How to grow chrysanthemums

What are chrysanthemums?

Chrysanthemums are probably most familiar as cut flowers, but they are also eye-catching and versatile garden plants. They add colour to borders and containers in late summer and autumn, when many other plants are past their best.

There are many types of chrysanthemums, but here we focus on 'early' or 'hardy' garden chrysanthemums. These are widely available, straightforward to grow, and flower abundantly outdoors in late summer and autumn. Although they are generally classified as hardy, it is still best to protect them from frost. Chrysanthemums are perennials, going

Dormancy refers to a period of inactivity in plants, during which they slow down or stop their growth, conserving energy and resources. This is a natural process that helps them survive harsh conditions, such as winter or drought. Dormancy in seeds is a mechanism that prevents them germinating until environmental conditions are favourable for growth.

How and what to buy

Hardy chrysanthemums are available from garden centres and mail-order suppliers. Plants can be bought at various sizes:

• Newly rooted cuttings or young plants are available in spring. These small plants must be looked after indoors until large enough to plant outside, after the last frost. So you need space on a cool, bright windowsill or in a frost-free greenhouse (see Planting below).

• Established young plants can be bought in early to mid-summer, for planting straight into borders or containers, where they will flower after just a few months. 

• Mature plants in full bloom are available in late summer and early autumn. These create an instant display in borders and containers. 

To explore the range of chrysanthemums, go to RHS Find a Plant. Search for ‘chrysanthemum’ to browse the photographs and plant descriptions, and find out where to buy them. You can refine your search by hardiness, to suit your local climate. 

Where to plant

• In a warm, sheltered, sunny location

• ​In borders, in most soil types

• In containers, especially dwarf cultivars

• In a dedicated cut-flower border, so you can pick lots of blooms without spoiling the display in the garden

Chrysanthemums suit many garden styles, formal or informal, traditional or contemporary. Those with vibrant flowers work particularly well in exotic plantings, the pastel shades mingle sociably in cottage-garden borders, while the warm, burnished hues complement ornamental grasses.

When to plant

Plants that have been stored in a light frost-free place over winter can be planted outside in late spring, after the last frost (typically from mid May to early June). 

Young plants raised from cuttings can be planted outside at the same time, once well rooted and growing strongly. Wait until after the last frost, having acclimatised them to outdoor conditions by hardening off few a few weeks beforehand.

Plants bought in summer can be put straight into borders and containers. If bought in late summer, they will be in full flower and provide instant colour.

How to plant

Chrysanthemums are easy to plant:

• Space plants 30–45cm (12–18in) apart

• Add a stake to support taller types

• When planting in containers, use peat-free John Innes No 2 compost and a container with a diameter of at least 30cm (1ft)

How to look after plants in containers

How to look after plants in containers

Pinching out (stopping)

Once young plants reach about 20cm (8in) tall, in early summer, pinch out the main growing point to encourage branching. You can also pinch out the tips of sideshoots as they grow, until about mid-summer. This will help to create stockier plants that will carry more flowers.

Watering

Newly planted chrysanthemums, in borders or containers, need regular watering through the growing season. Never let the soil or compost dry out completely. But take care not to overwater too, as they dislike waterlogged conditions.

Tips on recycling and collecting water

Tips on recycling and collecting water

Feeding

Plants growing in containers can be fed with an organic liquid seaweed fertiliser as per the instructions on the label. During flowering, switch to a high potassium fertiliser such as tomato feed.

Guide to fertilisers

Guide to fertilisers

How and what to feed plants

How and what to feed plants

Mulching

Apply a thick layer of mulch to the soil surface after planting. This will help to hold moisture in the soil and prevent weed germination. Use well-rotted manure or garden compost.

If leaving plants in the ground over winter, insulate the roots with a thick layer of mulch in late autumn. 

Removing some flower buds (disbudding)

Disbudding is a specialist technique used to produce very large blooms or well-balanced clusters to use as cut flowers or for exhibition:

• On 'spray' chrysanthemums – these produce clusters (sprays) of flowers. If you remove the large central flower bud, you'll get a more uniform display of evenly sized blooms.

• ​On single-flowered chrysanthemums – keep the main central flower bud and remove all the side buds and other shoots. The plant will then put all its energy into producing one spectacular flower.

Deadheading

Removing faded flowers regularly helps to keep the display looking its best. It also encourages new buds to form, extending the overall display.

See our guide to deadheading.

