Dahlia

Dahlia x hortensis

perennialAsteraceae

Dahlia (Dahlia x hortensis) is a perennial from the Asteraceae family that grows up to 150cm tall. This plant thrives in full sun and requires regular maintenance. Blooms in summer and late summer and autumn with red, pink, orange, yellow, white, purple flowers and attracts bees and butterflies.

Hoogte

40–150 cm

Breedte

40–80 cm

Zonligging

full sun

Waterbehoefte

moderate

Grondsoort

loam, sandy soil

Onderhoud

high maintenance

Bloeitijd

summer, late summer, autumn

Bloemkleuren

red, pink, orange, yellow, white, purple

Ecologische waarde

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Verzorgingskalender

Taak	Jan	Feb	Mrt	Apr	Mei	Jun	Jul	Aug	Sep	Okt	Nov	Dec
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Care tips

Planting

Dahlias thrive in full sun and need at least six hours of direct sunlight daily to produce their best blooms. Choose a sheltered spot protected from strong winds, as the tall stems can be brittle. They prefer well-drained loam or sandy soil enriched with plenty of organic matter. Before planting, dig over the soil to a spade's depth and work in a generous amount of well-rotted compost or manure to improve both drainage and fertility. Plant dahlia tubers from March to May once the risk of hard frost has passed, typically late April or early May in most of temperate Europe. You can also plant in September or October in milder areas, though spring planting is more reliable. Dig a hole about 12–15 cm deep and place the tuber horizontally with any visible growing points or "eyes" facing upwards. Space tubers 60 cm apart to allow for their mature spread and good air circulation. For taller varieties over 90 cm, insert a sturdy stake at planting time to avoid damaging the tuber later. Cover the tuber with about 5 cm of soil initially, then fill in the rest as shoots emerge. Water sparingly at first—overwatering dormant tubers can cause rot. Once shoots appear and growth is underway, water more generously. Apply a 5 cm layer of mulch around the base to retain moisture and suppress weeds, but keep it clear of the emerging stems. In colder zones, consider starting tubers indoors in pots during March and transplanting outside in May after hardening off.

Pruning

Dahlias benefit from regular pruning throughout the growing season to encourage bushier growth and more abundant flowering, though the main structural pruning happens in March and November. In March, before new growth begins, inspect overwintered tubers and cut away any soft, rotten, or damaged sections with a clean, sharp knife. If you're dividing clumps, ensure each division has at least one viable eye. During the growing season—typically June onwards—pinch out the growing tip when plants reach about 40 cm tall. Remove the top set of leaves and the growing point just above a leaf node. This encourages the plant to produce side shoots, resulting in a bushier shape and more flower stems. For exhibition-quality blooms, practice disbudding: remove the two smaller side buds that flank the main terminal bud on each stem, directing all energy into one large flower. For garden display, this isn't necessary. Deadheading is essential throughout summer and autumn. Remove spent blooms every few days by cutting back to the next leaf joint or side shoot. This prevents seed formation and keeps the plant flowering prolifically until the first frosts. In November, after frost has blackened the foliage, cut stems down to about 15 cm above ground level. Carefully lift the tubers with a fork, taking care not to damage the delicate necks. Brush off excess soil, trim away remaining foliage, and allow tubers to dry before storing.

Maintenance

Dahlias have moderate to high water needs, especially during active growth and flowering. Water deeply two or three times weekly during dry spells in summer, aiming to keep the soil consistently moist but never waterlogged. Reduce watering in early autumn as flowering slows. Avoid overhead watering, which can encourage powdery mildew and botrytis; instead, water at the base of the plant. Feed dahlias regularly to support their long flowering season. In March and April, as shoots emerge, apply a balanced granular fertiliser or one slightly higher in nitrogen to promote leafy growth. Once flower buds form in early summer, switch to a high-potassium liquid feed (such as tomato fertiliser) every two weeks until September. This encourages abundant blooms and strong tuber development for next year. Dahlias are not reliably hardy in most of temperate Europe (zones 7–9). In November, after the first frost, lift tubers carefully and store them in a frost-free place over winter. Pack them in barely moist compost, sand, or vermiculite in a cool, dark shed or garage at around 5–10°C. Check monthly and discard any that show signs of rot. Common pests include slugs and snails, which can devastate young shoots in spring—use barriers, traps, or organic pellets. Earwigs may damage petals; trap them in inverted pots stuffed with straw. Aphids cluster on buds and shoot tips; squash by hand or spray with soapy water. Powdery mildew can appear in dry conditions; ensure good spacing and water at soil level. Remove and destroy any foliage affected by virus, which causes stunted growth and mottled leaves.