Overwintering Summer Bulbs
by Diana Alfuth, horticulture educator for Pierce & St. Croix County UW-Extension
Summer bulbs cannot make it through our cold Wisconsin winters. If you want to plant them again next year, tender bulbs must be dug and stored once the foliage begins to yellow or is killed by frost. Cut the foliage to about 2 inches, dig the bulbs with a spading fork and knock off most of the soil. Don’t wash canna, dahlia or caladium bulbs, but hose off others, if needed. Discard any bulbs with spots or sunken areas, which may indicate the presence of disease.
Once bulbs are dry, pack them with some peat moss, sawdust, perlite, vermiculite or sand, or put them in thick paper bags and place them in a cool, dry place for winter. A root cellar, unheated basement or extra refrigerator can be used to keep temperatures between 50 and 65ºF, or 35 to 55ºF for gladiolus. Don’t store bulbs with ripening fruit, such as apples. The fruit gives off ethylene gas, which can damage bulbs.
Check the bulbs periodically over the winter. If mold is present, spread the bulbs out to dry or otherwise reduce humidity. Separate the bulbs prior to planting next spring.
Planting Summer Bulbs
from The New York Times column ‘Garden Q&A’
Summer bulbs are tropical types that want summer conditions. They will start sprouting when the soil is still less than toasty, but if it is downright cold, they’ll sulk, and if they sulk in soil that is damp as well as cold, they’re likely to rot.
So people in short-season areas have two options: the first is simply to wait for warm weather and then wait for flowers; the other is to give plants like crocosmias, acidantheras, and dahlias a short head start indoors.
Since you don’t want to have to worry about providing greenhouse conditions, wait until it’s near the frost-free date, then plant your summer beauties in a free-draining seed-starting medium like Pro-Mix. Water well, then set the pots (or for small bulbs, plug flats) where they will be warm but not hot, 60º to 65ºF. Add water only as necessary to keep the soil barely moist, and do not fertilize.
It should take a couple of weeks before sprouts show above the soil and start needing light, by which time the weather should be warmer. Set the plots outside in a sheltered spot where they will get plenty of sun but be protected from cold winds, and be prepared to move them indoors if the temperature threatens to go below 55ºF. Once you’re sure the weather has settled in a warm direction, transplant into the garden.