(Editor's Note: This article was originally published on February 23, 2009. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
Tubers fall into two groups: root tubers and stem tubers. Stem tubers are the result of thickened rhizomes or stolons, which produce shoots and grow stems and leaves at the sides of the parent plant. Examples of plants grown from stem tubers are Cyclamen and tuberous begonia.
Root tubers make up the larger group of familiar garden plants. Root tubers are alive, but dormant, storing nutrients during the non-growing season. They come out of dormancy either due to temperature or length of day.
The following familiar plants are grouped according to how the tubers should be cared for after the growing season.
Sweet Potato Vine (Ipomoea)
Bear in mind that, unless you enjoy the work of digging and replanting every year, most of the above specimens can simply be replaced each spring. Economically speaking, digging your tubers is the best way to save money and propagate those plants you like the best.
Leave in the Ground
To ensure survival through the winter, tubers left in the ground should be heavily mulched in the coldest Zones. Additionally, when planting any tuber, take care to locate it in an area that drains well. Excess moisture is the tuber's greatest enemy, causing rot and a climate for disease. The plants mentioned above all benefit from cutting back the foliage when it begins to yellow in fall.
Tips for Digging, Treatment, and Storage of Dormant Tubers
- For those mentioned above, be sure to wait on digging until the first hard frost blackens or softens the leaves. The tuber needs this time to draw nutrients from the leaves and stems, in order to remain viable through dormancy. Freezing temperatures will damage the plant parts above ground, but will not harm the roots or tubers.
- Before a hard freeze (25˚F or below ), carefully dig the tubers, taking care not to cut too close.
- Place the tubers, or clumps of tubers, in a dry warm spot to begin the drying process. When the soil around the roots has dried completely, gently remove it, being careful not to damage the tuber.
- If a tuber has been broken or chopped with the shovel, wash it off, let it dry thoroughly, then dust with antifungal powder.
- If you have large clumps of tubers, such as those produced by cannas, divide them using a sharp knife. Since a tuber will not sprout unless it has at least one "eye," you must divide the tubers accordingly in order to get regrowth. Eye's are pink or white dots or bumps on the top portion of the tuber (as opposed to the bottom where you'll see roots).
- Give the prepared tubers a little longer to dry completely. They should be placed in a sheltered area that won't freeze.
- It's a good idea to treat the tubers with fungicide before storing.
- Most tubers can be simply stored in vermiculite, perlite, or sand in a cardboard box. Some growers use the ventilated plastic bags that are found in grocery store produce sections, but plastic can retain moisture and you stand the chance of losing your tubers to rot. Canna tubers can be wrapped loosely in newspaper and laid in a cardboard box with plenty of space between the packages.
- Store tubers in a dry cool area with a steady temperature of between 35 and 50 degrees Fahrenheit.
- Check the tubers twice during the storage season: once in December and once in March. Remove any tubers that show signs of rot or mold.
With an understanding of tuber physiology and some patience, you can have magnificent blooms year after year.