Monday, 15 February 2016

Gothic Green Thumb: Growing Dahlias

Growing and keeping dahlias in your garden

It's mid-February and the majority of us are at home avoiding snow. I'm sure the last thing on your mind is gardening, but this is the month when many green thumbs begin to grow their seedlings indoors, in preparation for the spring. I'm no different as I am preparing to plant two of the dahlias I winterized last fall. This is earlier than usual, but the forecasts indicates we'll likely have an early spring and I'd like to get a head start (I usually plant them in the beginning of March).

Before I lived on my own, I tried to grow a garden outside my bedroom window at my parents' house. This was often unsuccessful as the sun never quite reached that area and many of my plants became leggy and weak. Last year, I lived in a house with a big open backyard that got a lot of sun (sometimes this was to my detriment, as I loathe treeless places and sunburn easily). I foolishly assumed that any old plant could be put in my backyard, which wasn't the truth at all! Somehow I became lucky with the flower selections I had made. My most triumphant plant yet has been the dahlia. This is a flower that is both hardy and beautiful and comes in a variety of shapes, sizes and colours. The dahlia fares well in the Canadian climate and if planted early enough it can provide months of gorgeous pom-pom shaped blooms, well into October!

Starting Indoors

If you're new to growing dahlias, I strongly recommend that you start your seedlings indoors in the month of March or early April. Although starting indoors isn't necessary, I've found that this is the best option for those living in damp unforgiving climates. It's also better for those who have issues with critters invading their garden.

First, let's talk bulbs! Dahlia bulbs are called tubers, they look a little like potatoes and are typically sold in clusters. A good dahlia tuber will be firm and feature eyes, just like potatoes. If a tuber is wilted and squishy it's probably not going to be viable. Some gardeners suggest that wilted tubers can be revived by soaking them in water for a few hours, prior to being planted. If your tubers are moldy they should be discarded. When buying tubers, inspect the packaging thoroughly for signs of insects or mold, you can tell when a tuber has gone bad. Like most any bulb, tubers should be planted in well drained potting soil. You'll want to use an 8" pot or larger for each plant. When you plant the tubers make sure you have 1" of soil lying on top of them. If you're planting a cluster of tubers, you'll want the crown (where the plant is growing out of, not the roots) to sit closest to the top of the planter. Keep the top of the soil about 1" from the rim of the planter.

Do not water the tuber until the first signs of the plant are emerging above the soil. You can start fertilizing your dahlia once it's about 3-4" tall. Your seedlings will require a good deal of sunshine, so place them in an area that receives about 8 hours of sunlight a day.

Maintenance & Outdoor Growth

Maintaining your dahlia shouldn't be too difficult once it's begun growing. If you've been growing seedlings indoors you'll want to transplant them into pots or in the ground once it's warm enough. It's recommended that you plant after the last frost and when the ground is 60°F (15°C). A good potting soil will serve you well. I learned the difference between the cheap stuff and the pricier soil very quickly, in this case it is better to spend more and get the better soil. Don't cheap out! Watering can vary from one to two times a week, to even more than that. Last year it was so hot that I had to water my dahlias every day. I advise watering from the bottom up instead of overhead, as too much overhead watering can encourage rot in the tubers. I save fertilizing my dahlias until June after planting in late April or early May. I do it once every two weeks for all my plants and it's been successful. When your dahlia has grown about four sets of leaves, pinch the next growing set off. This sounds terrible but it helps the plant put energy into growing outward instead of upward. Once blooms have developed, you will have to start deadheading. This is the same technique as before, you just pluck the dead blooms off by pinching beneath them (do you remember popping off dandelion heads? Same thing). Deadheading will encourage flower growth and result in more blooms so don't be afraid to do it!


Although I once read you should bury the tubers with a thick layer of mulch on top, I'm hesitant to leave anything out over the winter. Our winters are terrible in Southern Ontario, we can get five feet of snow one moment and then temperatures will spike and we'll have flooded basements and soggy yards. It's just not worth the risk. It's better that you unearth your tubers and bury them in a box of mulch or perlite, and keep them indoors in your basement or an area that's on the cooler side. I failed to store my Vincent dahlias two years ago and the tubers rotted right through, I was heartbroken as this was my favorite plant.

Start by cutting your dahlias back after the first frost. Dig the tubers up and separate them. Look for "eyes" like you would on a potato, that's always a good sign. Make sure you don't damage your tubers during this process, be gentle. Before you put them away for the winter you want to dry them a little. Last fall my tubers were fairly wet and needed to be dried for a few days. You don't want to leave them too long, otherwise they'll dry out completely and become unusable. Some of you may find it takes a week before they're just right. Finally, fill a box with mulch and place your tubers inside. The mulch will keep the tubers just moist enough that they won't rot but they won't be growing all winter either. There's a degree of dormancy you want to maintain, so I don't recommend wetting the mulch before hand. Just use it straight out of the bag, if you find it's particularly moist then give it time to dry out some. Mark which dahlias are which using a popsicle stick. Throughout the winter check on them periodically. If you're concerned they're too dry and showing signs of wilting, mist the mulch with a spray bottle. If you see signs of mold, separate and discard the spoiled tubers and then change to a drier mulch.


Through my experience dahlias have been a very easy plant to grow and maintain. I think it's a wonderful flower for beginners, and given the variety of types and colours there's enough to suit even the most unusual colour palettes! There are plenty of blood red and purple blooms to satisfy your gothic green thumb.



  1. Very informative post! Thank you! I love gardening. I grow a lot of Russian Sage and hostas. I have to admit, I really don't like hostas, but they grow easy! LOL! I want to get more flowers in my garden!

    1. Thanks, I'm glad you enjoyed this post. I've never tried Russian Sage, but it looks awesome! I can't grow much of a garden at my current house, everything has to be potted so I'm limited in what I can grow. We had hostas at our last place. They're a resilient plant and easy to care for, but like you I don't care for them much. I think it's because they're too easy lol, everybody has them.

      I've really enjoyed growing dahlias and roses over the last few years. I also grew morning glories and petunias, but I'm not sure I'll have enough sunlight for either plant at the new place. I might have to grow my garden at my parent's house again lol.

  2. I actually never tried to grow Dahlias :-O there are some really pretty ones out there though!


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