The Complete Dahlia Growing Guide
Everything you need to know to grow stunning dahlias — from choosing your first tubers to storing them for next season. Written by experienced growers, backed by ADS standards.
In This Guide
Choosing Varieties
Selecting the right dahlias starts with understanding your goals. Are you growing for cut flowers, garden impact, or competitive showing? Each path favors different bloom forms and sizes.
For cut flowers: Look for long-stemmed varieties in the formal decorative, cactus, and waterlily forms. Café au Lait, Cornel, and Labyrinth are industry favorites with excellent vase life (7–10 days). Aim for medium to large sizes (B and A classes).
For garden borders: Consider compact varieties under 3 feet. Mignon singles, pompons, and ball dahlias create stunning mass plantings. Mix bloom times for continuous color from July through frost.
For showing: Study the ADS classification system carefully. Judges score on form, size (relative to class), color, and condition. Start with proven show varieties like AC Rooster, Hamari Gold, or Inland Dynasty and grow at least 3 plants per variety for selection.
Whatever your goal, start with 5–10 varieties your first year and expand from there. Buy from reputable nurseries that ship healthy, labeled tubers — check our Grower Directory for vetted sources.
Planting & Soil
Dahlias demand full sun — a minimum of 6 hours, ideally 8. Morning sun with afternoon shade is acceptable in hot climates (zones 9–10), but northern growers should maximize exposure.
Soil preparation is non-negotiable for great dahlias. The ideal mix is loose, well-drained, and slightly acidic to neutral (pH 6.0–7.0). Heavy clay needs amending with compost and coarse sand at a 1:1 ratio. Sandy soils need organic matter for water retention.
Plant tubers horizontally, 4–6 inches deep, with the eye (growing point) facing up. Spacing depends on size class:
- Dinnerplate (AA): 24–30 inches apart
- Large/Medium (A, B): 18–24 inches apart
- Small/Miniature (BB, M): 12–15 inches apart
Critical tip: Stake at planting time. Drive a 4–5 foot stake next to each tuber before backfilling. Trying to stake a mature plant in August risks spearing the root cluster.
Timing varies by zone: Zones 3–5 plant late May; Zones 6–7 mid-April; Zones 8–9 March; Zone 10 February or year-round.
Watering & Feeding
After planting, water thoroughly once — then stop until green shoots emerge. This is the most common mistake new growers make. The tuber contains enough moisture to initiate growth, and overwatering dormant tubers causes rot.
Once growth is active, dahlias need about 1 inch of water per week. Deep, infrequent watering is far better than frequent light sprinkles. Drip irrigation or soaker hoses are ideal — avoid overhead watering, which promotes fungal disease.
Feeding schedule:
- At planting: Incorporate bone meal or a balanced organic fertilizer into the planting hole
- Once shoots emerge: Begin feeding every 2–3 weeks with a low-nitrogen fertilizer (5-10-10 or similar). High nitrogen produces lush foliage at the expense of blooms
- Mid-season: Switch to a bloom-boost formula (0-10-10) once buds begin forming
- Late season: Stop feeding 4 weeks before your expected first frost to help tubers harden off
Mulch with 2–3 inches of straw or shredded bark to retain moisture and suppress weeds. Keep mulch a few inches away from stems to prevent rot.
Cutting & Deadheading
The more you cut, the more dahlias bloom. This isn't a cliché — it's how the plant works. Removing spent blooms and cutting fresh ones redirects energy from seed production into new bud development.
Pinching: When plants reach 12 inches tall, pinch (cut) the center growing tip just above a leaf node. This single act encourages lateral branching and can double your bloom count. It delays first blooms by 2–3 weeks, but the payoff is dramatic.
Disbudding: For show-quality or large blooms, remove the two side buds that flank each terminal (center) bud. This directs all energy into one magnificent flower. Skip this if you want volume over size.
Cutting for vase: Harvest in the morning when stems are full of water. Cut when blooms are about three-quarters open. Use sharp, clean snips. Immediately place stems in hot (not boiling) water — 160°F — for one hour, then move to cool water. This "hot water treatment" can extend vase life to 7–10 days.
Deadheading: Remove spent blooms promptly. The "dead" flower looks like a cone — don't confuse it with a bud, which is round. Snip deadheads back to a lateral branch or leaf node.
Pests & Disease
Dahlias are generally robust, but a few common issues can derail a season if left unchecked.
Slugs and snails are the number-one enemy of young dahlia shoots. Protect emerging growth with iron phosphate bait (pet-safe), copper tape around pots, or beer traps. Once plants are 12+ inches tall, slug pressure drops dramatically.
Aphids cluster on new growth and buds. A strong spray of water dislodges most of them. For persistent infestations, neem oil or insecticidal soap works well. Encourage ladybugs and lacewings — a single ladybug eats up to 50 aphids per day.
Powdery mildew appears as white patches on leaves in late summer, especially in humid climates with poor air circulation. Prevention is key: space plants adequately, water at soil level (not overhead), and ensure good airflow. Treat with a milk spray (1 part milk to 9 parts water) or potassium bicarbonate fungicide.
Dahlia mosaic virus (DMV) causes stunted growth and mottled leaves. There is no cure — infected plants should be removed and destroyed. Buy from reputable sources that test for virus. Don't propagate from infected stock.
Earwigs chew petal edges at night. Trap them with rolled newspaper placed near plants overnight — collect and dispose in the morning.
Overwintering & Storage
In zones 8–10, dahlias can often overwinter in the ground with a heavy mulch layer (6–8 inches of straw). In zones 7 and colder, you must dig and store tubers to survive the winter.
When to dig: Wait until a hard frost blackens the foliage, then cut stems to 4–6 inches. Carefully dig the clump with a garden fork, working 12 inches out from the stem to avoid slicing tubers. Let the clump dry in a sheltered spot for 24 hours.
Dividing: You can divide in fall or spring. Each division needs at least one eye (growing point) attached to a tuber with some of the crown. Use a sharp, clean knife. Let cuts callus for 24–48 hours before storing.
Storage methods — choose what works for your climate:
- Vermiculite in paper bags: The most popular method. Fill bags loosely, store in a cool (40–50°F), dark location
- Plastic wrap: Individually wrap each tuber in cling film. Prevents dehydration in dry climates
- Peat moss in bins: Layer tubers in slightly damp peat moss in ventilated bins
- Wood shavings: Clean pine shavings in cardboard boxes. Check monthly for mold
Check stored tubers monthly. Remove any that show signs of rot (soft, mushy) to prevent spread. Lightly mist if tubers appear shriveled. The goal is cool, dark, and slightly humid — not wet.
In spring, bring tubers into warmth and light 4–6 weeks before your planting date to "wake them up" and check for viable eyes.
Ready to Start Growing?
Browse our variety directory to find the perfect dahlias for your garden, or find a trusted nursery near you.