Overwintering

Most hardy chrysanthemums can survive temperatures down to at least -5˚C (23˚F). However, in much of the UK temperatures can fall below this, so it may be safer to lift and store plants over winter in light, frost-free conditions, such as a frost free greenhouse, a cool conservatory, porch or similar. Plants in exposed or poorly drained sites will particularly benefit.

• Once flowering has finished, cut down the stems to about 20cm (8in) tall, to produce what is known as a stool

• Lift the shortened plants and shake off the soil from the roots

• Snip off any green shoots and leaves, so you have bare stems

• Label each plant, if you have several different types

• Stand the stools in a shallow tray, on a 5cm (2in) layer of slightly damp compost. Cover the roots lightly with loose compost.

• Store in a cold but frost-free location, such as a cool greenhouse or conservatory, or a garage

• Keep the compost just moist through the winter

​

Moving plants into a conservatory

Moving plants into a conservatory

Overwintering plants by lifting or mulching

Overwintering plants by lifting or mulching

In mild regions

Where temperatures are unlikely to fall below -5˚C (23˚F), especially in sheltered gardens with well-drained soil, you could risk leaving plants in the ground through winter.

Even so, it's best to give them some protection:

• Cover the root zone with an insulating layer of mulch

• Consider using a cloche to protect plants from winter rain

In containers

Plants in containers are particularly vulnerable to cold, so bring them indoors once flowering has finished. Keep them frost free, such as in a cool greenhouse or enclosed porch.

In very mild regions, you could risk leaving them outside, in which case:

• Move them to a warm, sheltered spot, such as in the lee of a wall or under the eaves

• Wrap containers in insulating layers of biodegradable fleece, to protect the roots.

• Make sure the compost doesn't get waterlogged – stand containers on bricks (or pot feet) to keep the drainage holes clear

​

How to look after plants in containers

How to look after plants in containers

Protecting plants in winter

Protecting plants in winter

Once flowering is over in late autumn, cut the whole plant down to 20cm (8in) tall. See our guide to cutting back perennials in autumn.

The easiest way to make new plants is by taking cuttings in spring and to divide clumps. It's also possible to grow a few chysanthemum from seed.

By cuttings

In spring, use the vigorous new shoots as basal softwood cuttings. These root quickly and reliably to form plants that will flower in late summer:

• Remove several shoots, 5–7.5cm (2–3in) long, from the outside of a clump. Cut with a sharp knife, right at the base, as close as possible to the crown

• Remove the lower leaves and insert the cuttings into pots containing a mix of half peat-free multipurpose compost and half horticultural grit. Water in, then place in a propagator. Put in bright light (away from direct sunshine), at 10°C (50°F) or above

• Ensure the compost is always moist, but not soggy, to encourage rooting

• They should root in about three weeks. Move them into larger pots as they grow

• They should be ready to plant out in a couple of months. Wait until after the last frost, harden them off carefully, and protect from slugs and snails

Plants that are in winter storage can be started into growth earlier than normal, so they produce shoots ahead of outdoor plants. Cuttings taken from these can have a head-start of several months:

• In early January, bring plants out of winter storage into a greenhouse at 7–10°C (45–50°F)

• Water them so the compost is thoroughly damp, then keep it just moist

• Within three or four weeks, from mid-February, you should have large enough shoots to use as cuttings. Follow the method outlined above

By division

Older plants tend to lose vigour over time, so can be divided in spring, once growth has started. See our guide to dividing perennials.

By seed

A few cultivars are available as packeted seeds. Sow in spring at 15°C (59°F). They should germinate within two weeks, and the resulting plants should flower in the same year.

Pests

Chrysanthemums are susceptible to several pests, although most only do superficial damage. Check plants regularly and remove any pests as soon as they appear. Look out for:

• Slugs and snails – take care to protect young plants

• Aphids 

• Leaf miners 

• Leaf and bud eelworms 

• Earwigs 

• Capsid bugs 

• Red spider mites

Diseases

Chrysanthemums can be affected by several diseases, especially when their growing conditions aren't ideal. These include:

• Chrysanthemum white rust – can be very damaging and hard to control 

• Powdery mildew – prevalent in dry conditions

• Grey mould and other fungal rots – thrive In wet weather 

• Viruses – cause stunted growth and leaf markings

How to control pests and diseases without chemicals

How to control pests and diseases without chemicals

Guide to preventing pests and diseases

Guide to preventing pests and diseases