Getting it to bloom

Why won't my Spider Iris bloom? (and how to make it flower)

Also called Spider Iris, Starfish Iris, Starfish Lily, Black Flag (Ferraria crispa).

More about spider iris

About Spider Iris

Ferraria crispa · also called Spider Iris, Starfish Iris · flowering

Ferraria crispa is a winter-growing South African corm from the Iridaceae family, producing unusual, deeply fringed, star-shaped flowers in shades of brown, purple, and cream with a distinctive spidery appearance and a strong, carrion-like scent that attracts fly pollinators. In the UK it requires frost-free glasshouse or conservatory conditions, as it cannot survive freezing temperatures; outdoors it is only permanent in the mildest frost-free climates. The most critical care point is to keep the corm completely dry during its summer dormancy, as summer moisture will cause rot. Ferraria crispa belongs to the Iridaceae family; iris plants are listed as toxic to cats and dogs on the ASPCA database, and this genus should be treated accordingly.

Plant type: flowering

Watch for — Failure to flower in low light: Plants placed in inadequate light during the winter growing season produce leafy growth but no blooms. A south-facing glasshouse spot or supplemental grow-light in dark winters is needed.

The reasons spider iris isn't blooming

Almost every non-blooming spider iris traces back to one of these, roughly in order of how common they are:

Bulbs were not chilled long or cold enough (a problem in mild winters or with un-chilled forced bulbs).
The winter was too mild or the plant too sheltered to bank enough chill hours.
Foliage was cut down too early last year, so the bulb could not recharge for this year’s bloom.
Too little sun during the growing season to build the reserves the flower needs.
Excess nitrogen feed driving leaf at the expense of flower.

Skipping the cold period (or buying un-chilled bulbs in a mild climate). Without real vernalisation there are no flowers.

The fix — how to get spider iris to flower

Let it get genuinely cold. Leave spider iris outdoors (or in an unheated, cold spot) through winter — do not mulch heavily or shelter it from the cold it needs.
Chill the bulbs properly. Use pre-chilled bulbs, or give 12-16 weeks of cold (around 4-9 °C / 40-48 °F) before planting in mild climates.
Feed the foliage, then leave it. Let leaves grow and feed the plant after flowering; never cut foliage down until it yellows naturally.
Be patient after any move. Expect a settling year (or two to three for peony) with few or no flowers after planting or division — this is normal, not failure.

Light and feeding do most of the heavy lifting here. Dial in the spot with the light guide for spider iris and get the feeding right with the spider iris fertilising schedule — the wrong feed (too much nitrogen) is one of the most common silent reasons a healthy plant makes leaves instead of flowers.

Bloom season and what to expect

Spider Iris flowers in its season (typically spring for chilled bulbs) once the cold requirement is met, then dies back to recharge for next year.

Post-bloom care so it flowers again

Let the foliage die back fully before tidying — it is recharging the bulb. A light feed after flowering supports next year's display.

For everything else this plant needs day to day, see the full spider iris care brief and its watering schedule — a stressed, badly watered plant rarely has the energy to flower at all.

Spider Iris blooming — frequently asked questions

Why won't my spider iris flower?

Spider Iris needs a real cold period (vernalisation) to flower — the winter chill is the signal that ripens the bud inside the bulb or crown. The most common reason it is not happening: Bulbs were not chilled long or cold enough (a problem in mild winters or with un-chilled forced bulbs).

How do I make spider iris bloom?

Leave spider iris outdoors (or in an unheated, cold spot) through winter — do not mulch heavily or shelter it from the cold it needs. Use pre-chilled bulbs, or give 12-16 weeks of cold (around 4-9 °C / 40-48 °F) before planting in mild climates.

When does spider iris normally bloom?