Thinning Out Bulbs
You may find that mature bulbs begin to flower less freely than in previous years - this is usually due to overcrowding. However, unless the bulbs are visible near the soil surface, as with Guernsey lily (Nerine bowdenii), this may not always be obvious to see.
Thinning Method
- Use a garden fork to lift the whole clump as the leaves die down, taking good care not to damage them. However, when dealing with bulbs that prefer to be lifted in leaf (or 'in the green'), lift them just after they finish flowering.
- Divide the clump of bulbs by hand, separating first into smaller clumps and then into individual bulbs.
- Discard any unhealthy bulb, and remove any dead or diseased material from around the remaining bulbs.
- Clean the good bulbs, removing the loose tunics, so that they are ready for replanting in freshly prepared soil.
- Replant the bulbs as they were originally, in soil or in grass, positioning them in irregular groups. See planting in soil or grass for more details.
Crowded clumps should normally be lifted during the dormant season, before the root growth starts. However, some bulbs respond better when lifted when in leaf (in the green), such as:
* hardy cyclamen
* wood anemone (Anemone nemerosa)
* snowdrop (Galanthus nivalis)
* winter aconite (Eranthis)
* bluebell (Hyacinthoides)
Damaged or Diseased Bulbs
If you have lifted the bulbs and find them to have deteriorated rather than become overcrowded, inspect them carefully for pests and diseases. If there is no obvious reason for their poor results, replant them in a different well drained position with sufficient light and nutrients. Alternatively, grow the bulbs in pots in a greenhouse or cold frame until they recover.