spring after a cold spell (these bulbs are referred to as hypogeal)
- 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
Some bulbs naturally propagate themselves by seed. To aid bulbs spreading, allow seed capsules to develop on Crocus, winter aconite (Eranthis), snowdrop and bulbous iris plants, and be careful not to weed out their grass-like young shoots.
Some bulbs naturally produce offsets (baby bulbs) next to the parent bulb. Offsets can be removed when bulbs are lifted for storage. They will be identical in type to the parent bulb, making offsets a suitable method of propagation for cultivars as well as species bulbs:
- Detach the offsets and pot up
- Smaller bulbs may take two to four years to flower from offsets, but larger bulbs (Cardiocrinum giganteum, for example) may take five to seven years
- Larger, hardy offsets can be replanted in the ground immediately. Small or tender offsets benefit from growing on in pots until they have reached a larger size
- To encourage offset production, shallow-plant a stock bulb, or notch the basal plate of the stock bulb to promote offset formation
Bulbils can be found in the leaf axils of some lilies including Lilium bulbiferum, L. leichtlinii and L. sargentiae. When ripe, these detach easily and can be pressed into the surface of a pan of compost. Cover with 13mm (½in) of coarse sand or fine grit.
Keep frost-free over winter and plant out the entire pan as a clump the following autumn.
This is a good method for propagating lilies:
- 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
- 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 labelling
- 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 them on individually, covered with their own depth of compost
- If the scales have gone soft, remove them from the bulblets before potting on. If the scales are still firm, or have roots coming from their base, leave them attached to the bulblets
This method works well for daffodils, Hippeastrum, Allium, Fritillaria, Iris and hyacinths.
- Lift and clean a mature, virus-free bulb while it is leafless and dormant
- Remove any papery outer skin and trim back the roots with a sharp knife
- Remove the growing tip and 'nose' of the bulb
- Hold the bulb with the basal plate uppermost and cut it into 8-16 sections (chips), each of a similar size, depending upon the size of the bulb. Make sure each chip has a portion of basal plate
- Leave the chips to drain on a rack for 12 hours
- Place the chips in a clear plastic bag containing ten parts fine vermiculite to one part water. Blow up the bag with air and then seal and label it
- Keep the bag in a dark place at 20ºC (68ºF) for about 12 weeks, checking occasionally to remove any rotting chips
- During storage, the scales (layers) of each chip will separate out and bulblets should form between the scales, just above the basal plate
- Pot the chips up individually in 8cm (3in) pots of free-drainng loam based compost such as John Innes No.2. Insert the chips with the basal plate downwards and the bulblets covered by about 1cm (½in) of compost. Leave the scales exposed – they will slowly rot away as the bulblets develop
- Grow on the developing bulbs in conditions appropriate to the species
How to divide snowdrops 'in the green'
This is similar to division of offsets, except it is carried out after flowering while the leaves (the green) are intact.
This method is often used for snowdrops (Galanthus) and snowflakes (Leucojum) as they do not re-establish well when planted as dry bulbs. The corms of hardy cyclamen and the rhizomes of wood anemone (Anemone nemorosa) may also fail to establish when planted in a dry state, as may the bulbs of the bluebell, Hyacinthoides non-scripta.
- Lift the bulbs with their leaves on when the soil is moist, using a border or hand fork
- Carefully tease the clumps of bulbs apart by hand, trying to avoid damaging the roots
- Ideally, replant singly, spacing them at least two bulb widths’ apart
- Where large clumps include small seedlings, replant the bulbs in small clusters
- Plant to the same depth as before, indicated by a change in stem colour from green to white
- Water in thoroughly to settle the roots