Dahlias have become one of the most popular flowers in the world! They are incredibly popular on social media and for wedding arrangements. They are a flower that incites frenzies and causes long lines to appear at flower farm shops in the spring when tubers go on sale. Online sellers post their available varieties ahead of store opening and can sell out in a matter of hours. A single tuber can cost upwards of $12!
Once you’ve grown them, though, and admired the perfect symmetry of a bloom in that golden hour of waning sunlight, you may find yourself hooked. Bitten by the dahlia bug. Welcome to the club.
Dahlias bloom from midsummer until a hard frost (mid to late October). There is a rainbow of colors available – whites and creams, yellows and oranges, pinks and reds, raspberry and lavender, even multicolored blooms.
The blossoms range in shape and size – from an inch or two in diameter to the size of a dinner plate. Some flowers have a single rim of petals around a fuzzy center, while others form a complete ball of petals. The petals themselves may be curled up or flattened out, and may have smooth tips, pointed tips, or fringed tips. They can even be “lacinated” – slightly twisted and split.
Growing Dahlias
So, what does it take to grow them?
First, select a sunny spot with soil that drains well. Dahlias grow best with at least six hours of sun. They appreciate consistent water, but, if the soil stays saturated too long, they can rot and your efforts will be lost!
You can grow from seeds or from tubers.
When you collect seeds from a dahlia, the plant you get can vary widely from the parent plant. This is how new varieties are developed. A tuber is the root portion of a dahlia and looks a lot like a potato. It has all of the same DNA as the parent plant, so it will give you a clone.
As a dahlia grows, each one will produce multiple tubers. Like the flowers, the tubers can vary widely in size and shape, too. Some are pencil thin, some really look like small potatoes, and others can be as large as your hand. Some plants produce a few tubers, some produce a huge cluster!
Different varieties reach different sizes. Some are tiny and great for containers, not reaching much more than a foot tall. Others will grow so tall and broad that blooms may be at head height!
Planting
Planting a dahlia is pretty easy to do. You can plant a single tuber or a clump. Once the soil is warm (at least 50°), it is possible to plant. The tubers will need warm soil, but will have more success after the heavy rains of spring have passed.
When deciding where to plant, a spacing of about 18″ apart is pretty good for most larger varieties. They should be planted with the tubers laying sideways, about 4-6″ below the surface. This year, I prepped the soil by mixing in a sprinkling of bone meal and an inch or two of compost (suggestions from some of the large dahlia farmers).
Supporting
Many dahlias grow to be bushy and about 4′ tall, with even larger plants possible. Tall stems and large blooms can make them top-heavy and require support.
There are many ways to help keep your plants upright and prevent them bending or snapping in the wind. If planting just a few, try using stakes — like bamboo canes or coated metal — that you can tie stems to as they grow. Some gardeners also use tomato cages for support. If you’re planting a lot in one area, you may want to use netting or a criss-cross bracing method. This year I tried two layers of horticultural netting with a 6″ grid, held tight by bamboo stakes, and the dahlias have grown right up through it. Others place stakes along the outside of the bed and use sturdy twine to form an X pattern between them, and also around the perimeter. Whichever option you choose, try to get it in place early in the season. Your dahlias won’t flop over, and their foliage will grow to disguise the supports.
Feeding
Dahlias grow quickly and do well in nutrient-rich soil. However, the balance of nutrients is important to encourage flowering. If you are fertilizing your plants, be aware that high nitrogen levels (the first number on fertilizer packaging) encourage lots of leafy growth, but few flowers. A fertilizer with a higher phosphate (the middle number) can help to stimulate flower growth. Many all purpose garden fertilizers and tomato fertilizers have a balance that would support flowering, like 5-10-5.
Cutting
Dahlias look beautiful in the late summer and fall garden, but they’re also great as cut flowers. Like many of our garden plants, they will keep producing more blooms after you’ve cut some.
When choosing which flowers to cut for an arrangement, try to select those that are not quite fully open and cut the full stem. Once the centers are open and the pollen is visible, the bees and butterflies will be doing what they do. Once pollinated, a flower’s job is “done” and it may fade quickly as the energy shifts to seed production. Try to select flowers where the petals on the back still look “fresh”. As the bloom ages, the petals on the back start to turn brown. The flowers don’t last as long if you cut them at this stage.
It’s best to avoid the heat of midday and cut in the early morning or evening, placing stems right into water. Some growers will use flower food or treat their stems (there are hot water methods and chemical methods), but I’ve found that cut dahlias will last for about a week with no special treatment. For best vase life, make sure they are in a cooler spot, out of direct sun, with clean water.
To keep your dahlias flowering as much as possible, be sure to deadhead spent flowers, removing the full stem for that flower. Once the petals drop, it can be tricky to tell the difference between a new bud and that left behind after a flower. New buds will be rounder and firm, while the spent ones will be more cone-shaped, will feel soft if given a gentle squeeze, and may even be a bit wet.
As the Season Ends
Dahlias will bloom from summer into fall, but they are frost sensitive. They will continue to be vibrant and full of flowers right until a hard frost comes (around mid-late October for me). When it does, it will kill the foliage and flowers and the plants will turn nearly black. To make sure you know which plants are which when this happens, be sure to tag them while they’re still blooming! I often mark plants with popsicle sticks in the spring that, of course, decompose during the season. This fall, I’m going to use plastic nursery-style tags at the base of each plant so I remember who’s who at frost time.
