If the weather in your area has led to a hard freeze (temperatures that are sufficiently cold, for a long enough period, to seriously damage or kill seasonal vegetation), it is time to dig up your sensitive bulbs. Certain plants that grow from bulbs do excellent in the Treasure Valley, but can’t survive our cold winters.
Cut Them Back
Cannas and Dahlias are two plants that fall into this category. With a little effort, you can enjoy your sensitive bulbed plants year after year. After a hard frost cut the stalks down to 8-10 inches above the ground. This stem will give you a handle to work with when you loosen the bulbs from the soil.
Wait 10 days before you dig, this will allow the bulbs to harden off and the stem a chance to dry out. After 10 days, use a pitch fork and loosen the soil on each side of the stem. Be sure to leave at least 1 foot of space on each side of the stem to ensure that you do not pierce the bulbs.
With the soil loosened, you will be able to lift the stem and bulbs out. Wash all the dirt from the bulbs and set them out to dry. If the temperature will be below freezing at night be sure to cover the bulbs with a blanket or sleeping bag at night. After 2-3 days the bulbs should be dry enough for storage.
Pack the bulbs in vermiculite in a box. It is important that moisture does not build up in the box, but that the bulbs are also protected from drying out. Store the bulbs in a basement or a protected garage. The bulbs must be protected from freezing.
If you check the bulbs every few weeks during the winter, you will be able to make sure they are doing ok. If you see any mold, powdered sulfur can be dusted onto the bulbs to stop its progress. Temperatures should range from 35-45 degrees. In the spring when you are ready to replant the bulbs, they can be separated if necessary.