Dahlias have showy petal-packed blooms in myriad shapes, sizes, and colors.
Originally native to Central and South America, today’s garden hybrids aretender perennialsthat grow from tuberous roots.
Dahlia fanciersdivide the flowers into many classes based on form.
Credit: Photo: Alison Miksch
Some plants grow to an impressive 6 feet tall.
Taller varieties need staking.
Adding compost to the plants on new growth will help produce the best blooms.
The more you feed dahlias, the more blooms they will produce.
These flowers can be grown in gardens and containers and should have regular watering.
Big-flowered kinds are the most heat sensitive.
Dahlias grow best in full sun with in light afternoon shade.
Soil
A dahlia plant prefers moist, well-drained soil that contains lots of organic matter.
Loamy and sandy soils are also good for growing dahlias.
In January and February, combine leaves and mushroom compost with the soil.
The soil should never be fully dry.
Many gardeners grow them as annuals.
Wait until the final spring frost passesto plant tubers.
Fertilizer
Use a fertilizer within the first 30 days of planting tubers to promote growth.
The more you fertilize dahlias, the more showy and numerous blooms.
Stop fertilizing plants when temperatures drop if you plan to keep dahlias over the winter.
Since fertilization promotes growth, you shouldn’t force new flowers during dormancy.
Use a bloom-boosting fertilizer that is low in nitrogen and high in phosphorus.
Some popular types of dahlias include:
Pruning
Dahlias needspecific pruningto encourage new blooms.
Pinch the flower tops after at least three sets of branches appear.
During the growing season, dahlias produce many flowers, which will help create a fuller plant.
Dahlias need deadheading after blooms fade to help encourage new growth.
Use a sharp tool to make clean cuts, or use your fingers.
However, you could allow up to 10 flowers if you want smaller flowers.
Propagating Dahlias
The most common methods to propagate dahlias include cuttings and dividing tubers.
Inside the old blooms, seed pods are available around one month before the first frost.
Additionally, dahlias seeds are available at garden stores for purchase.
Dahlias grown from seed may turn out to have smaller, simpler, and fewer blooms.
Grow dahlias by seed using a seed-starting tray filled with seed-starting mix.
Start planting seeds in late winter or around two months before the final frost.
After a few sets of leaves form, dahlias can move to containers and be fertilized at 1/2 strength.
Slowly harden off the plants during daytime before transplanting.
Choose a plastic container with drainage holes.
Fill about half way with light, well-draining potting mix.
Water once and then wait for sprouts to appear before beginning regular watering.
Dahlia plants can also be potted using a container that is slightly wider than the nursery pot.
Plant these at the same depth in well-draining, organically rich potting mix and keep lightly moist.
Use garden stakes, driven to the bottom of the container, to help tall plants stay upright.
Cut branches to around 6 inches and gently remove tubers from the ground.
scrub the tubers of rotten roots using a clean, sharp knife.
Occasionally, spray tubers with water throughout their dormancy and use compost to help them from completely drying out.
Once the final frost passes, you could move the tubers back outside.
Common Pests & Plant Diseases
Dahlias are relatively susceptible to pests.
Slugs are most destructive to dahlias during the early growing season because the leaves are more tender.
Dry soil helps prevent slugs from attacking healthy leaves.
Some diseases that impact dahlias include stem rot,Botrytisblight, and powdery mildew.
Maintaining the correct amount of water and balancing soil and sunlight helps prevent these diseases from forming.
Additionally, since some dahlias grow very tall, using garden stakes will help them to stay upright.
Finally, remember to deadhead wilted or faded blooms so they don’t take away nutrients from healthy flowers.
Leafhoppers spreadaster yellows, a disease that can deform both foliage and flowers.
Leaves on the plant may turn yellow.
There is no way to cure this disease.
Remove and discard any dahlias and surrounding plants and weeds that appear infected.
You must remove all plant parts, including tubers, to prevent aster yellows from persisting in the garden.
Remove diseased branches with a sharp pruning tool.
Frequently Asked Questions
Potting dahlias provides several advantages over growing them in the ground.
However, container-grown dahlias require more watering and fertilizing.
Dahlias can overwinter in the soil in USDA Plant Hardiness Zones 8-10 and return in spring.
But wet soil, rodents, or insect pests could potentially destroy the tubers over winter.
In frost-free climates like Florida, dahlias may be planted in late fall instead.
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