Chrysanthemum

Chrysanthemum × morifolium (Ramat.) Hemsl. · mums · chrysanths · florist's chrysanthemum · florist's daisy · hardy garden mum · garden mum · pot mum

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At a Glance

Overview

Chrysanthemum (Chrysanthemum × morifolium (Ramat.) Hemsl.) is the long-cultivated florist's chrysanthemum of UK autumn gardens: an herbaceous perennial in the daisy family Asteraceae whose late-season flowerheads carry most UK borders from late summer into November. The accepted scientific name, with the hybrid cross preserved, is Chrysanthemum × morifolium (Ramat.) Hemsl., and Kew's Plants of the World Online records it as an accepted hybrid whose native range is south-east China. The Royal Horticultural Society genus guide lists its common names as "Mums, chrysanths"; the species is more widely known in UK and US horticulture as the florist's chrysanthemum, the florist's daisy, the hardy garden mum, the garden mum, or the pot mum. The plant you may have bought under the older name Dendranthema × grandiflora (Ramat.) Kitam. is the same species — that name is a POWO-recognised heterotypic synonym that was used for decades in UK trade and still appears on the RHS Dendranthema grandiflorum synonym page, so the page subject stays Chrysanthemum × morifolium and the slug stays `chrysanthemum-morifolium`. The species is not native to Great Britain or Ireland. For companion planting in the late-winter garden slot that follows chrysanthemums in the calendar, the GardenWizz encyclopaedia entry for cyclamen coum is a natural partner.

Appearance

Chrysanthemum × morifolium is a clump-forming, sometimes bushy herbaceous perennial with a woody-based rootstock and aromatic, pinnately lobed leaves carried on upright stems; the RHS describes the genus as "erect woody-based perennials with aromatic, pinnately lobed leaves and flowerheads of diverse form, from late summer to late autumn." Mature plants reach the dimensions recorded for the RHS Award of Garden Merit cultivar set on the genus guide: 0.5–1.5 m tall by 0.1–1 m wide, depending on cultivar. The species is a hybrid complex whose individual cultivars vary considerably, so this article deliberately quotes dimensions as an envelope across the AGM cultivars rather than as a single species value. Flowerheads range from open single daisies through intermediate decorative forms to fully double pompoms, and the colour range covers pink, purple and red through orange, yellow and white. Leaves are deeply lobed, mid- to dark-green, and carry the distinctive aromatic scent that gives cut chrysanthemum stems their characteristic greenhouse smell. Flowering runs from late summer into November, with the RHS growing guide pinning the UK window as "in flower from September to November." This is the same plant sold in late summer as a flowering pot plant — those tender florist-grade "pot mums" are a different market and are not the focus of this hardy-garden-chrysanthemum entry.

Growing Conditions

Give chrysanthemums a warm, sunny and sheltered spot in fertile, moist but well-drained peat-free soil or compost; the RHS genus guide is explicit that they "enjoy a warm, sunny and sheltered spot" and "need fertile and moist but well-drained peat-free compost or soil", and that "most won't survive heavy frosts or waterlogged soil" and "don't perform well in dry conditions, poor soil or shade." In containers use a peat-free John Innes No 2 compost in a pot at least 30 cm (1 ft) in diameter, and mulch borders with well-rotted garden compost or manure to hold moisture and feed the roots. Water regularly through the growing season without ever letting the pot or border dry out completely, and avoid waterlogging at all costs — the RHS warns that chrysanthemums dislike waterlogged conditions as much as dry soil. Position is full sun in a sheltered border or south- to west-facing aspect; light afternoon shade is tolerated in hotter parts of southern England but reduces flower count. Chrysanthemums combine well with other autumn-flowering border plants such as salvias, sedums, asters and ornamental grasses, and they earn their place in a dedicated cut-flower border where sprays can be picked without spoiling the garden display.

Planting and Care

Plant out hardened-off young plants from mid-May to early June, once the last frost has passed in lowland Britain; the RHS growing guide says "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)". Space plants 30–45 cm (12–18 in) apart in the border, add a stake to support taller cultivars, and pinch out the main growing point once stems reach about 20 cm (8 in) tall in early summer to encourage branching; continue pinching the tips of sideshoots through to mid-summer for stockier, more floriferous plants. Water regularly in dry spells, feed container-grown plants with an organic liquid seaweed fertiliser through the growing season, and switch to a high-potash feed such as tomato fertiliser once flowering starts. Deadhead spent blooms to extend the display into November, then cut the whole plant down to about 20 cm in late autumn once flowering is finished. In most of the UK the stools need to be lifted: cut stems to around 20 cm, lift the clump, shake off the soil, label the variety, and stand the stools in a shallow tray on 5 cm of damp compost in a cold but frost-free greenhouse, porch or conservatory. In mild, sheltered regions a thick autumn mulch over the crown is often enough to carry plants through. Propagate new plants by taking 5–7.5 cm basal softwood cuttings in spring, inserting them into a 50:50 mix of peat-free multipurpose compost and horticultural grit in a propagator at 10 °C or above in bright, indirect light; they should root in about three weeks. Established clumps can also be divided in spring once growth has restarted.

