Lily bulbs in winter: why cold is not the danger, and wet is

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Lily bulbs are hardier than almost anyone gives them credit for. Left in open ground in a temperate garden, the great majority need nothing at all through the cold months — no lifting, no fleece, no straw.

What kills them is not cold but standing water, which is why the plants that die over winter are almost always the ones in pots.

In open ground: leave them alone

• Do not lift them. Lilies resent disturbance and a bulb left in place flowers better than one dug up and stored
• Cut the stems once they have yellowed, not before. The dying foliage is still feeding the bulb, and cutting green stems costs next season’s flowers
• Remove the cut stems from the garden rather than leaving them on the bed — they carry the fungus responsible for lily disease through to spring
• A mulch is useful for one reason only: it moderates the freeze and thaw cycles that heave bulbs towards the surface. Five to eight centimetres of bark or leaf mould is ample — see what mulch does and does not do
• Mark the position. Lilies emerge late, and a fork through a dormant bulb in early spring is a common and avoidable loss

On heavy clay the calculation changes: it is the wet, not the cold, that is dangerous. Either improve the drainage where they grow or move them to a raised bed.

In pots: the real danger

A potted bulb faces two problems the border spares it — cold on every side, and compost that cannot drain away into surrounding soil.

• Move the pot against a house wall, under an overhang. Sheltered from rain matters far more than sheltered from frost
• Raise it on pot feet or bricks so water leaves freely and the drainage holes cannot silt up
• Group several pots together: the outer ones insulate the inner ones, and the mass of compost buffers the temperature swings
• Keep the compost barely moist. A lily bulb has no tunic and must not dry to dust, but a saturated pot rots it. Check monthly rather than watering on a schedule
• Wrap the pot, not the plant, if you wrap anything: bubble wrap or hessian around the container protects the roots, which is where the vulnerability lies
• Never leave a pot standing in a saucer through the cold months

The full container method is set out in growing lilies in pots.

When lifting is justified

Rarely, but there are three genuine cases:

• Ground that stays waterlogged all winter and cannot be improved. Lift after the foliage dies, store in barely moist compost or vermiculite, somewhere cool and frost-free
• Tender species in a cold garden — the Formosa lily and some trumpet types are less reliable than Asiatics and Orientals
• A congested clump that has stopped flowering well, which is a job of division rather than storage — see how to multiply lilies

Stored bulbs must never dry out completely. Check them once a month and discard any that has gone soft at the base.

What good and bad overwintering look like in spring

• Normal: shoots appear late, often well after tulips and daffodils. Patience is not optimism here — lilies are simply late
• Heaved bulbs: the nose of the bulb visible at the surface after repeated freezing. Replant deeper and mulch
• Soft, brown at the base: rot, from standing water. See basal rot
• Shrivelled and papery: dried out in storage. This is the failure mode specific to lifted bulbs

For the plant itself, see the lily care guide, and note separately that every part of it is toxic to cats.