Dahlias were neglected for many years, mostly loved by hobbyists who collected, grew and displayed them, but since the 90s they have rightfully made a comeback as a prominent presence in gardens.
Factors include smaller plants suited to modern gardens, colorful foliage to add variety to flower beds, single-flowered dahlias that are pollinator-friendly, and perhaps most importantly, the rise of home-grown cut flowers.
Cut dahlias are not suitable for transport and home-grown dahlias are superior: they follow the roses in the garden and bloom remarkably and profusely from August until the frosts of October.
Read next
Dahlias are native to the mountainous regions of Mexico and Central America, where summer temperatures are warm but not hot during the day and cool at night. Sound familiar?
Although they cannot tolerate frost, the tubers will dry out (but not dry out) and go dormant if kept in a cool (but not cold, freezing) place. This is fine for the dry, cool winters of their native range, but in the UK tubers left in the soil at this time of year are at risk in our wet, cold winters. For risk-averse gardeners, indoor storage over winter is recommended.
Start new dahlia seedlings by planting dormant tubers in April, or take cuttings from tubers that have been encouraged to grow in a warm greenhouse in late winter, or sow seeds in early spring for economical and easy growth. Bedding dahlias are usually grown from seed. Plants are offered as cuttings rooted in the spring or in small pots.
In summer, garden centers sell larger plants for gardeners who want to fill gaps in flower beds or revitalize pots where the flowers have died out. They're usually good value because, once fertilized and the flowers are removed, they'll bloom for a few weeks and can be stored until next year.
Many gardeners remove early blooming flowers before or after planting to encourage dahlias to develop a sturdier structure rather than a flowering plant. Dahlias flower (form tubers) when the days are short and the nights are long, and therefore tend to flower early, blooming profusely as fall approaches and producing fewer midsummer flowers.
Dahlias grow well in almost any sunny soil or in a pot, but they do best when watered and fertilized. Ideally, they should be planted in soil that contains well-composted compost or manure. Larger plants will need to be supported by stakes or netting.
Dahlias grow well in the UK (Photo: RHS/Nicola Stocken)
Deadheading encourages continued flowering. Gardeners who want larger flowers for cut or display may remove the top two side branches on each branch to prevent flowering, while those who want an abundance of small flowers may “pick off” the top buds early.
Few flowers are as varied as dahlias: The National Dahlia Society lists an astonishing 15 different flower forms: bronze, flame, dark red, lavender, lilac, orange, pink, purple, red, rose, white, wine, violet and yellow.
Those planning their 2025 flowers can visit the many dahlia shows running through the fall to see the incredible diversity and take notes, then order rooted cuttings or dormant tubers to arrive next spring.
For cut flowers, cut when the flowers are half open, early in the morning, in cool weather and with plenty of water. In a vase they will last 3-5 days.
When the plants have died back from autumn frosts, cut the stems and leave them covered around the base of the plant for two weeks, then dig up the tubers and dry them in a well-ventilated shed for two weeks, pack them in boxes with dry potting soil and store them in a frost-free place until spring.
