Forcing Bulbs for indoor blooms in Winter

bulbs forcing

Why not enjoy your favorite spring bulbs all winter long? With a little extra attention, you can grow many bulbs indoors. While paperwhites and amaryllis are ready to plant and grow, all other bulbs must be cooled for a time to fulfill their winter dormancy requirements before they will flower. This cooling process is often called “forcing” and is intended to mimic the action of nature outdoors.

Planting: Choose a pot shallow and wide enough to hold several bulbs. Place a layer of stones or other coarse material in the bottom of the pot, set the bulbs in root side down, then fill the container with fine stones, sand, light potting mix or other material until the bulbs are about two-thirds covered. The bulbs already contain all the nutrients needed to bloom once, and too rich a soil may cause them to rot. Water up to the base of the bulbs. Or use a hyacinth glass: Fill with water to the base of the bulb, and do not let it get dry.

Cooling: After watering, cover the pot with plastic, punch a few holes for circulation, and place in the fridge (this works well because the temperature is consistent, just be sure to keep the bulbs away from fruit). Or, place them in a garage, unheated basement, root cellar, outdoors covered with 6-8" of leaves and earth, or other dark place at 35-40°F. The bulbs will not be hurt by light frost but will be harmed by heat or a hard freeze.

Bulb Genus weeks of: cooling indirect light
Anemone, Crocus, Chionodoxa, Galanthus, Leucojum, Scilla 8-12 1-3
Iris reticulata, Muscari, short Narcissus 10-14 2-3
Hyacinthus. tall Narcissus, Tulipa 12-16 2-4

The bulbs are ready when you can see roots at the bottom of the pot, and leaf tips are beginning to emerge. Bring the bulbs into a cool area (50-65°F) with plenty of indirect light to encourage leaf growth. Too much heat at this point will cause premature flowering; do not place near radiators or wood stoves. Keep the soil moist, but do not overwater.

When 3-5" of leaf growth has appeared, bring the pots into direct light to encourage flowering. Once blooms have appeared, remove pots from direct sun to keep blooms from fading quickly.

Plant forced bulbs out in the garden in spring, or let them go dormant in their pots and plant them in fall. They will not force well a second time. The bulbs may not blossom until the 2nd spring after they were planted outdoors.