Dahlia Growing Guide
Dahlia pinnata
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
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