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Growing Dahlias
How to Plant, Grow, and Care for Dahlias
How to Plant, Grow, and Care for Dahlias
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2019 is the Year of the Dahlia! These colorful, spiky, daisy-like flowers bloom from midsummer right through first frost, when many other plants are past their best. Plant bulbs in the springtime and prepare to be wowed! Learn more about dahlias, growing tips, and new varieties.
The National Garden Bureau has selected the beautiful dahlia as the bulb of the year.
Dahlia is a genus of tuberous plants that are members of the Asteraceae family; related species include the sunflower, daisy, chrysanthemum, and zinnia. They grow from small, brown, biennial tubers planted in the spring.
Picking a favorite dahlia is like going through a button box. As well as coming in a rainbow of colors, dahlia flowers can range in size from petite 2-inch lollipop-style pompoms to giant 15-inch “dinner plate” blooms. Most varieties grow 4 to 5 feet tall.
They are considered a tender perennial in cold regions North America. They are only winter hardy in planting zones 8 to 11. Gardeners in zones 2 to 7 can simply plant dahlia tubers in the spring and either treat them as annuals or dig them up and store for winter.
Dahlias love moist, moderate climates. Though not well suited to extremely hot climates (southern Florida or Texas), dahlias brighten up any sunny garden with a growing season that’s at least 120 days long.
Planting
When to Plant Dahlias
- Don’t be in a hurry to plant; dahlias will struggle in cold soil. Ground temperature should reach 60°F. Wait until all danger of spring frost is past before planting. (We plant them a little after the tomato plants go in.)
- Some gardeners start tubers indoors in containers a month ahead to get a jump on the season. Medium to dwarf-size dahlias will do well in containers.
Choosing and Preparing a Planting Site
- Select a planting site with full sun. Dahlias grow more blooms with 6 to 8 hours of direct sunlight. They love the morning sunlight best. Choose a location with a bit of protection from the wind.
- Dahlias thrive in rich, well-drained soil. The pH level of your soil should be 6.5-7.0, slightly acidic.
- If you have a heavier (clay) soil, add in sand, peat moss, or aged manure to lighten and loosen the soil texture for better drainage.
- Large dahlias and those grown solely for cut flowers are best grown in a dedicated plot in rows on their own, free from competition from other plants. Dahlias of medium to low height mix well with other summer flowers. If you only have a vegetable garden, it’s the perfect place to put a row of dahlias for cutting (and something to look at while you’re weeding!).
How to Plant Dahlias
- Avoid dahlia tubers that appear wrinkled or rotten. Pink “eyes” (buds) or a little bit of green growth are good signs. Don’t break or cut individual dahlia tubers as you would potatoes.
- Bedding dahlias can be planted 9 to 12 inches apart. The smaller flowering types, which are usually about 3 feet tall, should be spaced 2 feet apart. The taller, larger-flowered dahlias should be spaced 3 feet apart. If you plant dahlias about 1 foot apart, they make a nice flowering hedge and will support each other.
- The planting hole should be slightly larger than the root ball of the plant and incorporate some compost or sphagnum peat moss into the soil. It also helps to mix a handful of bonemeal into the planting hole. Otherwise, do not fertilize at planting.
- Dig a hole that’s about 6 to 8 inches deep. Set the tubers into it, with the growing points, or “eyes,” facing up, and cover with 2 to 3 inches of soil (some say 1 inch is adequate). As the stem sprouts, fill in with soil until it is at ground level.
- Tall, large-flowered cultivars will require support. Place stakes (five to six feet tall) around plants at planting time and tie stems to them as the plants grow.
- Dahlias start blooming about 8 weeks after planting, starting in mid-July.
- Do not water the tubers right after planting; this encourages rot. Wait until the sprouts have appeared above the soil to water.
- Do not bother mulching the plants. The mulch harbors slugs and dahlias like the sun on their roots.
Care
How to Grow Dahlias
Watering
- There’s no need to water the soil until the dahlia plants appear; in fact, overwatering can cause tubers to rot. After dahlias are established, provide a deep watering 2 to 3 times a week for at least 30 minutes with a sprinkler (and more in dry, hot climates).
