Procedures for storing dahlias and gladiolus are very similar
Lifting dahlia tubers and storing them for planting next spring can be a challenge because they often rot or spoil in storage. After the first frost when the dahlias' foliage turns black, let them adjust to dormancy for a week. Cut back the foliage and stem to within 6 inches of the ground. This makes it easier to see the base of the dahlia and where you will need to spade around the plant. Insert your spade carefully into the soil a safe distance from the stems so as not to sever the tubers. After spading all the way around the plant base, gently lift the tubers out of the ground. Clean off as much dirt as possible, and let the tubers dry in the sun for a day or until they are dry. They may be left in the sunlight but must not freeze. After they have dried, get rid of any dirt which was left, and cut the stem to 1 inch, and trim away any skinny and hairlike roots. This will minimize the chance of fungus. Place them in boxes and cover with sand, peat moss or sawdust to keep them from drying out. Store in a cool, frost free place at 40-50 degrees. Check the tubers monthly to ensure that they are not rotting (too cool or wet) or shriveling (too warm or dry). If too wet, remove them from the box and allow them to dry out before repacking. If too dry, add a little water to the packing mix.
Similar procedure for gladiolus
Gladiolus corms also need to be lifted once the foliage has been killed by frost. Shake off the excess soil and sort the corms by cultivar. Cut the stems off just above the corm. "Cure" the corms for about three weeks in a warm, dry, airy place. At this point, the corms you planted in spring will easily break off the bottoms of the new corms that developed over the summer growing season. Discard the old, spent corms and save the new ones. Leave the husks intact. Place the new corms in paper bags, cloth sacks, or nylon pantyhose legs. Store them in a well-ventilated place that is dark, dry, and cool. Ideal storage temperatures range from 35-45 degrees. The cooler the better, as long as they are not allowed to freeze.
When you dig the corms, you will notice a number of miniature corms attached to the main corm. These are called cormels. They should bloom in two or three years if you save them and replant them each spring. Save only the largest ones, those at least ½ inch in diameter. Next spring they should be planted about 1 ½ to 2 inches deep, then dug up, and replanted a second and third year. A lot of work, but if you have a glad you really like, it may be worth it to you.
Thoughts of winter
I don't mean to be pessimistic here talking about frost, but we need to take care of our perennials so that we can enjoy them next spring. That is why northern gardeners are so enthusiastic, they get this winter vacation from outdoor gardening, where they can just dream and plan the perfect garden next year! So after about two or three hard frosts, we can cut back our perennials to 3-6 inches with a pair of hand pruners. This keeps harmful insects and pathogens from finding a safe place to spend the winter. Plants like sedum, ornamental grasses, coneflowers, and black-eyed Susans, provide winter interest as well as food for wildlife. In the spring all perennials can be cut down to the ground, but now the 3-6 inch stumps help to remind us where the plants are located. The debris from these plants can be put into the compost pile if they are healthy.
Plants infested with a pest or disease -- or those prone to such afflictions -- do not go into the compost pile. The dead leaves of plants like hosta, that can harbor fugitive slugs and snails, or plants like phlox, or anything plagued with powdery mildew, or blight, go straight into the trash to prevent the problems from being reintroduced into the garden next season.
Usually the first part of November, after at least three hard freezes, and you know perennials are dormant, insulate them by covering their crowns with a 2-3 inches deep layer of dry leaves. Evergreen boughs will also protect plants. Hold them in place with an 8-10 inch long anchoring pin, or a rock placed on top of the boughs will keep them secure. The mulch prevents frost heaving and premature bud break in the spring. If the mulch is put on before the plant is dormant, it may smother the plant or encourage disease to develop.
Kyle Schulz is a Wadena County Master Gardener from Sebeka, and the regular gardening columnist for the Wadena Pioneer Journal.