Dahlia planting season…
… is in full swing for dahlia gardeners and growers across Canada. Depending where you are, you might be just starting, right in the middle, nearly done or done! We’re in the nearly done camp… and that always feels good when you can stand straight up for awhile. Along with planting season, it’s also “still a risk of frost season” in many places across Canada.
Our frost-free date in Terrace BC is usually around mid-May. We started planting out the dahlias on May 10th. The 2 week forecast looked pretty mild with a low risk of any frosty mornings so in my excitement some of the first varieties I put in the ground were some of my favourites that I started early indoors. They already had a fair bit of beautiful green growth exposed above the soil line. Risky! Because those weather forecasts? They change a bit sometimes and ours did! The forecast for the morning of May 31st, after a relatively warm day on the 30th, showed temps going down to 1 degree celsius with clear skies. A recipe for frost…Eek!

What to do?
We’re worried about the cuttings and early starts that we’ve planted. If cuttings get frosted, they are lost. If an early started tuber’s growth is frosted, the green foliage will wilt when it thaws and die off, but if the tuber is in good shape it will likely send up new growth albeit set back a couple weeks. We’re not at all worried about the tubers that have been planted that haven’t broken thru the soil yet. That is one of the reasons we prefer planting eyed up tubers as opposed to cuttings.
Learning about how frost forms is really interesting and its really useful knowledge to have if you’re a gardener or a farmer. I haven’t found a really reliable weather forecast for frost in our area. So in lieu of that I rely on my own observations. If we have a very warm or hot sunny day, followed by clear skies over night and early morning temperatures above zero but less than 5 degrees celsius, there is a high likelihood that frost will occur in exposed areas.
There are a few things you can do!
- Do nothing! Pay your money, take your chances. But give it some thought! If you’ve got cuttings planted and you get a frost, you will most likely lose those plants.
- Don’t plant your early starts or cuttings out in the field until all risk of frost has passed! i.e. if you’ve got space to keep them going in a greenhouse, do that.
- Cover up all the dahlias that have growth above the soil line. Frost cloth is nice to have on hand. It’s extra work to get out there and cover everything up… but it might be in your best interests. If you just have a few plants, you can cover them up with big pots. Covering plants traps the radiant energy (like cloud cover does too) from escaping that causes surface temperatures to cool rapidly creating frost.
- move your plants to a sheltered area – only really feasible if you’ve got a few in pots
- Get the sprinklers out! That’s right! It works. Adding water to the equation can help protect your plants from a frost.
What did we do?
On the evening of May 30th, we used overhead sprinklers to ensure all the dahlia beds were well watered. We did not put out any frost cloth. We did not move any plants that had been set out to harden off if they were in relatively sheltered spots (i.e. alongside a greenhouse, under the canopy of a tree etc.). Your risk tolerance for loss along with experience will help guide you. We want to minimize both loss and the amount of extra work we have to do. Sometimes that means having a loss here and there for those “I won’t do that again” lessons.
The results?
On the morning of May 31st I did a walk around and observed that we did indeed have a light frost! The leaves of our strawberry plants were frosty, there was visible frost on the grass in exposed areas. How bout the dahlias? They were all ok! Not a single plant was lost. Yay!
During my walk around, I noticed one very interesting anomaly! The lid of a big rubbermaid tub full of baling twine had collected water from the overhead sprinklers. There was a skim of ice on top! ICE!!! On top of the tub I had set out a dahlia that I had been growing in its own container for the past month. The water was frozen, but the dahlia was not! The leaves just had a heavy dew on them. Neat! Puzzling! Science is cool and the dahlias are alive and well!

Ice formed on the top of the rubbermaid container full of baling twine even though the air temperature was just above zero.

The dahlia growing in the plastic tub set on top of the rubbermaid container had heavy dew on its leaves, but did not get frosted!































