Once the frost comes, you can cut the plant back completely. I leave maybe 6″ above the ground so I know where they all are, and to serve as a handle as I lift them all. Once your foliage is all removed, you can dig up the tubers! They key when digging up the tuber clumps is to be gentle, and assume they’ve grown quite a bit. A gardening fork is pretty safe to dig with, but you can use a shovel if you’re careful. I start about 12-18″ from where the stems are, and work in and under, gently prying them up. Once you know where the clump is, you can dig a bit more confidently. Lift the clump up, check the hole for any tubers that may have fallen off, and you’ve done it! Before tossing them all in a box together, make sure they’ve got some kind of tag on them so you can keep them straight.
When you’ve dug up all of the tubers, give them a rinse to remove as much dirt as you can, then let them dry off for about 24 hours. Now they’re ready to be divided (if you’d like) and stored.
Dividing
Many gardeners divide their dahlias to have more individual plants the following season. After following many flower farmer social media accounts, this seems to be much more common here in the US than it is in the UK.
Dividing can be done in fall or spring. You can make small clumps or separate individual tubers. Sometimes you’ll find that what looks like one large clump is a few smaller clumps tangled together. I follow the stems down and look to see what they’re connected to. A little bit of gentle coaxing to unweave the ‘potatoes’ can easily result in multiple clumps.
If you divide, there are some things to know about a tuber. The most important– it has parts! Each tuber must have a body, a neck, and a crown (fitting for the “queen of cut flowers”). The crown is the portion nearest the stem that contains the information the tuber needs to grow. If a tuber has no crown, or a broken neck, it may sprout roots, but it will not grow into a plant.
Storing
This can feel a bit intimidating. How do you know where to keep that precious tuber? Too warm and it may try to sprout. Too cold and it could freeze (and become mush upon thawing). Too moist and it could get moldy. Too dry and it could shrivel up. Very Goldilocks…
Think about how you might store a potato or other root vegetable. They want to be cool, mostly dry, and dark. I store mine in an area of my basement that’s a bit like a root cellar. It’s dry, but breathes a little because it has a brick floor. It stays cooler because it’s away from the heat and has makeshift cabinets to create some separation.
one in fall or spring. You can make small clumps or separate individual tubers. Sometimes you’ll find that what looks like one large clump is a few smaller clumps tangled together. I follow the stems down and look to see what they’re connected to. A little bit of gentle coaxing to unweave the ‘potatoes’ can easily result in multiple clumps.
If you divide, there are some things to know about a tuber. The most important– it has parts! Each tuber must have a body, a neck, and a crown (fitting for the “queen of cut flowers”). The crown is the portion nearest the stem that contains the information the tuber needs to grow. If a tuber has no crown, or a broken neck, it may sprout roots, but it will not grow into a plant.
Some gardeners store tubers in peat, some in lightly moistened sand, some in dry seed planting mix, and some in mulch. I’ve even stored them in cardboard boxes lined with shipping paper that I loosely folded over them. Plastic totes are super handy for storage, especially shoebox size. You can get them at the dollar store, as well as labels; they’re stackable; and they’re an easy size to handle.
After you decide what might work best for you, check on them once in a while. Every few weeks, peek into a few containers to make sure the tubers aren’t drying out too much and looking shriveled (give them a light sprinkle if they’re dry), and that you don’t see condensation inside (pop the lid for a day or two if you do).
As winter starts to turn to spring and temperatures start to warm up a bit, you might see sprouts from some of the tubers. Don’t panic that you have to get them in the ground right away! In storage, these sprouts will likely grow very slowly. It’s completely fine to have a tuber with small sprouts on it and to bury the entire thing at planting time.
In early spring, you can plan your next dahlia garden! To try to get a headstart on the season for the earliest blooms, you can put tubers into pots indoors. If you do this with your dahlias, only give them a very light watering until you see growth above the soil so that they don’t rot. Similar to starting seeds, they can be transitioned outside once the soil warms.
When the weather warms, the dahlia cycle begins again and we anxiously await the late summer show!
Resources
There are many places to find information on dahlia growing, or to discover new varieties.
Here are just a few of the accounts I’ve found on social media, along with a few books to consider.
Floret Flowers – Erin Benzakein is a farmer-florist who is dedicated to getting more flowers growing in the world. She no longer sells dahlias, but has inspired many and continues to via instagram, @floretflower. She has a few books on cut flowers including on just on dahlias: Floret Farm’s Discovering Dahlias: A Guide to Growing and Arranging Magnificent Blooms www.floretflowers.com/
Santa Cruz Dahlias – Kristine Albrecht. Located in California, Kristine has short videos on dahlias and has written a book on breeding them! She pollinates her own, saves seed, and works to create new varieties. @santacruzdahlias www.santacruzdahlias.com
Book: Dahlia Breeding for the Farmer Florist and Home Gardener
Swan Island Dahlias – They sell tubers via their website, www.dahlias.com, and have a great instagram page, @swanislanddahlias. In addition to lots of dahlia photos there is a series of “Dahlias 101” videos, covering planting, feeding, digging, washing, dividing — all of it!
Triple Wren Farms – Pure eye candy. This family-run flower farm and florist grows thousands of dahlias in Washington state. Their instagram account, @triplewrenfarms does a really nice job of showing the differences between varieties, with labeled photos! www.triplewrenfarms.com