- Like many large-flower hybrid plants, the big dahlias may need extra attention before or after rain, when open blooms tend to fill up with water or take a beating from the wind.
Fertilizing
- Dahlias benefit from a low-nitrogen liquid fertilizer (similar to what you would use for vegetables) such as a 5-10-10 or 10-20-20. Fertilize after sprouting and then every 3 to 4 weeks from mid-summer until early Autumn. Do NOT overfertilize, especially with nitrogen, or you risk small/no blooms, weak tubers, or rot.
Pinching, Disbudding, and Staking
- When plants are about 1 foot tall, pinch out 3-4 inches of the growing center branch to encourage bushier plants and to increase stem count and stem length.
- If you want to grow large flowers try disbudding—removing the 2 smaller buds next to the central one in the flower cluster. This allows the plant to put all of its energy into fewer but considerably larger flowers.
- Bedding dahlias need no staking or disbudding; simply pinch out the growing point to encourage bushiness, and deadhead as the flowers fade. Pinch the center shoot just above the third set of leaves.
- For the taller dahlias, insert stakes at planting time. Moderately pinch, disbranch, and disbud, and deadhead to produce a showy display for 3 months or more.
Winter Care
- Dahlia foliage blackens with the first frost.
- Dahlias are hardy to Zone 8 and can be cut back and left in the ground to overwinter; cover with a deep, dry mulch. Further north, the tuberous roots should be lifted and stored during the winter. (Some readers find, however, that dahlias will survive in Zone 7 if the winter isn’t too severe.)
- See Harvest/Storage (below) for more information.
Pests/Diseases
- Slugs and snails: Bait 2 weeks after planting and continue to bait throughout the season.
- Mites: To avoid spider mites, spray beginning in late July and continue to spray through September. Speak to your garden center about recommended sprays for your area.
- Earwigs and Cucumber Beetle: They can eat the petals though they do not hurt the plant itself.
- Aphids
- Deer: Find a list of deer-resistant plants to grow around your dahlias.
- Powdery Mildew: This commonly shows up in the fall. You can preventatively spray before this issue arises from late July to August.
Harvest/Storage
Dahlia Bouquets
Dahlias are beautiful in a vase. Plus, the more you cut them the more they will bloom.
To gather flowers for a bouquet, cut the stems in the morning before the heat of the day and put them into a bucket with cool water. Remove bottom leaves from the stems and place the dahlias in a vase. Put the vase in a cool spot and check the water daily. The bouquet should last about a week.
Taking Up the Tubers
In cold regions, if you wish to save your plants, you have to dig up the tubers in early fall tubers after the first frost in the fall and store them over the winter.
Dahlias may be hardy to USDA Zone 8. There, they can be left in the ground to overwinter. In areas that get frost, including most parts of Zone 5, a killing frost—or a touch of frost—can help the bulb to shut down/go dormant. See your local frost dates.
- After fall frost has blackened the foliage, cut off all but 2 to 4 inches of top growth
- Carefully dig tubers without damaging them.
- Lift and gently shake the soil off the tubers.
- Cut rotten tubers off the clump and leave the clumps outside in the sun upside down to dry naturally.
- Pack in a loose, fluffy material (vermiculite, dry sand, Styrofoam peanuts).
- Store in a well-ventilated, frost-free place—40 to 45º F is ideal, 35 to 50º F is acceptable.
- Take out the tubers in the spring, separate healthy tubers from the parent clump, and plant in the garden. Each tuber must have at least one “eye” or a piece of the crown attached or it will not develop into a blooming plant. The eyes are located at the base of the stem and look like little pink bumps.
- If this all seems like too much bother or you do not have the right storage place, skip digging and storing, and just start over by buying new tubers in the spring.
