Fertilising guide
How to fertilise Showy Autumn Crocus (Colchicum speciosum)— schedule & NPK
Also called Showy autumn crocus, Giant meadow saffron, Showy colchicum.
More about showy autumn crocus
About Showy Autumn Crocus
Colchicum speciosum · also called Showy autumn crocus, Giant meadow saffron · flowering
Showy autumn crocus is a large-flowered cormous perennial native to subalpine meadows of northern Turkey, the Caucasus, and northern Iran, producing impressively large, goblet-shaped flowers up to 12 cm across in shades of rosy-purple to white from August to October. It is the parent of many popular garden colchicum cultivars and is considered one of the finest and most showy of all autumn-flowering bulbs. Plant the large corms during summer dormancy in well-drained soil where the tall flowers will not be obscured by neighbouring plants. All parts of this plant contain colchicine and are extremely toxic to pets and humans.
Growth habit: Clump-forming cormous perennial with a dramatic naked-flower, spring-leaf cycle; very large, glossy ribbed leaves appear in late winter and last until early summer, followed by leafless flowers in late summer to autumn.
Watch for — Flower stem collapse (lodging): The tall, naked flower stems can flop in windy or exposed sites; plant in a sheltered position or adjacent to low groundcover plants that support the stems without obscuring the large blooms. Avoid high-nitrogen soils which produce soft, weak stems.
What fertiliser showy autumn crocus actually wants — and why
Showy Autumn Crocus feeds for next year, not this one — the critical window is after flowering, while the leaves are still green and recharging the bulb.
A low-nitrogen, potassium- and phosphorus-leaning bulb fertiliser (something like 5-10-10) or bonemeal at planting. High nitrogen grows floppy leaves and rots stored bulbs.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for showy autumn crocus: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed showy autumn crocus, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For showy autumn crocus:
Top-dress with a slow-release balanced fertiliser or bonemeal when the large spring leaves appear; the leaves are the sole means by which the corm stores energy for autumn flowering. The rhythm: a bulb feed at planting, a light feed as leaves emerge, and — most important — a potassium feed straight after flowering while the foliage is still green and feeding the bulb. Never cut the leaves off early.
The dormant-season rule matters more than the exact interval: skip feeding entirely when showy autumn crocus is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for showy autumn crocus
Use the bulb-feed label rate for showy autumn crocus; the timing (post-bloom, leaves still green) does far more for next year's display than the concentration.
Feeding always goes onto already-damp soil, never dry roots — water showy autumn crocus first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the showy autumn crocus watering schedule.
Signs you are over-feeding showy autumn crocus
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for showy autumn crocus:
- Tall, floppy, soft leaves that flop over (too much nitrogen).
- Soft or rotting bulbs lifted at the end of the season.
- Lush foliage but few or poor flowers.
Signs you are under-feeding showy autumn crocus
- Progressively fewer or smaller flowers year on year ("going blind").
- Small, weak bulbs and thin foliage.
- Bulbs that fail to come back at all after a few seasons.
If the symptoms point at watering, light or roots rather than nutrition, the full showy autumn crocus care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Bulbs are not container-flushed like houseplants; the equivalent is not over-feeding and lifting/dividing congested clumps of showy autumn crocus every few years so they are not competing for nutrients.
Organic vs synthetic feeds for showy autumn crocus
Organic options
Bonemeal worked in at planting plus a mulch of garden compost or well-rotted leaf-mould is the traditional, reliable approach for showy autumn crocus. UK: blood, fish & bone or Westland Bulb Food; US: Espoma Bulb-tone or bonemeal.
Synthetic / liquid feeds
A proprietary bulb fertiliser at planting and a high-potash liquid (tomato feed) after flowering — UK: Westland Bulb Food then Tomorite; US: Miracle-Gro Shake 'n Feed Bulb or a bloom booster post-flower.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising showy autumn crocus — frequently asked questions
What fertiliser does showy autumn crocus need?
A low-nitrogen, potassium- and phosphorus-leaning bulb fertiliser (something like 5-10-10) or bonemeal at planting. High nitrogen grows floppy leaves and rots stored bulbs. Showy Autumn Crocus feeds for next year, not this one — the critical window is after flowering, while the leaves are still green and recharging the bulb.
How often should I feed showy autumn crocus?
Top-dress with a slow-release balanced fertiliser or bonemeal when the large spring leaves appear; the leaves are the sole means by which the corm stores energy for autumn flowering. Top-dress with a slow-release balanced fertiliser or bonemeal when the large spring leaves appear; the leaves are the sole means by which the corm stores energy for autumn flowering. The rhythm: a bulb feed at planting, a light feed as leaves emerge, and — most important — a potassium feed straight after flowering while the foliage is still green and feeding the bulb. Never cut the leaves off early.
What strength of feed for showy autumn crocus?
Use the bulb-feed label rate for showy autumn crocus; the timing (post-bloom, leaves still green) does far more for next year's display than the concentration.
What does over-feeding showy autumn crocus look like?
Tall, floppy, soft leaves that flop over (too much nitrogen). Soft or rotting bulbs lifted at the end of the season. Lush foliage but few or poor flowers. Cutting or tying off the leaves of showy autumn crocus as soon as the flowers fade is the great bulb mistake — the bulb recharges through those leaves for weeks afterward, and removing them early means a weak or blind display next year.
Should I flush the soil of showy autumn crocus?
Bulbs are not container-flushed like houseplants; the equivalent is not over-feeding and lifting/dividing congested clumps of showy autumn crocus every few years so they are not competing for nutrients.
Keep reading
- Showy Autumn Crocus care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water showy autumn crocus — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise sarracenia oreophila
- How to fertilise sarracenia × catesbaei
- How to fertilise sarracenia × excellens
- All 10153 fertilising guides in the Growli library