Dahlias / growing notes
When do dahlias bloom?
Dahlias usually bloom from midsummer into fall and keep flowering until frost. The planting date and your local frost season affect how long you can enjoy the flowers.
- When to plant
- Plant outdoors after the risk of frost, once the soil has stayed around 60°F (16°C) or warmer for several days.
- Sun and soil
- Give dahlias at least six hours of direct sun and soil that drains well.
- Water
- Established plants need regular water during dry weather. Pots need checking more often than garden beds.
- Winter care
- Tubers need protection where the ground freezes. Dig them up in fall and store them somewhere cool and frost-free.
Bloom timing and local weather
Which months?
Many garden dahlias begin flowering around mid-July and continue until frost. Your first flowers may come earlier or later. The planting date and local growing conditions affect the timing.
An earlier start
You can start tubers in pots indoors before outdoor planting time. Give the shoots bright light and keep them protected from frost. Move them into the garden after the local risk of frost has passed.
What ends the season
Dahlias flower through summer and fall, but freezing conditions damage their growth. Plan winter protection before that happens. A longer frost-free season gives the plants more time to flower.
Planting dahlias
Wait for warm soil
Cold, wet ground is a poor place for a dormant tuber. Wait until soil stays around 60°F (16°C) or warmer for several days. Choose loose, well-drained soil so water does not collect around it.
Keep the growing point facing up
Lay the tuber on its side in a hole about 4 to 6 inches deep, with its eye facing up. The eye is the small growing point near the crown. Allow about 2 feet between plants.
Growing in a pot
Dahlias can grow in containers with drainage holes and a good potting mix. Start tubers in pots indoors if spring is still cold. Keep the new growth protected until outdoor conditions are suitable.
Watering and supporting dahlias
Water established plants deeply
When rainfall totals less than an inch in a week, established dahlias generally need extra water. Water deeply during dry weather. Adjust for your soil so the roots stay moist without sitting in water.
Check pots more often
Container plants dry out faster and need regular watering through the growing season. In hot, dry weather, check them frequently. Keep the pot draining freely so the tubers are not left in soggy soil.
Put supports in early
Install a stake before planting to avoid pushing it through the tuber later. Tie the stems as they grow, supporting the lower stalk first and the branches as they get taller. A tomato cage is another option.
Keeping dahlias flowering
Remove faded flowers
Check the plant each week and remove spent flowers. Follow the stem down to a leaf joint and make the cut above it. This keeps the plant putting its energy into more flowers instead of seeds.
Leave fresh buds alone
A new dahlia bud is usually round. After a flower loses its petals, the spent head looks more pointed. Look at the shape before cutting so you keep the next flowers on the plant.
Pinch young plants for more branches
When a plant is about 12 to 16 inches tall and has at least four pairs of leaves, pinch out the growing tip above the top pair. This encourages a bushier plant.
Storing and dividing dahlias
Lift tubers after frost
In a cold-winter garden, wait several days after a hard frost, then cut the stems back and carefully dig up the tuber clump. Shake off loose soil, clean the tubers, and let them dry to the touch.
Store somewhere cool
Keep the dry clumps in a box with vermiculite or wood shavings. Store them somewhere dry and cool, around 40 to 50°F (4 to 10°C). The tubers must stay protected from freezing.
Divide in spring
To make more plants, split an overwintered clump in spring when you can see the new buds. Each piece needs a bud and attached tuber. A loose root without a growing point will not become a new plant.