Dahliaknol

Dahlia pinnata

Engels: Dahlia Tuber

bulbAsteraceae

Dahliaknol (Dahlia pinnata) is a bulb from the Asteraceae family that grows up to 120cm tall. This plant thrives in full sun and requires moderate maintenance. Blooms in summer and late summer and autumn with red, orange, yellow, pink, white, purple flowers and attracts bees and butterflies.

Hoogte

40–120 cm

Breedte

40–60 cm

Zonligging

full sun

Waterbehoefte

moderate

Grondsoort

loam, sandy soil

Onderhoud

moderate maintenance

Bloeitijd

summer, late summer, autumn

Bloemkleuren

red, orange, yellow, pink, 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

Dahlia tubers are tender perennials that must be planted after all risk of frost has passed, typically from late April through May in temperate Europe. Choose a spot in full sun with well-drained soil—dahlias tolerate loam and sandy soils well but will rot in waterlogged conditions. Before planting, dig over the bed to a spade's depth and work in plenty of well-rotted compost or manure to improve structure and fertility. Plant tubers horizontally about 10–12 cm deep with any visible shoots or "eyes" pointing upwards. If your tuber has no obvious shoots yet, lay it flat; new growth will emerge from the crown. Space tubers 40–60 cm apart depending on the variety's mature spread—larger dahlias need more room. For taller cultivars (above 80 cm), insert a sturdy cane or stake at planting time, positioning it just behind the tuber to avoid damaging it later when roots have spread. Water the tubers in lightly after planting, then hold back on watering until you see shoots emerging above the soil; overwatering dormant tubers encourages rot. Once growth appears, water more regularly, especially during dry spells. Apply a 5 cm layer of mulch around the base to conserve moisture and suppress weeds, but keep it clear of the stem to prevent collar rot. In colder parts of zones 8–9, consider planting a few weeks later or covering the soil with fleece if a late frost threatens. Dahlias grow quickly once temperatures warm, so patience in spring pays off with vigorous plants by midsummer.

Pruning

Dahlias don't require traditional pruning in the sense of cutting back woody growth, but regular deadheading and pinching are essential for a long, prolific flowering season from summer through autumn. The database lists no specific pruning months because the work is ongoing throughout the growing season rather than a one-off annual task. When plants reach about 30–40 cm tall in early summer, pinch out the growing tip just above the third or fourth set of leaves. This encourages the plant to branch out lower down, resulting in a bushier shape and many more flowering stems. Without this pinch, dahlias tend to grow tall and leggy with fewer blooms. Deadheading is crucial from the moment the first flowers fade, usually by mid-July. Remove spent blooms every few days by cutting back to the first set of healthy leaves or a side bud. Use clean secateurs or simply snap off faded flowers by hand if stems are still soft. Prompt deadheading prevents the plant from setting seed, which diverts energy away from producing new buds. Left unchecked, flowering tails off significantly by late summer. In autumn, after the first hard frost blackens the foliage, cut stems down to about 15 cm above ground level. Carefully lift the tubers with a fork, shake off excess soil, and allow them to dry for a few days before storing in a frost-free place over winter. In milder zone 8–9 gardens you may leave tubers in situ under a thick mulch, but lifting and storing indoors is safer and prevents rot during wet winters.

Maintenance

Dahlias have moderate water needs but perform best with consistent moisture during active growth and flowering. Water deeply once or twice a week from late spring through summer, increasing frequency during hot, dry spells—plants in sandy soils will need more frequent watering than those in loam. Avoid overhead watering, which encourages powdery mildew and botrytis; instead, water at the base. Reduce watering in autumn as flowering slows and foliage begins to decline. Feed dahlias regularly to fuel their long flowering season. The database indicates March feeding, which applies to stored tubers being prepared for planting; dust them lightly with a general-purpose fertiliser before potting up indoors for an early start. Once planted out and actively growing, switch to a high-potassium liquid feed (such as tomato fertiliser) every two weeks from early July until late September. Avoid high-nitrogen feeds after midsummer, as these promote leafy growth at the expense of flowers. Dahlias are hardy only to zone 8a and will not survive frozen soil. In most of temperate Europe, lift tubers in November after frost blackens the foliage, dry them off, and store in barely damp compost or vermiculite in a cool, frost-free shed or garage. Check stored tubers monthly and discard any showing signs of rot. Common pests include slugs and snails, which devour emerging shoots in spring—use barriers, traps, or pellets around young plants. Aphids cluster on buds and soft growth; squash by hand or spray with soapy water. Earwigs can damage petals; trap them in upturned pots stuffed with straw. Powdery mildew may appear in dry summers; ensure good air circulation and water at soil level to minimise risk.