By Pam Rosendal, Colorado Master Gardener
Who hasn’t marveled at the beauty a dahlia, gladiola or canna adds to the summer garden? Did you know it is possible to store those tender bulbs over the winter to enjoy that same vibrant display next year? It is and here’s how.
“Tender bulb” is a generic term used for any summer blooming bulb, rhizome, tuber or corm that will freeze and die if left outdoors during a Colorado winter. Some examples include dahlia, calla lily, elephant ear, gladiola or a four o’clock.
After the first light freeze kills the plant foliage, dig up the bulbs on a warm (50+ degrees) day to protect the bulbs and roots from cold damage. Carefully dig up the bulb and the roots using a shovel or pitchfork. Be very careful not to damage the bulb. Wounds to the bulb can allow fungi or bacteria to enter, causing rot during winter storage. For the same reason, it’s a good idea to wear gardening gloves while digging up bulbs to avoid scratching or nicking them with your fingernail. Tender bulbs must be dug up before the ground freezes.
Once the bulbs are out of the ground, clean off as much excess soil as possible. It’s unnecessary to wash the soil from the bulbs or roots; they need to dry as quickly as possible. Check the bulbs for any shriveled or dead parts or any that are soft or oozing. Again, these are prime candidates for rot and should be discarded. Cut the plant stems or stalks two to three inches above the top of the bulb. Cutting the stem flush with the top of the bulb will also create an entry point for rot. (Noticing a theme here?) To label, use a marker to write on the stem, stalk or bulb itself.
Place prepared bulbs into a container, being careful not to damage or bruise them. Keep them in a warm, dry place until the outer surface of the bulb dries and toughens much like curing a fresh potato. Turning the bulbs occasionally will facilitate this drying process, which can take up to two weeks for larger bulbs.
After drying, it’s time to tuck the bulbs away for their long winter’s sleep. Place them in newspaper, sawdust, peat moss or vermiculite in a ventilated box. Store them in a cool place (45-50 degrees) ensuring they don’t freeze. With our dry winter air, a bowl of water nearby will add humidity. Check in on them every now and then during the winter to monitor for rot or excessive drying. For more information, check out PlantTalk or the CSU Fact Sheet on summer blooming bulbs.