Common Problems

UK chrysanthemums face a defined set of pests and diseases that the RHS growing guide lists explicitly: slugs and snails (most damaging on young spring growth), aphids on soft shoot tips, leaf miners (serpentine pale tunnels in leaves), leaf and bud eelworms (angular brown-black areas between leaf veins with distorted buds), earwigs (notched petals on doubles in late summer), capsid bugs (distorted young leaves), and red spider mite under hot dry conditions — especially in greenhouses and indoor overwintering. The four significant diseases are chrysanthemum white rust ("can be very damaging and hard to control", with pale spots on the upper leaf surface and white pustules underneath), powdery mildew in dry conditions, grey mould (Botrytis) and other fungal rots in wet weather, and viruses that cause stunted growth and leaf markings. Manage them by improving air circulation, watering at the base rather than overhead, mulching to keep roots moist, removing and binning (not composting) badly affected material, encouraging natural predators outdoors, and sourcing new stock from clean suppliers. In confirmed outbreaks of chrysanthemum white rust, contact the RHS or Defra Plant Health for current UK statutory guidance. Common sense checks: don't plant out before the last frost, don't let borderline-hardy cultivars sit in cold wet clay over winter, and don't overwinter in a warm dry room where red spider mite takes hold. On toxicity, the ASPCA records chrysanthemum as toxic to dogs, cats and horses, with toxic principles of sesquiterpene lactones and pyrethrins — the same chemistry that underlies natural pyrethrin insecticide extracted from chrysanthemum flowers; the RHS does not publish a species-level toxicity statement for Chrysanthemum × morifolium, so keep cut flowers and border plants out of reach of browsing pets and wash hands after handling. On hardiness, the RHS growing guide states that "most hardy chrysanthemums can survive temperatures down to at least -5 °C (23 °F)" and that the broader H4 rating of -10 to -5 °C applies to most of the hardy garden chrysanthemum group; the RHS does not pin a single H-code to the species row, so the practical UK guidance remains: lift and store stools in most regions, mulch heavily in mild sheltered gardens, and bring containers indoors for winter.

Popular Varieties

The RHS genus guide lists eight current Award of Garden Merit cultivars of Chrysanthemum × morifolium — 'Ruby Enbee Wedding' (29d), 'Cream Talbot Parade' (29c), 'Myss Saffron' (29c), 'Yellow Pennine Oriel' (29a), 'Ruby Raynor' (21c), 'Max Riley' (23b), 'Allouise' (25b), and 'Gold Enbee Wedding' (29d) — each with its own height, width, classification code, and colour range. This species-level encyclopaedia page deliberately does not own a cultivar table: detailed profiles of 'Ruby Enbee Wedding', 'Cream Talbot Parade', 'Myss Saffron', 'Yellow Pennine Oriel', 'Ruby Raynor', 'Max Riley', 'Allouise' and 'Gold Enbee Wedding' belong at their own future GardenWizz cultivar slugs, and no separate page is created for the older synonym Dendranthema grandiflora since that name points to the same plant covered here. The National Chrysanthemum Society maintains the formal UK classification system reflected in those AGM cultivar codes (the trailing digits refer to the flower section and colour group), and specialist nurseries sell cultivars organised by flower form — sprays, decoratives, pompons, singles, spiders and spoons — and by flowering window from late August through November. When buying, look for plants labelled "hardy garden chrysanthemum" or "early-flowering outdoor chrysanthemum" rather than tender florist-grade pot mums; the latter are raised for indoor display and rarely survive a UK winter outdoors. For a broad informal planting, mixed collections of unnamed AGM cultivars in complementary autumn colours give the most reliable UK display.

Pests and Diseases

For step-by-step help, read Controlling Aphids Naturally, Dealing with Slugs and Snails and Treating Powdery Mildew. Or browse the full plant problem solver to diagnose an issue by symptom.