Recommended Varieties
There are about 60,000 named varieties and 18 official flower forms including cactus, peony, anemone, stellar, collarette, and waterlily. The American Dahlia Society recognizes 15 different colors and color combinations. Here are some popular choices:
- ‘Bishop of Llandaff’: small, scarlet, intense flowers with handsome, dark-burgundy foliage
- ‘Miss Rose Fletcher’: an elegant, spiky, pink cactus plant with 6-inch globes of long, quilled, shell-pink petals
- ‘Bonne Esperance’, aka ‘Good Hope’: a foot-tall dwarf that bears 1-½-inch, rosy-pink flowers all summer that are reminiscent of Victorian bedding dahlias (though it debuted in 1948)
- ‘Kidd’s Climax’: the ultimate in irrational beauty with 10-inch “dinnerplate” flowers with hundreds of pink petals suffused with gold
- ‘Jersey’s Beauty’: a 7-foot tall pink plant with hand-size flowers that brings great energy to the fall garden.
Image: Kidd’s Climax. Longwood Gardens
Wit & Wisdom
- The dahlia was named for Anders Dahl (Swedish botanist), born on March 17, 1751.
- In the 16th century, dahlias grew wild on the hillsides in parts of Mexico. There, they were “discovered” by the Spanish, who remarked on the plant’s beauty.
- Both dahlia flowers and tubers are edible. The tubers taste like a cross between a potato and a radish.
The Dahlia you brought to our isle
Your praises forever shall speak
‘Mid gardens as sweet as your smile
And colour as bright as your cheek.
–Lord Holland (1773–1840)
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Reader Comments
Leave a Comment
Height of Dahlias
Hi I've had my beautiful Dahlias about 3 years now. I leave them in the bed in the winter and they're as thick as a forearm now!! My issue is I'd like the bed to be a cushion of flower heads at about 3 foot. Last year most of them grew to 5/6 foot so there was just a wall of green next to the patio. They're tall varieties but is there any way to keep them shorter but still full of flowers??
Thanks
Dahlias
I've been completely in love with Dahlias ever since my husband got me some for our Thanksgiving centerpiece, and now I want to add them to my garden. It's really good to know they don't do well in cold soil; I'll definitely wait until later spring before planting any. Checking the soil pH is a good idea, as well, because I really want these to thrive, so I'll be sure to look into that.
lifting Dahlias early before frost
It's November and I have not had a hard frost. Can I lift the Dahlias and store for next winter before a frost?
I live in zone 7, outside Washington DC
Accidentally pulled bulbs while planing in pot
Hi!
I just bought a Dahlia and when I went to transfer the plant to a pot the bottom of the soil got stuck and the bulbs were disconnected from the plant. Will this kill the plant?
re plant a fully grown plant
I noticed one of my dahlia plants is not growing very tall, i think because the water is not getting to it, i would like to uproot the plant and put in a large pot. thoughts please....
replanting the dahlia
I bought a dahlia a large one with big flower do I need to re pot the plant, the flowers are hanging down
Dahlias not producing buds
I have 3 Dahlia plants. Only one is producing buds and flowers. All three were planted at the same time. The other 2 plants looks healthy, but no buds or flowers. What's up with this?
Dahlias
Is it recommended to cut down the first shoots to encourage more shoots to grow,Ihavebrought the tubers on prior to planting out.
Pinching Dahlias
If you haven’t planted the tubers yet, then yes, you should trim the shoots down to 1 inch before planting. It’s recommended to pinch back stems only slightly once they have developed 3 to 4 sets of leaves. This will encourage the plant to branch out from the stems, giving you a fuller plant.
Potted Dahlias
What is the care for potted dahlias?
dahlias in pots
Growing in a pot/container is essentially the same as in the ground. Make sure that the pot is large enough to give the tubers room to spread out, and if staking/support is needed, arrange it in the pot when you plant the tuber (as if you were planting in the ground). Staking later risks injury to the tuber and potentially loss of it or the bloom.
Growing in pots
Can l over winter dahlias in pots in a garage or greenhouse l live in the uk
Dahlias in pots??
I live inOlive Branch ,Mississippi. ( right by Memphis Tennessee ). Can I grow Dinner plate Dalias in Large pots?( I’ve already planted & they are starting to come up....3 inches tall) my pots sre 24 inched wiwide & 3ft tall.
