CO-Horts Blog

Friday, May 15, 2015

Totally Tuber: Planting dahlias in your garden

Posted by: Alison O'Connor, Larimer County Extension

I'm stepping up my game this year at the Larimer County Fair. I've entered nearly every year since I started working for Extension and love the competition, the judges' remarks and the sheer chaos of entry day. But I've never entered much in the Open Class Flower Show, primarily because I don't feel my flowers are worthy. Insect damage, bleached petals and misshapen foliage does not make the cut in our judge's eyes. Plus, there are really, really good flower growers and they actually know what they're doing.

But this year I bought dahlias. I grew a few several years ago and they were surprisingly easy, low-maintenance plants. But I had tucked them in a bed on the side of the house and didn't enjoy them much. Then I got an email from an Oregon dahlia company..."Sale! 50% off! Buy dahlias now!" So I did.

For those who haven't attempted the "summer-blooming bulbs", here's a quick lesson in planting dahlias. Don't be scared--they're really no different than a daffodil or tulip. Yes, they do need to be dug from the ground in fall (they are not winter hardy in Colorado), but properly stored and cared for, dahlias (and their folk) can last for years.

I purchased a mix of flowers from the "Cut Flower Collection" and also a group from the "Itsy Bitsy Collection". I figure that by the time the Fair rolls around, I should have enough flowers to scrape together an arrangement. And the names are the best part! Some of my cultivars include 'Bride to Be', 'Lights Out', 'Bambino' and 'Angels of 7A'.
Each tuber comes stamped with the variety name.
First of all, read the instructions sent by the grower. They know what they're doing and what's best for their plants. One of my favorite things about dahlias is that they don't need to be watered following planting--only after sprouts appear above the soil surface.
Planting instructions attached to the dahlias.
Carefully inspect your tubers and make sure they are firm without any signs of rot. If they have sprouted, you can snip back the new growth to a length of one inch. This will not hurt the dahlias and will actually encourage better growth.
Cut back new growth to 1" in length.
I have a sunny location in my garden where all the plants died over the winter (except for the silver lace vine, which nothing can kill). A perfect location for the dahlias. I raked back the mulch, squealed at the amount of worms I found and started digging. Dahlias need to be planted flat on their side 6" deep and 18-24" apart. The plants can get quite large at maturity (anywhere from 12" to 5+ feet; taller plants will need staking) so proper spacing is necessary.
Pulling back the mulch to expose the soil.
Plant dahlias flat on their side in a 6" deep hole. Space tubers 18-24" apart.
Digging each hole was getting cumbersome, so I stepped up production and dug a trench and placed the tubers, properly spaced, in the trench.
The dahlias are planted and ready to cover with soil.
Now, because I always forget where I plant my bulbs, I decided to mark where they were planted with a golf tee. (Of which I have many on hand.)
Handy dandy golf tees to mark where the tubers were planted.

We have a new addition to our household, Maple. She is a rescued research beagle from Colorado State University and she is ALL PUPPY. Curious about everything and learns something new about the world every day. I didn't realize she would have such an interest in the dahlia tubers. I should have known. Now I'm worried that she may be inclined to dig them up, so I bought some fencing.
Maple meeting a tuber for the first time.
I covered all the tubers with soil, added mulch (in a thin layer) across the planting areas and marked each one with a golf tee. Now I just have to wait a few weeks for growth. Let's hope it stops raining.

And if you don't have garden space, dahlias can easily be grown in containers. Just follow the same spacing and depth requirements mentioned above. Also consider the mature size of the plant and your container size--ensure it's big enough to support the plant at maturity (generally a 12" by 12" container will be large enough). Cover the tuber with a few inches of soil and water it in. Be careful about watering until growth starts...but don't let the potting media dry out. Also make sure your media is well drained so the tubers don't rot. You'll also need to fertilize throughout the summer.

Dahlias are great container flowers. Just make sure your container is large enough to support the plant when full grown.
Later this fall, I'll be sure to post about what to do to harvest and keep your dahlias for next year. I'm sure Maple will be a great helper. For the official CSU Extension Fact Sheet on summer-blooming bulbs, click here.
Maple requested the pansies.
I'll remove them as the weather gets too hot and just allow the dahlia to grow.


  1. I do hope the dahlias you planted will match your fingernail polish!

  2. I read your story yesterday and went to my garden center and bought dahlia tubers for the first time. I thought that dahlias were only for expert gardeners. You gave me the confidence to try them. I bought one called Smarty Pants and one called Magic Momment. I'm worried that we are going to get too much rain today in Rochester. We might get a half inch. Will that be bad for them since they arent supposed to get watered after you plant them? My soil is very sandy. I go to the dahlia show every year at the MN state fair and never thought I could grow dahlias like that in my yard. Thank you for the instructions on how to grow them.

  3. Hi Rita, a fellow Minnesotan! You may want to wait a couple days for the soil to dry out a bit. If it's too wet, it may cause the tubers to rot. More importantly, it's not good for your soil to be walked on when it's too wet. You can easily plant the tubers into the beginning of June and have a good flower crop. Good luck! Keep me posted on your success.

  4. Nice post for decor your home with plants and planters.