How to Grow Perfect Dahlias
Dahlias are the quintessential flower. Whether growing in the garden, cut for a vase on the table, or in a flower farmer’s fields to be used in weddings, bouquets and installations, they are quite possibly the most popular and more demanded flower these days.
It used to be that dahlias were relegated to enthusiastic hobbyists, who would carefully pamper and debud their plants for exhibition in the fall. Although impressive, they were only seen as specimen plants to be exhibited at garden centers and for a select intellectual few.
Something changed though. Perhaps it was Martha Stewart (the original flower queen) and her love of dahlias in the garden that led to their re-discovery. Perhaps it was garden enthusiasts like Sarah Raven that reinvigorated the use of dahlias in the garden as not just straight single-flower specimens grown for competitions, but rather for enjoyment and cutting for the vase. Or maybe it was Erin Benzakein of Floret Flower Farm with her photographs of armloads of dreamy dahlias in the Skagit Valley sunset that made the world fall in love with them.
Regardless, dahlias are definitely here to stay. Whether ball, pompon, waterlily, dinnerplate, informal decorative or cactus, dahlias are loved by gardener, flower farmer, floral designer and flower loves alike. There are few people who don’t like dahlias, and I feel bad for those who do.
Maybe it’s because of their perfect radial symmetry that draws us in. Or the hundreds of color combinations with their playful names like “Ginger Willo” and “Hamari Gold” and “Chickadee” or “Winie the Pooh” that provides something for everyone to love. Or the fact that they are easy to grow and will crank out armloads of blooms all season long, right up until frost. Or the fact that they are unrivaled as far as their role in floral design, and are especially unique since they are so hard to come by.
Yet, just looking at a perfectly formed “Cafe au Lait” dahlia, there’s something more. Something just romantic and alluring - like many layers of ruffled silk petticoats or tutus that make it’s appearance immediately delicate, elegant, and beautiful in a way that words cannot describe.
Regardless of the reason why you want to grow dahlias, they’re not difficult to grow so long as you know a few things about them.
1. Choosing your Variety
Dahlias are not all created equal - there are a great variety of dahlias out there, and it’s hard to know the best ones for cut flowers if you haven’t grown them before.
Generally speaking, there are two broad categories
Bedding dahlias are short and stocky. They produce beautiful flowers - usually a collarette or ball type - but have little to no stem to speak of. They have appropriate names- Itsy Bitsy, Baby, Dwarf - and will grow to only about 12” or so. Great for planters and for the front of the border, but not great for cutting.
Exhibition dahlias are pretty much every other variety out there. 24” is a useable stem, but some dahlias can get up to 48” on average - and if grown in the right environments can get even up to 60”-72” inches! These are the types that you’d want to grow if you want to use them as a cut flower.
While there are a few dahlias grown from seed that get tall enough to cut - the Double Pompon and Cactus Flowered Hybrids, Showpiece Double Mixed and Bishop’s Children - generally speaking they are a mixed bag of blooms, with a lot of the blooms being rather pathetic, mutated single blooms that don’t even make it to the vase.
To get the perfect, amazing, dreamy dahlias, it’s important to purchase tubers - the roots of the dahlia plant that you can put in the ground and grow a giant bush of a plant in just one season.
Tubers should be purchased in spring and planted out when it starts getting warm. We’re technically supposed to plant out after the last frost date, but we usually plant a little bit earlier - simply because we get a lot of sun and in our dry climate the ground heats up quickly, which gives us a headstart on the growing season. If you live in a cooler area that gets a lot of spring precipitation like the PNW or the upper Midwest you may want to hold off on planting until the ground dries out and gets a bit warmer.
If you’re really interested in getting a big headstart, you can also start tubers in pots well ahead of the frost date. If you have a greenhouse, they will fit perfectly into there so long as it stays above freezing - or even a basement or heated garage will allow for you to start tubers early.
Just know that the earlier that you get dahlia tubers some heat and light, the sooner you’ll have blooms. For us, we start getting early blooms around the end of June, early July. And once they start, they don’t stop blooming!
3. Planting Out
When planting out tubers, you should plant them so that the eye of the tuber (where the beginning buds of the plant are starting to sprout) is facing upwards. We tend to only plant the top of the eye a couple inches below the ground - enough to anchor the stem into the ground, but not too far so that the eye struggles to reach the surface.
