Dahlia Overwintering

The results!

Plastic tote full of peat moss and dahlia tubers

Last autumn, I tried my hand at storing my dahlia tubers over the winter. The results of the experiment are in. I had partial success.

Last year in September, I inspected my dahlias and decided it was worth a shot at digging up the tubers and storing them. Dahlias are not hardy tubers so they cannot take freezing. In my part of the country, the soil freezes down at least a foot, so if I leave the tubers in place, they will freeze and die. The thing to do is to lift them up, clean them off and store them.

The lifting went extremely well. They are shallowly rooted and at that time, a strong stem was growing out of them. You can wait until the tops have been frozen off by frosts but I just pulled them out a bit early. I trimmed the tops of into a recycling bag, and cleaned up the tuberous root mass. The roots look like either a single sweet potato, or if growing well, a starfish shape of lots of sweet potatoes joined at a big stem. Where the tubers join the central stem part is where the new buds will grow. I tried not to break up the starfish too much. If a tuber breaks off without the shoulder going into the stem part, it will not grow any eyes (buds) next spring.

I spread out the tubers on newspaper in the garage and waited a few weeks until all the soil was dry and dusted off. Then I filled two experimental containers with peat moss.

The main container was a plastic fliptop tote. I started with a layer of 3 inches of dry peat moss in the bottom. Then I tried to lay out the tubers in a single layer without letting them touch each other. I filled in the spaces with peat moss and repeated layer upon layer until the box was full. This box was stored in a closet in an unheated garage next to a heated wall of the house. I was going for a cold but not freezing location. I placed a max/min thermometer on top of the box. Over the course of the winter it was fairly stable and cool, but it dig reach a low of 26 degrees and a high of 62 degrees. Only about 30% of the tubers survived the freezing temperature. I got 11 tubers suitable for planting this spring out of 36.

My other small container only held 2 tubers but they did the best. I put peat moss in a gallon sized ziplock and tossed in the tubers. I squeezed the air out and stored it all winter in the vegetable drawer of the refrigerator. They came out perfect because they did not freeze. The only problem was room to store all the tubers I want to store. Two tubers took up the whole vegetable drawer of the refrigerator, so that is not practical except for a few special ones.

Unearthing the tubers in the spring was kind of a mess with peat moss going all over and rotten tubers being pulled out. I am not sure if all 11 planted tubers are going to be successful. Some of them had a few arms that were questionable. I probably should have trimmed them off but if they die, they die. They are planted in cool soil now but we are getting some warm weather in the next two weeks. It is May 9th here and our 90% frost free date in this part of the country is May 15th. I doubt the tubers will grow any shoots out of the ground to get frozen in the next couple weeks. Here are some photos of the tubers as they came out of the plastic tote.

I guess I will be visiting the dahlia society sales to augment my collection this spring.


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