Breaking tuber dormancy

SteveM

Even with ideal temperature and moisture, the ability of a tuber to break dormancy depends (at least in part) upon the conversion of starch into sugar during tuber storage. This conversion seems to be related to the length of time in storage and the temperature in storage. Longer time and/or colder temperature during storage speed the conversion.
I did a quick, non-scientific experiment to test the influence of cold temperature on dormancy. After digging, washing, dividing and drying Hollyhill Lilibet clumps, I chose 16 random tubers and divided them into 2 groups of 8 tubers. Each group was stored dry in a one gallon pot wrapped in a plastic bag. One group was stored outside in the shade and the other group was stored in my refrigerator. Day temps outside ranged from 60-70F and nights 45-55F. Refrigerator temp was about 40F. After 5 weeks I planted the tubers in a shallow flat with soil barely covering the tubers and eyes. After 6 weeks outside, it was obvious the cold-stored tubers sprouted much earlier (3 weeks) than the other group. All 8 of the fridge tubers sprouted but, so far, only 3 of the ambient temp group
(Tubers on left side were stored at ambient temp, tubers on right were stored in fridge.)

A real study would involve a lot of variables to find the best combo of temp and time. But this might be food for thought for anyone who has not had much luck bringing tubers out of dormancy soon after digging (e.g., to take cuttings).

Bessie

SteveM Thanks for the info and taking the time to run a test. This is very timely information. I've been wondering what to do with all the clumps(didn't divide any) that have not yet broken dormancy. Sounds like I need to pack up the ones that haven't shown any signs of sprouting and put them into my refrigerator in the garage, to take a little "rest'. Seems like a novel idea to employ cold stratification on Dahlia tubers! This idea could be the reason most of the dahlias left in the ground over winter(9b zone) have already pushed sprouts up..

SteveM

Bessie Did you ever try your idea to artificially inject a tuber with sucrose to induce sprouting? Comparing it to a cold treatment might make an interesting comparison experiment.

My father (in Montana) used to say he had a problem getting tubers from Southern states to sprout. I'm guessing a lot of Northern growers get somewhat of a cold treatment before they even dig their tubers, especially those who get a frost before they dig. I'm not aware of any study that has determined the parameters of cold treatment that will yield the best results. Same thing with "time": How long should tubers be stored to convert the starches to sugar, regardless of the storage temperature.

If I let a plant go dormant before I dig it, then it will be almost impossible to eye it out to take Winter cuttings. If I want to take cuttings of a variety from my field I have to dig the plant before it goes dormant, cut it back to about 1.5 tall, pot it up, and place under "long day" lighting.

Bessie

SteveM I would believe anything your dad hypothesized, especially about how it's hard waking up tubers from southern states. I have not used the 1% ethanol( think cheap vodka) and 1% sucrose solution, as a spray I on treatment, so far this year (reference). I actually forgot about it until your discussion. I've had such a disaster with my seedlings this year, and trying crazy stuff, I've tried to restrain myself! I have sprayed the tuber clumps with a BTI solution in the wake-up process. The two nemeses in my gardening are fungus gnats and gophers.

BarryO

To wake up overwintered tubers, we find placing them in zip lock plastic bags with alittle moistened Pro Mix accelerates both sprouts and hair roots.