Dahlia Growing Guide

Dahlia

Crop Rotation Group

Miscellaneous 

Soil

Rich, fertile soil with excellent drainage.

Position

Full sun.

Frost tolerant

None. Dahlia foliage is killed by frost, and roots are hardy only to about -9C (15F).

Feeding

Topdress with rich compost in early summer, after new growth appears. Fertilise with a liquid fertiliser in midsummer to support strong re-blooming.

Companions

Mint, Thyme, Coriander, Rosemary, Gladiolus and Echinacea. The bushy plants will crowd any close neighbors. Tall varieties that require staking should be grown behind smaller plants. Dwarf dahlias can be mixed with Asiatic lilies or repeat flowering roses.

Spacing

Single Plants: 60cm (1' 11") each way (minimum)
Rows: 50cm (1' 7") with 60cm (1' 11") row gap (minimum)

Sow and Plant

Dahlias are often sold as dormant crowns consisting of several connected tubers. Prepare a wide planting hole dug to at least 30cm(12 inches) deep, and generously enrich the holes with rich compost and a balanced organic fertiliser. Spread out the tubers and plant them 8cm(3 inches) deep. A few weeks later after the first stems emerge, hill up a little soil around the base of the plant and begin summer mulching. Allow 60cm (24in) between tall dahlias. Small dwarf varieties can be planted 30cm(12in) apart.
Our Garden Planner can produce a personalised calendar of when to sow, plant and harvest for your area.

Notes

Dahlias will bloom all summer when provided with regular water and fertiliser. The colour range is endless, and flower size can be large or small, depending on variety.

Harvesting

Dahlias make excellent cut flowers, so they should be easily accessible. Cut dahlias for arrangements as soon as the blossoms open, preferably in early morning. Immediately plunge the stems into warm water. As the flowers fade in the garden, trim them off with scissors or secateurs.

Troubleshooting

Numerous insects and diseases can plague dahlias. Promptly trim off badly damaged branches, and use insecticidal soap to manage thrips and whiteflies if necessary.

Planting and Harvesting Calendar

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Pests which Affect Dahlia