Growing Dahlias – An Easy Guide for Home Gardeners

Growing dahlias can be a rewarding experience for any home gardener. Their beautiful blooms take center stage in our flower garden beds in late summer and continue their show until the first frost. Whether you’re a beginner gardener or an experienced gardener this article is for you if you’d like to add these gorgeous stately flowers to your flower gardens.  Are you ready to grow some beautiful dahlias? Let’s get started!

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Have you ever seen Dahlia plants in pots at your local garden center? Yes, they have the small border or pot dahlias, but I’m talking about the tall variety. Likely not. So to have these beauties in your flower gardens, in all likelihood, you need to grow them from tubers.

Common Questions About Dahlias

First of all, let’s answer a few common questions about dahlias.

Are dahlias easy to grow? Yes, absolutely. Even a beginner gardener can grow dahlias. 

Do dahlias come back every year? Yes and no. Dahlias are winter hardy only in the warmer climates. So in USDA hardiness zones 7 and below, dahlia tubers must be dug up and stored over winter. Stay tuned and we’ll give instructions for this later in this post. As an alternative to overwintering dahlias, you can treat them as an annual flower, do nothing and leave the tubers in the ground all winter. The tubers will decay and become organic matter for the soil. 

Different Categories of Dahlias

There are probably 1000s of different dahlia varieties and they are classified by size and form.

Dahlia Classification by Flower Size:

• Miniature (up to 4 inches in diameter)
• Small (4 to 6 inches)
• Medium (6 to 8 inches)
• Large (8 to 10 inches)*
• Giant (over 10 inches)*

*Large and giant dahlias are often referred to as “dinner plate” dahlias.

In addition to the size of the flower, different varieties of dahlias grow at varying heights.

Dahlia Classification by Flower Form:

• Single: Single row of petals around a central disc
• Collarette: Small ruffles around the disc
• Peony: Multiple rows of petals with no visible central disc
• Anemone: Tubular petals on top of larger, flat petals
• Ball and Pompon: Globe-shaped with tightly rolled petals
• Cactus and Semi-Cactus: Pointed petals, curled or twisted

How to Plant Dahlia Tubers

The instructions for planting dahlia tubers are the same for planting in containers or planting in the ground.

For this section, we will assume that you have purchased new Dahlia tubers. When you open the package, the tubers should be dry and firm like a potato, but not shriveled. The tuber should not be mushy or smelly. If that is the case, pitch those tubers or return them. The same is true for dahlia tubers that you over-wintered.

There will be a crown with an old stem and the tubers will hang from that. You may or may not be able to see eyes on the tubers up around the crown. Those little eyes or growth buds will grow into new stems.

For a single tuber to be viable, it needs to have a neck (sometimes referred to as the crown), an eye and the main tuber. Yes, you can grow a beautiful dahlia plant from a single tuber. If the growing conditions are right during the first year, the plant will produce more tubers and just keep multiplying every year.

Just like with many flowers and perennials, dahlias like to grow in fertile soil with good drainage. And, to live their best lives and reward you with lots of blooms, they need to be planted in full sun. 

Dig a hole deep enough so the tuber can be placed on its side or standing up with the crown or stem pointed up. 

Bury the entire tuber so that the crown is covered by about 2 inches of soil. 

This might sound a little intimidating especially if you are new to planting dahlias. If the tubers are in good shape, your dahlias will grow, even if you don’t place them exactly right. Just be sure to get the crown or the stem facing up and they will be fine.

Water your planting area well and wait. It can take up to 2-3 weeks before you see signs of growth.

Planting Time – When Can Dahlias be Planted Outdoors

Dahlia tubers can be planted outdoors in the spring after the danger of frost has passed in your area and the soil has warmed to around 50 degrees Fahrenheit. 

How to Get a Head Start Growing Dahlias

Because I live in zone 4b/5a and our growing season is relatively short, my preferred method of growing dahlias is to start them in early April in my portable, pop-up greenhouse. If you don’t have a greenhouse, and you have the room, you can start them indoors.

When the weather has warmed up and we’re past frost danger, the young plants are already 1 to 2 feet tall and have a head start over dahlias that are just being planted.

The basic planting instructions are the same as above. Start with a 1-gallon nursery pot and add a few inches of a quality potting mix to the bottom of the pot. Then place the dahlia tubers (with the tubers hanging down from the crown) into the pot and fill in around the tubers with potting mix, covering the crown or stem with about 2 inches of soil. If you are planting a single tuber, lay it on its side with the eye facing up. I gently water the freshly planted tubers and then fill in with more soil where the soil has settled.

Whether you pot your tubers up early, or plant them directly in the garden, it can take up to 2-3 weeks for new shoots to start showing, so be patient.

For more ways to get a jumpstart on more flowers grown from bulbs or tubers, be sure to check out this post when you’ve finished up here.

Dahlia Care During the Growing Season

Once you’ve gone to the work of planting dahlias, it’s important to take proper care of them. 

Watering Dahlias:

Dahlias like moist but well-drained soil. The tubers can take up a lot of water, but they will rot if the soil stays wet. During dry periods, water your plants deeply at least twice a week. They need a minimum of 1 inch of water per week. Use a rain gauge or a small container to determine how much water your dahlias are getting.

Fertilizing Dahlias:

Dahlias work hard to produce those big lush blooms and are thereby considered heavy feeders. There is a lot of mixed information about the best formula for fertilizing dahlias, so I’m just going to share what I do. When I pot up the tubers in the spring, I plant them in a potting mix that has fertilizer in it.

When I plant them in the ground, I add a scoop of Osmocote, a slow-release fertilizer, and mix it into the soil. Depending on the ground soil, I will also add a shovel of compost. During the summer, I put my dahlia bed on the same fertilizing schedule as my annual flowers and container plantings and fertilize every 2-3 weeks. 

