Perennial Bulbs Overview: Dahlias

dahlia

Discover how to grow Dahlias with instructions on starting seed, transplanting, site selection, care and maintenance, water and fertilization requirements, and  pests and diseases.

Dahlias Stats at a Glance

Botanical Name: Dahlia sp.

Height: 20-24”

Soil Conditions:  Well-drained, deep, fertile soil

Sun: Full sun

Soil pH Conditions: 6.0-6.5

Planting Instructions

When Do I Plant Dahlias?

Dahlias are cold sensitive and should not be planted until after the last frost and the soil has reached at least 50°F.  They will germinate much more quickly in warmer soil.  You can hasten the warming of the soil with black plastic mulch. Planting in colder soil may result in dormant tubers that are more prone to rot.

Soil Temperature: 50°F

 

Where Do I Plant Dahlias?

Dahlias plants perform best in loamy, well-drained soil high in organic matter. Incorporating several inches of organic matter into the soil when preparing the bed will improve growth and development.

Soil Conditions:  Well-drained, deep, fertile soil
Sun: Full sun
Soil pH Conditions: 6.0-6.5

 

How Do I Plant Dahlias?

Dahlias can be propagated by direct planting or division.

Direct planting.  To plant tubers directly in the garden, dig a hole 6” deep.  Plant one tuber per hole in a horizontal position with the eye facing skyward.  Cover with a few inches of soil.  Add additional soil as the plant grows until the hole is filled in.

If you overwintered your bulbs from the prior year, you will want to start them indoors 6-8 weeks prior to planting out of doors.  Once you retrieve your roots from storage, discard any rotted or damaged sections.

You will need to cut the rhizomes into sections that contain one healthy root and one healthy eye.  Let these new pieces dry out for a day before planting.  Give each root its own container.

 

Division. If you live in a climate with mild winters and your dahlia plants overwintered outdoors successfully, divide crowded plants in the spring.

 

 

Can I Start Dahlias Indoors?

If you want earlier blooms, start your dahlias indoors.  Dahlias require fertile soil, moisture, good drainage, and plenty of room to grow, so choose your planting container accordingly.

Choose a pot that is at least 6” around and has plenty of drainage holes.  Line the bottom of the pot with pebbles and place on a saucer.  Fill the pot with a fertile commercial soil.  Plant the rhizome at a depth of about 3”, laying it horizontally with its eye facing up. Water thoroughly allowing any excess water to drain into the saucer.  Move to a warm, sunny location.  Keep the soil moist by watering from the bottom through the saucer.

 

Fertilize at least once with a 10-10-10 fertilizer.

 

When to Start Seeds: 6-8 weeks prior to planting
Time to Germination: 7-21 days
Light/Darkness Requirements: Dark
Optimal Temp. for Germination: 70-85°F

 

 

How Far Apart Do I Plant Dahlias?

To ensure good air circulation, space Dahlias 12” apart.

Dahlias Plant Care and Maintenance

How Often Should I Water Dahlias?

The key to watering Dahlias is to maintain a consistent moisture level. The soil should be moist to a depth of 6”.

Water the soil around the plant. Overhead watering will encourage disease.  Drip irrigation is best.

Mulch around the plant will help to lock in moisture.

 

Should I Fertilize Dahlias?

Fertilizing decisions should be based on a soil test.  If a soil test cannot be obtained you can fertilize your perennial bulbs will likely benefit from a once a month feeding with granular bulb fertilizer.  Fertilize more frequently (every other week) if using a water-soluble fertilizer.

Dahlia plants are heavy feeders and perform well with a high nitrogen fertilizer until flower buds appear. Follow with a high potassium fertilizer after budding.

Fertilize the soil around the plant at least 6” from the plant base. Irrigate into the soil.

 

Additional Care Instructions

For new plantings and division, pinch back the young plants when they have four sets of leaves to encourage bushiness and flowering.

Deadhead spent flowers to encourage continual blooming.

After the first frost, cut back the foliage to 6”, dig up tubers and bring indoors.

Can Dahlias Overwinter

As a tender perennial, Dahlias will not survive cold harsh winters.  If you want to save your flowers to replant next year, you will need to dig them up and store them for the winter.  When the foliage begins to die back following the first frost of the season, cut back the stems.  Gently loosen the soil around the clump of roots and remove from the soil.

Place the unwashed roots in a mesh bag filled with moist (not wet) peat moss and hang it in a dark, cool location.  Pack them lightly so that they receive good air circulation.  The peat moss should not be allowed to dry out or freeze during storage.

Dahlias Diseases

The most common diseases associated with this plant include blossom blights, crown gall, dahlia mosaic viruses, fungal leaf spot, gray mold, impatiens necrotic spot, smut, soft rot, and tomato spotted wilt virus.

Dahlias Pests

The most common pests associated with this plant include aphids, capsids, caterpillars, cucumber beetles, earwigs, flower thrips, planthoppers, slugs and snails, spider mites, and stem borers.

 

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