How to plant, grow & care for Crocosmia

Summer is the season of bold colour in the garden – hot colours such as reds and oranges can clamour to create a spectacular display and nothing contributes more vibrantly than crocosmia. The rich, warm colours of this lovely group of bulbous perennials (originally from South Africa), comes from fiery flowers on arching spikes and long green foliage.

Even without its hot flowers, cocosmia’s slender green leaves sway pleasingly in a breeze creating movement through the flower beds. The sword-like foliage of any crocosmia helps to break up the monotony of mound-forming perennials, and some form large clumps of excellent foliage for mixed border combinations.

Details Where & when to plant How to plant Care guide Pests, diseases & common issues Frequently-asked-questions

Details

Calendar

Jan J

Feb F

Mar M

Apr A

May M

Jun J

Jul J

Aug A

Sep S

Oct O

Nov N

Dec D

Sowing

Planting

Flowering

Seasonal checklist

Spring

In early spring, plant corms direct in borders and pots.
In late spring, plant young plants in borders and pots.

Summer

Add a good layer of mulch before the autumn frosts.

Autumn

Continue to deadhead and pick your cosmos, which will help them flower reliably until October.

Winter

Plan which varieties of crocosmia you’d like to grow the following spring.

Where & when to plant

Where to plant

Soil type

Light, well-drained and moist soil is best for planting crocosmia corms and plants. On heavy soil, add plenty of grit to the planting position to improve drainage.

Aspect & position

Pick a position in full sun to get the best from your crocosmia, though it will tolerate light shade.

When to plant

Plant crocosmia corms in early spring and young plants in late-spring to early summer.

How to plant

In early spring, plant crocosmia corms about 10-15cm (4-6in) apart and 10cm (4in) deep. They are best planted in light, well-drained soil. On heavy soil, you’ll need to add plenty of grit to the planting holes.

In late-spring to early summer, plant out young crocosmia plants – these are really effective planted in groups of three or more. Choose a position in full sun and plant in moist but well-drained soil. Sprinkle mycorrhizal fungi (Rootgrow) into the base of the planting hole and water well after planting.

Photography by

Jonathan Buckley

Care guide

Watering

Water during periods of drought, and water containers regularly when the plants are starting to flower and when growing at full tilt.

Fertilising

Crocosmia growing in the ground won’t need extra feed, but add fertiliser regularly to plants growing in containers to keep the display looking good.

Deadheading

When the leaves are completely brown they can be pulled gently and will come away cleanly from the corm, rather than leaving stubs sticking out of the ground. You can cut faded flowers at the base of the stem, but the seedheads offer structure and interest through winter. The plant should be cut to ground level in early spring before the new foliage emerges.

Dividing

Crocosmia corms multiply each year and clumps can become congested, leading to reduced flowering and vigour. Established plants can be lifted and divided every 3 to 4 years. Carefully separate the corms and replant the top-most corms, which will produce vigorous plants for the coming season.

Overwintering

Crocosmia hardiness varies according to species, but here in Sussex I leave all of mine in the ground in winter, giving them a good, deep mulch before the autumn frosts. In frost pockets, lift the corms in autumn and store them over winter in a frost-free place to plant again in mid-spring. With those left in the garden, note the deadheading advice, and cut to ground level in early spring before the new foliage emerges.

What to grow with crocosmia

For a warm display, try alongside a sunshine yellow gaillardia or peachy orange Coreopsis lanceolata. And for shorter varieties, crocosmia ‘Lucifer’ looks good among Verbena bonariensis and tall dark dahlias.

Pests, diseases & common issues

Red spider mite

These microscopic spiders are really hard to spot until the infestation has built up, which is most likely to occur during hot, dry summers. Possible signs include silvery webbing under the leaves as well as symptoms on the plant, including mottled colouring on leaves. Spray foliage with water to help reduce the chance of spider mites.

Why is my crocosmia not flowering?

If your crocosmia plants have been in the ground for a few years, the multiplying corms may have become congested. Lift and divide them to improve vigour. Crocosmia also need a good deal of sun to flower well, so ensure a sunny and sheltered position.

Why are my crocosmia leaves turning brown?

It could be gladiolus rust, which is a fungal disease that can affect crocosmia, particularly in humid conditions. Symptoms include brown or yellow spots on the underside of the leaves. Remove any affected leaves as soon as you spot them.

Why do my crocosmia not stand up straight?

After a few years, taller varieties of crocosmia can form large clumps and the plants have a tendency to flop if they become congested or are in an exposed, windy site. Lift and divide clumps that have become too big or consider staking tall varieties.

Is my crocosmia suffering from rot?

Waterlogged soil can lead to crocosmia corms succumbing to bacteria and rot. Make sure soil is well-drained and the plants are in a sunny position.

Photography by

Jonathan Buckley

Frequently asked questions

Is crocosmia invasive?

It can take a year or two for crocosmia to establish, and some (such as Crocosmia × crocosmiiflora) can become invasive over time.
How tall do crocosmia grow?

Some varieties grow up to to 1.2m (4ft), but you can find shorter varieties, such as crocosmia 'Peach Sunrise' which grows up to 60cm (2ft).
Are crocosmia deer resistant?

Yes, crocosmia is known to be deer resistant.
Do crocosmia spread?

Crocosmia corms multiply and spread each year. Make sure to lift and divide congested clumps every few years.
When should you cut back crocosmia?

Cut back crocosmia in spring to encourage vigorous growth.
Are crocosmia best in sun or shade?

Crocosmia are best in full sun but will tolerate light shade.
How deep should you plant crocosmia corms?

Plant corms in light, well-drained soil about 10cm (4in) deep.
How long does it take for crocosmia bulbs to sprout?

It takes around 4-6 weeks for shoots to emerge.
Is crocosmia poisonous to humans?

Crocosmia is potentially mildly harmful to humans and pets.

How to cut and arrange Crocosmia

Cut crocosmia stems early in the morning, cutting right at the base of the stem. Plunge into cold water and leave for a few hours before arranging. Crocosmia lasts up to 14 days in water – refresh every few days and add a splash of vinegar to the vase water to reduce the build up of bacteria.

Common name	Montbretia
Latin name	Crocosmia
Type	Perennial
Height	60cm (2ft) to 1.2m (4ft)
TLC rating	Easy
Aspect	Full Sun
Planting position	Back and middle of border
Suitable for pots	Yes
Good for pollinators	Yes
Good for cut flowers	Yes