Bulbs, And Why Timing Decides Everything

Bulbs are unusual among garden plants because the flower for the coming season is already formed inside them. Everything that goes wrong is a matter of timing and of the previous year.

A bulb is a packaged plant

Inside a dormant bulb are the compressed leaves, the stem and, in most cases, the flower bud, all formed during the previous growing season and held in storage.

This means the first year's display depends almost entirely on the conditions where the bulb was grown commercially, not on the garden it arrives in.

From the second year onward the garden's conditions take over, which is why the difference between a bulb that persists and one that fades appears in year two.

Cold is a requirement, not a hazard

Many spring bulbs need a sustained cold period to break dormancy and produce a full flower stem. Without it they emerge with short stems or fail to flower at all.

This is why planting is timed for autumn, since the bulb needs to be in the ground long enough to receive the winter it depends on.

Bulbs grown in containers indoors are usually pre-chilled to supply that period artificially, which is why they behave differently in later years once the treatment ends.

Depth and drainage govern survival

Planting too shallow exposes bulbs to temperature swings and to being lifted by frost, and it produces weak stems that lean under the weight of the flower.

Too deep delays emergence and can exhaust a small bulb before its shoot reaches the light, so depth relative to the size of the bulb is the useful guide.

Most bulbs rot in ground that stays wet in winter, since they are dormant storage organs sitting in cold soil with no growth to draw the water away.

The leaves are next year's flower

After flowering, the foliage photosynthesises to rebuild the bulb and form the following season's flower bud. Cutting it down early prevents that entirely.

The leaves need to die back naturally, which takes several weeks and looks untidy, and this is the main reason bulbs in lawns are best in areas that can be left uncut.

Tying or folding the foliage reduces the light it receives and has the same effect as cutting it, only more slowly.

Why established clumps stop flowering

Bulbs multiply by producing offsets, and a congested clump eventually contains many small bulbs, none of which is large enough to flower.

Lifting and dividing after the foliage has died back gives each bulb space to build itself back up to flowering size over a season or two.

Increasing shade is the other common cause, since a bulb planted under a young tree can find itself in deep shade a decade later without anything else having changed.