Replanting dahlias in Colorado

Question: I have a number of beautiful dahlias that I removed and put into storage after the first frost last year. Fortunately or unfortunately my basement is not below 50 degrees but my garage gets to ~15 degrees on really cold nights, so I don't have an ideal storage location. I stored them in my basement but some of them have already begun with large shoots. I pruned the shoots and moved the tubers to my garage, but I'm not sure even that will last until after our last frost (which last year was almost June!) 

So here's my question: I have a sun room in my house that I can put containers into, so would it be possible/advisable to start the plants there in the Spring and then move to my gardens once threat of freeze has passed? Or should I just keep cutting the shoots and plant them in May?

responder: Adams County Master Gardener  Replied March 16, 2023, 3:26 PM EDT
response: Hi Justin,Thank you for your Dahlia question. You are correct, your garage is too cold and your basement is a little too warm for ideal storage. However, there is more to storage than temperature. Be sure the tubers are also kept in the dark, at the right humidity, and not touching.Have you considered storage in a refrigerator as suggested in this fact sheet https://s3.wp.wsu.edu/uploads/sites/2073/2014/03/102607.pdf ?  In addition to being a controlled temperature this would also keep the tubers dark. A similar approach is mentioned by the American Dahlia Society in their storage guide: https://www.dahlia.org/docsinfo/articles/digging-dividing-and-storing-tubers/ To your main question, we recommend focusing on proper storage rather than starting your dahlias indoors in containers and transplanting them outside.  Dahlias typically prefer "full sun" which is nearly impossible to obtain indoors without serious grow lights. Without adequate sun, the dahlias will grow up weak and "leggy" and struggle to hold up to the stress of transplanting. Further they will likely need several weeks of hardening off before they can handle May or June outdoor sunlight. It isn't typically worth it.If you need to get your dahlias into the soil as soon as possible, be sure to monitor the soil temperature especially overnight. Your garden may have a microclimate which warms up earlier in the season, and allow you to get planting.

responder: The Question Asker Replied March 17, 2023, 12:31 PM EDT
response: Thanks for getting back to me and for the guidance. The refrigerator won’t work very well for me since I’ve got around 20 of them and most are 10-12” across, so I’d need a couple refrigerators for dahlias alone in my garage! I think next Winter I’ll keep them in my garage but add a small batch of lights for warmth on the coldest nights. For the indoor planting, we have a very bright sun room (see attached) with south facing windows, so I’m wondering if placing them in there will provide enough light? I may test it with a few this Spring and then I’ll know for next year. Appreciate your advice!Thanks,-Justin Justin Crandallm: 512.318.0570  |  e: <personal data hidden>  |  LinkedIn  On Mar 16, 2023, at 1:26 PM, Ask Extension <<personal data hidden>> wrote: