How to Care for Dahlias

Co-authored by Andi Xoch

Last Updated: January 20, 2023 References Approved

Dahlias are tubers that are native to the mountains of Mexico, Central America, and Colombia. They do best in cool, humid climates with long summer growing seasons. Take care to water, cut and winter your dahlias, since they are more sensitive than many garden flowers.

Part 1

Part 1 of 3:

Planting Dahlias

1
Ensure you have a growing season of at least 120 days. You can’t plant dahlias until the soil in your garden is over 60 degrees Fahrenheit (16 Celsius), so planting can occur between April and June, depending upon your location. You can usually plant these tubers around the same time as you plant your tomatoes.
- These tubers prefer morning sunlight, and they can benefit from shade in the hottest hours of the afternoon.
- Check your hardiness zone at http://planthardiness.ars.usda.gov
- Dahlias do best in zones 8, 9 and 10, where they do not need to be dug up every winter. They do best in the Pacific Northwest of the United States. Dahlias can also be planted in colder zones with long, sunny summers.
2
Buy dahlia tubers that are not browning too much. You must cut off any rot you see before planting.^{[1]
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- If you want to combine them with other flowers in your flower beds, it is recommended that you choose small to medium varieties so they don’t compete too much with other plants.
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3
Store them in sand or packing peanuts until you are ready to plant them.^{[2]
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4
Enhance your garden soil with loamy soil, such as peat moss or sand. They also like slightly acidic soil with a pH of 6.5 to 7. Ensure you are amending the soil in a well-drained portion of your garden.^{[3]
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- Avoid using packaged topsoil that has been pre-treated for weeds.^{[4]
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5
Dig into the soil approximately 6 to 8 inches (15 to 20 cm) to plant dahlia tubers. Dahlias with large blooms should be spaced 18 to 24 inches (46 to 61 cm) apart in rows. Place a sprinkling of bone meal in the hole for a preliminary fertilizer.^{[5]
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- Smaller, bedding dahlias can be planted closer, approximately 9 to 12 inches (23 to 30 cm) apart.
6
Make sure the eyes of the tubers are facing toward the sky. Cover them with soil. Mound them with 6 inches (15 cm) of soil. ^{[6]
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7
Don’t water the plants until you start to see them sprout. They will rot easily in overwatered soil.
- If you live in a very dry climate, you can moisten the soil slightly before planting.
8
Set a sprinkler to water your dahlias after they are established. These plants require a great deal of water. They should be watered for 30 minutes at a time 2 to 3 times per week. Make sure the water is gentle and drains completely.^{[7]
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- The water must reach a depth of at least 4 inches (10 cm).
- Some warmer, drier climates may require watering every other day.
9
Bait your garden for slugs and snails immediately after planting. Slugs particularly love small, immature dahlias.^{[8]
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10
Stake your dahlia plants at the time of planting, if they are large blooms. They will need the support later in the growing season. As they grow, you can tie the stems to the stakes with nylon hose or garden tape.

Part 2

Part 2 of 3:

Caring for Dahlias

1
Fertilize with a low-nitrogen fertilizer once per month, once the dahlias are 2 to 4 inches (5 to 10 cm) tall. Avoid over-fertilizing, since dahlias can be sensitive to this.^{[9]
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- Avoid fertilizing late in the season.
2
Find and pinch the terminal bud when the plant is 3 to 4 inches (7.4 to 10 cm) tall. This is the point below the second set of leaves. It will cause the plant to divide and create more blooms.^{[10]
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3
Cut dahlia flowers at the base of the stem when they are in full bloom. Wait until the stem is at least the length of your wrist to your elbow. Blooms come in groups of 3, and you can pinch off the left and right blooms to produce a larger central bloom.^{[11]
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- Place the cut flowers in hot water. Then, let them cool over the next hour. They should last 4 to 6 days.
- Cut your flowers in the morning for best results.
4
Deadhead spent blooms and cut flowers regularly through the season to encourage a fuller plant with more blooms.
5
Keep an eye out for aphids and spider mites. You can spray the plants with insecticidal soap to discourage pests.

Part 3

Part 3 of 3:

Wintering Dahlias

1
Wait until after the first frost to remove dahlia tubers. The foliage will begin to blacken when it gets cold. Wait several days after that, so that the tubers can freeze.^{[12]
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2
Cut dahlia stalks at 6 inches (15 cm) from the ground and mulch them in zones 7, 8 and 9. Make sure you have a thick layer of mulch to insulate them over the winter.
- Dig up tubers in colder climates.
3
Dig up the tubers with a spade, if you are going to store them inside for the winter. This is necessary to avoid killing them in all cold winter climates.
4
Cut off the stalk at 6 inches (15 cm) from the base. It's also a good idea to cut dahlia tubers so that each individual tuber is separated from the clump. Rinse the dahlias to remove soil and allow them to air dry.
5
Line a cardboard box with newspapers. Set the dahlia tubers in the box so that they are not touching. Pour sand, peat moss or packing peanuts around the tubers.
6
Store in a cool, dry climate between 40 and 50 degrees Fahrenheit (4 to 10 Celsius).^{[13]
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Community Q&A

Question

I just bought dahlia bulbs, and I think it is too late to plant them. Will the bulbs last until next year, and should I store them in the refrigerator?

Community Answer

Dahlias are a tuber, and as such, are like a potato in storage. You can put them in peat moss and then into a box or a paper bag, and keep cool, but not cold. Do not allow to freeze. Keep in the dark, as light will cause them to sprout. In April, bring them out and divide the tuber with a sharp knife. At that point, you can either plant in pots for an early start, or outside, depending on your climate. The big tubers are better keepers than the tiny ones.
Question

Can dahlias grow indoors inside a container?

Community Answer

It is possible, given that you have the right conditions. Dahlias need plenty of sun to flower well, so a south or east-facing window may be ideal. However, make sure to avoid harsh afternoon sun. Use a big enough pot so that your dahlia can form big roots.
Question

My dahlia leaves are yellow along the edges. What should I do for them?

Community Answer

One thing you could do is get a liquid nitrogen as a foliage feed. They have a low nitrogen but when the leaves start to turn like a pale yellow ike you described, putting some nitrogen fertizler would really help the plant.