The Importance of Staking Dahlias in Your Garden

Once you have your dahlias planted, it’s important to add a stake right away. Dahlias grow quite tall so it’s necessary to have a tall stake. I like these stakes. As the plant grows, continue to tie the stem to the stake.

If dahlias aren’t staked the tall stalks will fall over and break with the weight of the heavy flower heads or strong winds. Often times without stakes the main stem will grow crooked and be unable to stand on its own. Don’t skip staking your plants.

I like using tomato cages too to stake dahlias. Especially those growing in pots.

Growing Dahlias in Containers

Yes, dahlias can be grown in containers. In fact, I believe the easiest way to grow dahlias is in containers. Here’s how to do it:

Select a container that is large enough to sustain the growth of the tubers and resulting root system. I like to use containers that are 14” or larger with adequate drainage holes.

The planting directions are generally the same as if you are potting up tubers in the spring. Fill the container about 2/3rds of the way full of a good quality potting mix that contains fertilizer. Place the tuber in the middle of the container, with the crown or the old stem on top and the tubers hanging down. If it’s one tuber, just lay it on It’s side with the eye pointing up. Then just fill in around the tubers and cover with about 2 inches of potting mix. Water well. Let the soil dry before watering again. 

Once the tubers or plant is planted, I put a tomato cage into the container to support the dahlia as it grows. 

I usually fertilize my dahlias growing in pots every 2-3 weeks during the summer.

How to Overwinter Dahlia Tubers

If you’ve never attempted to overwinter dahlia tubers, I want to encourage you to give it a try. Once you have it down and working well in the environment where you store them, the tubers get bigger every year and can be divided so you have more plants to share or sell.

There are many different ways to overwinter dahlia tubers, so I will share some of those and share what has worked for me. This can be trial and error because not everyone’s storage situations are the same. You will have to experiment to see what works for you.

At the end of the growing season, you can wait until frost zaps the dahlias, or dig them a few days before the first fall frost in your area.

Step 1 – Using loopers, cut down the dahlia plant leaving about a foot of stem. This makes it easy to handle the clump of tubers. Go ahead and make a bouquet of the remaining flowers.

Step 2 – Dig up the dahlia tubers. I highly recommend using a garden fork for this chore. I find that damage to the tubers is minimal when I use a garden fork instead of a shovel. 

Step 3 – If you have the time dahlia tubers can be rinsed off and cleaned. Otherwise, clean off any excess soil with your hands and allow the tubers to dry. Do not store damp tubers because they will likely rot or grow mold. 

Storing Dahlia Tubers

This is where success or failure comes into play. There are several ways to do this and you will have to experiment and see which way works best for your situation. 

• Store the tubers in peat moss or vermiculite in a plastic bin.
• Lay out the Dahlia tubers in a crate.
• Store the tubers in peat moss or vermiculite in a plastic ziploc-type bag.
• Simply store the tubers in a plastic grocery bag and loosely tie the top. This is how I store my dahlia tubers.

No matter which method you decide to use to store your dahlia tubers, they need to be stored in a cool, dark place. The ideal temperature for dahlia tuber storage is between 40 – 50 degrees Fahrenheit.

Not only do temperatures of the room have to be just right, humidity levels are important too. If the storage area is too humid, the tubers will grow mold and rot. If the storage area is too dry, the tubers will shrivel and dry up. 

Many dahlia growers say that they check on their stored tubers every few weeks throughout winter and spritz them if they are too dry. I just have to be honest here and say this is just not practical advice for me or most home gardeners. If you have the time and care that much about your dahlia tubers, then by all means check on them during the winter.

Ways to Propagate Dahlias

Growing Dahlias From Seed

Dahlias can be grown from seed. I’ve grown small, border or pot-type dahlias from seed and they are fairly easy to grow. I start the seeds indoors. 

We don’t have a long enough growing season to grow taller varieties from seed, so I have never done that. Floret Farms has a very good tutorial for growing dahlias from seed. 

Dividing Dahlia Clumps

As dahlia tubers grow year after year the clumps can become quite large. To keep them healthy, it’s important to divide the clumps. I used to be a little bit intimidated to do this, but it’s really difficult to ruin a clump of dahlia tubers and easy to divide them with a sharp knife and garden shears.

Remember all you need for a dahlia tuber to be viable is a crown (or neck), an eye and a healthy tuber body. If you want to learn how to divide dahlia tubers, this is a good video on YouTube.

More Tips for Growing Dahlias

Young dahlia plants can be decimated by slugs. To avoid slug damage, I suggest sprinkling Sluggo around the area where you planted your tubers, or plants. If you already know you have slug problems in your gardens, consider planting your dahlias in a container.

When planting your dahlia tubers or plants leave adequate space between the plants for good air circulation.

Are dahlias a good cut flower? Yes and no. If you grow dahlias for your own satisfaction, then yes they are lovely cut flowers and I grow them in my cut flower garden. Many flower farmers sell cut flower bouquets with dahlias, and while they are stunning, cut dahlias don’t last in a vase for more than 5-6 days. You can extend their vase life a little bit by using cut flower food, but only by a few days.

If you would like to learn more about growing dahlias, this book might be what you are looking for. It’s on my wish list.

I hope you’re leaving today with the education you need to grow dahlias in your flower gardens. Are you going to start growing dahlias? Or perhaps, you already grow dahlias, but you’ve never overwintered them. Are you going to try overwintering your dahlias? Leave a comment below and let me know. Also scroll back up and save your favorite dahlia pictures to your gardening board on Pinterest to remind you of this post later.

Happy Gardening, 
Joanna

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