How to grow Dahlia

Dahlia × pinnata · Dahlia pinnata, garden dahlia

Tender tuberous perennial grown for its varied, showy flowers from midsummer until frost. Tubers go in when the soil has warmed in late spring; first flowers come about 90–100 days after planting. Mildly toxic to cats, dogs and horses.

Quick facts

Type	Flower
Family	Asteraceae
Light	Full sun
Soil pH	6.5–7
Frost	does not tolerate frost
Soil for sowing	from 16 °C
Germination	21 days
Where it grows	Open ground

When to plant

Sow straight into the bed after your last spring frost, once the soil has warmed.

Frost dates · When to plant

Care

Open ground

Stage	Watering	Temperature	Feeding
Growth	every 7 days	—	phosphorus and potassium, 20 days into the stage; phosphorus and potassium, 45 days into the stage
Flowering	every 7 days	—	phosphorus and potassium, at the start of the stage; phosphorus and potassium, 25 days into the stage

Growing notes

Light

Full sun, at least six hours a day, for the most flowers.

Soil

Loose, fertile, well-drained soil with a pH of 6.5–7.0. Soggy soil rots the tubers.

Care

Plant when the soil has stayed around 16 °C for several days. Lay the tuber flat 10–15 cm deep with the eye facing up, about 60 cm apart, and set a 1.2–1.5 m stake beside it. Do not water until the first leaves appear, then keep the soil evenly moist, never soggy or dry. Pinch out the tip when plants are 30–40 cm tall. From 30 days after planting feed a low-nitrogen fertiliser such as 5-10-10 every 3–4 weeks, and stop in September. After a hard frost kills the stems, lift the tubers and store them dormant at 1–4 °C. Watch for aphids, earwigs, slugs and powdery mildew.

Pests and diseases of Dahlia

Sources

Figures checked against these sources.