Dahlias
I planted 6 tubers and now I have 30 plants. What do I do?
from 6 plants to 30
It’s not entirely clear: If you now have 30 plants in the ground, you can lift the tubers and divide them. This is best done in spring or fall. Use a sharp knife to cut the tubers apart. Note that only those with an eye (a dormant bud) will grow stems, so you can cut large clumps of tubers instead of discarding single ones without eyes. Let the roots dry for a day or so before storing (see above) or planting elsewhere.
confused about planting depth
Hi, I'm confused. The article says: "Plant them whole, with the growing points, or 'eyes,' facing up, about 6 to 8 inches deep. The crowns should be just above soil level."
How can they be 6-8" deep but still be at soil level??
Thanks!
confused about soil cover
Thank you for pointing out the error in the text. We have corrected it. Here’s what we learned: you want to dig a hole that’s 6 to 8 inches deep. Set the tubers into it and cover them with 2 to 3 inches of soil (some say 1 inch of soil is ok, too). As the plant grows/sprouts up, fill in with soil around it until the ground is level. BTW, if you plan to stake the dahlia, place the stake in the hole first, then the tuber and cover as described. If you wait to push a stake into the ground, you might strike and damage the tuber. Thanks again!
Dahlias
I started dahlia seeds one day and saw the seeds already laying on top of the mix already is that normal I poked the seeds back down in the mix. Thank you, Lisa.
Dahila
I put my Dahila away for the winter (MN), it is in the basement so cool and dry. I have discovered that it is growing. It is about 8-12 in in growth and very spindly. Is there anything I can do stop the growth? Can / should I cut it back ?
Thanks for any help. ( I'm a first time owner)
dahlias that sprout in storage
The general consensus is not to break off the shoots and plant the dahlia tuber as you would normally. If there is any rot, cut it off, and be aware that if the tubers are dried out, they may not thrive or grow. A reader wrote in to endorse the idea of leaving the tubers as is: “I never break them off [when] they grow new shoots, [and] never have a problem with them growing.”
2 Dahlia plants, 1 flowering, the other not
Hi, I have 2 pots of Dahlia, one is flowering nice but the other is just growing bushy with tiny buds which do not open. How do I treat it?
Thank you from Ghana.
tiny buds, do not open
I have potted plants that look healthy and have buds but do not open.
Dahlias
What if some tubers fall off when pulling out? Are they still good?
Rotten Tubers
If your dahlia tubers fall apart when being lifted out of the ground, then they are rotten and should be disposed of. If it’s just the foliage that detaches from the tubers, the tubers themselves are probably just fine; you’ll have to dig them up and have a closer look. If they are squishy and fall apart easily, then they are no good. In the fall, especially after a frost, the foliage dies off naturally, which is when it easily detaches from the tuber.
dahlia
I live in the Seattle area, did not replant my very dark purple dahlia for 5 yrs, this year the plant bloom in a yellow and orange color, WHY?
Thank you, Renee
Color-Changing Dahlia
Some cultivars of dahlias (and other common-grown flowers) are not genetically “stable,” meaning the flowers they send up may not always be the same color or shape. Your original purple dahlia was likely a hybrid of several other dahlias, and it just so happens that another color showed up this time.
Colour changing Dahlias
I live in England and have experienced this with blue hydrangeas that turned pink. I researched and learnt that at transplanting, the acidity of the soil has a bearing on the flower colour. Solution is to buy erocutious compost. I use this for camelias as well
dahlia
For the last two years I have grown the most abundant and beautiful dahlia. They had very large blooms. However after I dug them up in the fall and stored them over winter they did not grow. This year I bought new tubers and they grew tall but the flowers did not fully bloom they were undeveloped and looked sick. It was very dry here so I watered them but they were slow to come up and the blooms would not develop
Weak Dahlias
There are a couple things that could have resulted in weak dahlias:
1. The tubers themselves could have come from a bad or diseased source.
2. There aren’t enough nutrients in the soil. Did you add any fertilizer to the soil before planting? Dahlias are heavy feeders, so having two seasons of dahlias grow in the same spot without any extra fertilizer could have simply depleted the soil’s resources. See our advice, above, about fertilizing dahlias.
dahlias falling over
my dahlias did spectacularly well in a large pot from late spring until mid august, I did not stake them. now they have fallen over. how far back can I prune them. also the tuber is about half above ground. should I bury it?
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