Growing Concerns 591: Storing roots for the winter


Saving cannas, begonias and other tender plants


Dear Janet,

Please tell me how to keep my cannas over winter. Last year I dug them up after the first frost even though the leaves had not turned brown. I then knocked the dirt off each; some I split into more plants and let them sit in the garage until early December. I then put peat moss in boxes, laid the plants on top and covered them with peat, newspapers and burlap.

This spring when they were uncovered, all were soft and mushy. Someone said they should have been thoroughly dried and placed in the basement in a cool dark spot, not an unheated garage. - M.A. -

Dear M.A.,

There are at least three options for saving cannas:

Canna as houseplant

One, grow them as houseplants. Pot them up and bring them in. Do not pot them in garden soil, which often leads to root rot. Use soilless potting mix, which provides far better drainage in a pot than even the best garden soil.

Bare root storage

Two, cut the tops back whenever you like. Dig out the root mass and let it dry stem-side down in an airy, frost-free place, until most of the soil will fall away. Wrap the unbroken root mass in newspaper and put it in a paper bag in a dark, 50- to 55 degree place with 50 per cent humidity.

Alternatives to newspaper wrapping are to bury the roots in a box of sand or barely moistened peat.

The idea is to keep roots cool and dark so they don't start growing again, padded against bruises and nicks that could open the flesh to fungus infection, and moist enough that they don't dry and die. Old-time, dirt floor, unheated Michigan basements or "root cellars" are ideal for storing roots. Modern basements are usually too dry and warm, so the keeper has to check stored roots now and then to add a few drops of water or remove sprouted and rotten clumps.

Root cellar or root pit

Option three was once standard procedure on some farms to save root crops like potatoes or carrots for winter consumption. Dig a pit three to four feet deep, so that its bottom is below the frost line. Put your roots into the hole, then backfill it with loose, dry leaves or straw, mounding it a couple of feet high. Then cover all of that with a tarp, a board or soil and let Nature care for your plants.

If rodent damage is likely, line the hole with hardware cloth or a metal garbage can. Put in straw, the roots, then more straw or leaves. When you fill the can or reach the top of the hardware cloth, put the lid on the can or bend the sides of the hardware cloth down.

Your cannas rotted for two reasons. They went into storage injured. Every cut is an injury, a place where rot can begin during storage. Cut up roots only as you replant in spring. Also, the roots were not sufficiently insulated. Keep them in a root cellar, Michigan basement or storage pit.


Dear Janet,

When should I dig up my caladium and begonia roots and how do I store them for next season?


Dear S.,

Dig them any time now. Use option one or two from the preceding question.

Don't use option three, as a storage pit may become too cold for caladium and begonia. Several years ago volunteers stored some of our tender roots this way. In spring, the cannas and dahlias looked as they had when we first buried them but the more tender caladiums and tuberous begonias had rotted.

Short reports

Recent explosion of mealybug and indoor plant problems no surprise.

Turn on some grow lights! Many people have complained about how gray it's been this fall, but few have thought how that might be affecting the plants that subsist on window light. Less light means less energy and less energy means the plant can't fend off or hold down populations of its parasites.

You can wash pests off, pluck them off or kill them with an insecticide but they'll be back in force if you don't find a way to give that plant more light.

Bearded iris, forsythia, azalea or lilac blooming in fall?!

It's not unusual. Plants that bloom very early in spring often have internal timers that tell them when to bloom, mechanisms triggered when a period of cold is followed by a warm-up. Such a species may require 500 hours of below-40 temperatures to "think" it has been through winter, then will bloom at the next respectable warm spell. Later blooming species may need 1,000 hours of cold or that plus additional environmental cues before they flower.

Given the cold we had this past spring, which chilled plants after they had bloomed and grown for a time, some plants with short-winter triggers had nearly met their cold requirement by Labor Day. A few cool fall nights, then a warm up, and the buds open.

Don't be alarmed. Such plants rarely "waste" all their flower buds in fall, and sustain no lasting injury from the precocious show.


Green thumbs up

to spreading slow release organic lawn fertilizer now. It goes further than any other fertilization toward improving a lawn's health.


Green thumbs down

to blowing, shredding, mowing or grinding if you can rake, quietly. Your ears and your neighbors will thank you.


Originally published 11/6/04