Expert: Long Island Gardener - 2/13/2007

Question
Thank you for your response.  To answer your questions: 1)The mold is mostly white or light grey. 2)After I dug them up I did let them dry for well over a week before I took them to the storage unit. 3) They do not appear to be soft or black at this time. 4) I stored them in bushel baskets as I always have, no plastic bags. 5)The unit has probable gone from the 40-50's when I put them away to maybe in the teens just recently as our weather has taken a dive. 6) My basement generally maintains the low 60's as I also store my geraniums and other plants down there.
Thank you again for your help and suggestions.  I now have them in the basement again and will watch for the next month or so to see what happens. Any suggestions as to weather I should try to remove the mold by washing or scraping or ??
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The text above is a follow-up to ...

-----Question-----
For the first time ever I stored by cannas bulbs in a public storage unit instead of my basement.  I've noticed that there is now mold on the bulbs. Is the mold from cold or humidity? What can I do to save them.  They are well over 50 years old.
-----Answer-----
You didn't describe the color of the mold or your pre-storage measures.  Were these stored without heat?  Do they appear they black, soft and/or rotting in addition to the mold?  Did you use plastic bag(s) to store them this time?  What do you think the temperature was in this storage facility and how warm was it when you had them in the basement?

Cannas should always be air dried for a week in a warm location before you put them in storage.  Then tuck them into a cardboard box and store.  Some people use peat moss or vermiculate, but I find this unneceesary.  Cool, dark, humid storage with plenty of ventilation (which means NO PLASTIC BAGS) is always best.  Your damp, dark (I assume) basement was ideal.  I suppose that's how you have kept these for a lifetime.  And I appreciate your concern.  Please review the questions above and let me know asap any answers you can provide.  Meantime, keep them warm, dark, and dry.

Answer
Any below-freezing exposure would probably do at least some injury to your Cannas.  How much damage depends on the length of exposure and how cold it got.

Still, you did not mention any mushy, canker-type, festering wound that would result from the frigid temperatures.  This mold is most certainly growing over wounds or decaying growth.  As a precaution, soak them for 5-10 minutes in a solution of 1 part bleach : 10 parts water.  Don't make the bleach solution too strong - the Canna tissue is tender and injures easily, and too much bleach will burn the tissue.

Canna rhizomes, like Dahlias, are still active when you lift them out of the ground, unless you have waited for a total killing frost.  Since they are headed into dormancy this is not usually a problem, although responses vary by Canna variety - as they do with Dahlias.  Rhizomes grow somewhat differently from bulbs and dorms; when one is finished blooming at the end of the season, the natural cycle is for it to generate new Rhizomes and go dormant. Kept cool, without top growth to stimulate metabolism, Rhizomes continue to grow through the winter in your basement or storage unit or garage all depending on the temperature you keep them in.  Adjusting for lower temps of course will keep metabolism slowed.  The perfect storage specs would hover around 45-50 degrees F.  High humidity keeps them from drying out, but prolonged moisture is asking for trouble.

By the way, there was an error in my previous email.  I said you should "keep them warm, dark, and dry".  I should have typed instead: "keep them warm-ER, dark, and dry".

Very interested to know how these turn out.  Keep in touch -and if you have any more questions please ask.  There's a lot to cover here.