Mature size & growth rate

How big does Spider Iris (Ferraria crispa) get?

Also called Spider Iris, Starfish Iris, Starfish Lily, Black Flag.

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.

Mature size: 20–40 cm tall, 5–10 cm spread

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.

Indoor size vs how big it gets in the wild

Spider Iris is a naturally small plant — it stays shelf- and desk-sized for its whole life, so it never becomes a space problem. Indoors and in a pot, expect 20–40 cm tall, 5–10 cm spread. A pot, your light levels and a little pruning are what set the final size in a home, far more than the plant's theoretical potential.

It grows mostly by adding leaves, offsets or a slightly wider rosette rather than gaining height — the footprint barely changes year to year.

Growth rate and years to mature

Spider Iris is a moderate grower. Realistically, expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Its feeding profile backs this up: apply a balanced liquid fertiliser monthly during the growing season (autumn through spring); cease feeding entirely during summer dormancy.

Want this turned into the right next pot at the right moment? The pot size calculator and the spider iris repotting guide cover when and how much to size up — pot size is one of the biggest levers on how fast spider iris grows.

How to keep spider iris smaller

Good news — spider iris barely needs managing. If you do want to keep it tidy:

Divide or remove offsets when the pot looks crowded to keep spider iris to a single tidy clump.
Keeping it slightly pot-bound and easing back on feed naturally caps the size.
Pinch or remove the oldest, tiredest leaves so energy goes into a compact, fresh-looking plant.

How to grow spider iris bigger or faster

If you want it to fill the space sooner, push the conditions rather than hoping — for spider iris the accelerators are:

It is already in good light; consistent warmth and a balanced feed in spring and summer are the only levers.
A small step up in pot size every couple of years gives the roots a little more room without triggering a size jump.
Feed lightly through the growing season; this plant simply will not race however hard you push it.

Light is almost always the ceiling. The spider iris light requirements page covers exactly how bright a spot it needs to grow at its potential instead of stalling.

When spider iris outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for spider iris:

Roots circling the bottom or pushing out of the drainage hole — it wants a pot one size up, not a bigger room.
Offsets crowding the surface so the original plant looks squashed.
Honestly, spider iris rarely outgrows a room — outgrowing its pot is the only realistic limit.

If it is the pot rather than the room, it is a repotting job, not a goodbye — see the spider iris repotting guide. If you want more of this plant instead of a bigger one, the spider iris propagation guide turns prunings into new plants.

Spider Iris size — frequently asked questions

How big does spider iris get?

Spider Iris reaches 20–40 cm tall, 5–10 cm spread when grown indoors. It grows mostly by adding leaves, offsets or a slightly wider rosette rather than gaining height — the footprint barely changes year to year.

Is spider iris slow or fast growing?

Spider Iris is a moderate grower. Expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Spider Iris is a naturally small plant — it stays shelf- and desk-sized for its whole life, so it never becomes a space problem.

How long does spider iris take to reach full size?

Roughly three to six years to reach mature indoor size, gaining a steady amount each growing season. Light, pot size and feeding move that timeline more than anything else.

How do I keep spider iris smaller?

Divide or remove offsets when the pot looks crowded to keep spider iris to a single tidy clump. Keeping it slightly pot-bound and easing back on feed naturally caps the size. Pinch or remove the oldest, tiredest leaves so energy goes into a compact, fresh-looking plant.

How can I make spider iris grow bigger or faster?

It is already in good light; consistent warmth and a balanced feed in spring and summer are the only levers. A small step up in pot size every couple of years gives the roots a little more room without triggering a size jump. Feed lightly through the growing season; this plant simply will not race however hard you push it.