Since we grow our dahlias quite close together (so we can avoid staking each individually and instead have them support each other) we plant ours 6” together. Sacreligious I know, but we live in such a dry environment that any issues with powdery mildew or fungal diseases are kept to a minimum, allowing us to grow lots of dahlias in a very small amount of space.
If you live in an area which is more humid than our part of the world (which is pretty much all other places in the US) then you’ll want to space yours out to at least 12”, possibly more if you’re wanting to have separation between your dahlia plants for ease of deadheading or cutting flowers.
We don’t do anything too special other than that - just keeping them well watered until they sprout up.
4. Growing Out
Once you’ve planted your tubers, you basically have to sit back and wait until the first shoot pokes up out of the soil. Especially if you live in an area that gets a lot of precipitation, it’s best to keep your tubers on the dryer side - so that they don’t drown and start rotting. We only start watering once the dahlias are actively growing and the shoots are poking out of the soil.
Dahlias require plenty of water and nutrients. When given plenty of both, they’ll produce well for you - but restrict either, and you’ll end up with sad, stunted, nonproductive plants. They are actually surprisingly drought tolerant - their large tubers store a lot of moisture for short periods of time - but ultimately you’ll want to ensure that they aren’t restricted by a lack of water or nutrients.
You can use fish emulsion or kelp fertilizer to keep them well supplied with nutrients. While some people like to perform a foliar spray and others like to use an in-line fertilization system, we like to do it the old fashioned way - in a watering can near the base of the plants. We do it once every couple of weeks to ensure they get a nice boost of nutrients so they can keep pumping out blooms.
From here on out, the dahlias will grow pretty easily - they’re actually one of the easiest flowers that we grow. One important point is that if you’re growing for cutting the flowers - especially if you’re a flower farm or growing for design, you’ll want to pinch out the dahlia.
The reason for this is that you have a choice when growing dahlias - you can choose to either have a few very large flowers, or lots of smaller flowers. Much likev when you’re growing determinate tomatoes, if you want to have a few large flowers you pinch off all the runners and side shoots so the plant can focus more energy into the few flower buds it has.
On the other hand, if you pinch the “lead” shoot when the dahlia is just a few inches high, the dahlia will reroute it’s energy to start developing a lot of very vigorous side shoots that will give you an abundance of flowers all season long.
Dahlia exhibitors would be horrified to see you pinch the lead, but it’s something that all flower farmers do to ensure that they get numerous long-stemmed blooms.
Lastly, as your dahlias grow, it’s important to keep them upright and straight as possible. We can get away with not corralling our dahlias because we have them planted so densely, but you may want to stake them if you’re growing them far enough apart that they can’t support each other. You can use a bamboo or willow pole, or a T-post can also work if you want to ensure that dahlia won’t be going anywhere.
Most of our dahlias start blooming at least by the end of July and so long as we keep them deadheaded, they will continue to bloom nonstop until the end of October at least.
Dahlias are one of our most valuable flowers we grow as flower farmers - both for ourselves and other floral designers. For this reason, we take special care to harvest dahlias using an exact method to ensure that we get the maximum amount of blooms.
When cutting dahlias, you want to do this either very early in the morning or late in the evening - this reduces the risk of wilting and ensures that you get the sturdiest and long-lasting blooms possible. We cut directly into a bucket of deep cool water to ensure that they get hydrated well. I’ve also seen a new recommendation to pierce the dahlia just above the last joint- to allow water to fill the last “section” of the stem which allegedly helps the dinnerplate dahlias last up to a week. We’ll see if that works, I’ll let you know more this summer.
Dinnerplate dahlias tend to have a very short vase life - a few days at most, so we harvest as close to the last minute as possible to give either ourselves or our floral designers the maximum amount of time possible. Although it’s recommended sometimes not ot harvest dahlias until they’re fully open, we ignore that rule - harvesting dinnerplate when they’re about halfway open, knowing that they will open more after harvest and in the vase.
It’s important to keep dahlias deadheaded. Even if you don’t use the flowers, make sure to cut off the dead blooms, and try to cut as close to the base as possible to ensure that you continue to get nice long stems for all future blooms.
That’s it for growing dahlias. Like I mentioned, dahlias are one of the most productive plants you can grow in a cutting garden or on a flower farm - if allowed to keep blooming without a killing frost, they’ll continue to bloom for upwards of twenty weeks! Their blooms are stunning and a people pleaser whether tucked in the border, arranged in a vase, or wrapped with silk ribbon into a bridal bouquet. If you’re not growing dahlias yet, you should be!