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How to grow Dahlias

Dahlias are spectacular flowers for both the garden and arrangements, so it’s no surprise that they are a regular staple in our floral arrangments. If you have been wowed with these spectacular flowers, we’re sharing our secrets so you can learn how to grow dahlias too!

Variety of dahlia styles and colours
A variety of dahlias of different styles and colours.

Choosing dahlia varieties

With over 20,000 different cultivars, it can be easy to get overwhelmed with choosing the right dahlias for you. All the beautiful varieties that we offer are the ones we’ve had success growing here in southern British Columbia (specifically the Fraser Valley) and are disease free. We only offer a select few tubers in the form of whole clumps for a limited time in October. 

Flower arrangement with Dahlia 'Cafe au lait'
Flower arrangement featuring the Dahlia ‘Cafe au lait’

How to store your Dahlia tubers in winter

Once you have your tubers, there are a few important steps to ensuring that you have beautiful blooms next summer and fall.

Overwinter storage: there are many different ways, but the basics remain the same. The tubers need to be stored in a cool, semi-damp, dark environment. For us, the ideal spot is our crawlspace. For you, that is ideally somewhere between 5 and 15°C, 75 to 85% relative humidity, and dark. Maybe the beer fridge?! Many have had success with an unheated garage, barn or shed, although we’ve lost tubers that were stored in an uninsulated shed. The most important point: the tubers cannot tolerate below zero. Ever.

To maintain humidity we harvest and cure the unwashed tubers, (allowing the remaining soil to hold the needed moisture.) We add pine shavings to each paper bag and ensure good airflow. Other techniques are using crumpled newspaper, peat moss, or vermiculite, and storing in cardboard boxes. The tubers need to remain below 15°C, otherwise you’ll wake them up too early. Have you ever had potatoes start to sprout in the back of your pantry?!

Protect the neck and crown. Unlike potatoes that seem to sprout all over, the dahlia tubers need that precious neck and crown undamaged. This is where your new plant will grow from. A nice plump tuber without a neck or crown will simply turn to mush once planted, no matter how nice you talk to it! Larger clumps can definitely be divided into smaller sections, as long as you have a healthy tuber, neck, and crown. 

Dahlia tubers, dug up and grouped in large paper bags.
Dahlia tubers: all bagged up and prepped for sale.

When to plant your dahlias

Plant the tubers in the spring after the last frost date (April 15 around here), in good soil (about one hand-width deep, about 4 hand-widths apart), where they will have at least six hours of sunlight a day. Let the spring rain do the watering. This is important, around here they can, yet again, turn to mush if they are over-watered before you see green growth.

How to care for your dahlias

Protect from slugs!
One reason you may not be seeing new green growth is because the slugs love snacking on these tender shoots. This could be somewhat helpful in the technique that we call pinching back. If properly done, we pinch off or snip the lead branch down to a lower set of leaves. This counter-intuitive task stimulates the side shoots which provides much more practical stems for cut flower arranging. 

Stake your plants.
Staking materials can be anything from a tomato cage, to the classic method of using grandma’s pantyhose and a post. 

Once the dahlias start blooming, we harvest every three days (full length stems); that will ensure fresh blooms on strong stems from July until October.

Ideally your well-drained garden soil that was amended with your home-made compost is all you’ll need. Too much nitrogen fertilizer will only result in growing a nice green shrub with barely any flowers. Water only when needed.

Floral arch featuring dahlias in red, yellow and orange
Round arch decorated with dahlias.

Harvesting dahlias

Harvest in the cool of the day, when the blooms are open (they don’t tend to open any further) but the petals are not yet papery on the backside. For best vase life, use fresh clean water and keep the vase out of direct sunlight and heat.

When to dig up your dahlias

In the fall you can dig up the dahlia tubers in mid October or after the first frost. In our climate, some people have had success leaving the tubers in their garden under a heavy bed of mulch. I’ve had variable success with this. Most often the ‘ugly’ colour that I left for dead is the only one that makes it through the winter!

Fun fact about dahlias

Did you know that dahlias are edible? Apparently you can cook the tuber just like a potato, and use the petals for garnish!*

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*Disclaimer: The author, Lexi Richards has researched dahlia edibility, however, individuals consuming the flowers, plants, or tubers listed on this web page, do so entirely at their own risk. Neither the author nor Twiggage & Bloom can be held responsible for any adverse reaction to the flowers. 

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