Force spring bulbs into indoor winter blooms

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Last Updated: 
November 23, 2005

CORVALLIS, Ore. - Autumn is the time for planting bulbs indoors as well as outdoors. By potting up some bulbs in October or November and “forcing” them to bloom early indoors, you can have a running supply of fragrant and fresh flowers in the house all winter.

Paperwhite Narcissus, hyacinths, daffodils, crocuses, and certain types of tulips can be coaxed into bloom indoors well before their normal outdoor blooming time.

Choose high quality, plump heavy bulbs from varieties recommended for forcing, recommends Jan McNeilan, Oregon State University Extension consumer horticulturist. In many cases, the catalog or bulb carton at the garden store will indicate if a bulb is suitable for growing indoors.

Plant the bulbs in fertile, well-drained soil in clay pots with drainage holes. An equal mix of garden loam or potting soil with peat moss and a bit of sand for drainage is a good mixture for forcing bulbs. Plant bulbs more closely together than in an outdoor garden. A six-inch pot could hold five tulips, three hyacinths or nine crocus. Leave about an inch of space between the bulbs. Most bulbs should be covered to their tips with soil. Allow about a half an inch between the top of the soil and the pot for watering. Water thoroughly after planting.

Once the bulbs are planted, most types except Paperwhite Narcissus need several weeks of cold and darkness to allow roots to form. Place the pots in an unheated garage, basement, shed or cold frame, ideally at about 35 to 48 degrees. Or the bulb-filled pots can be buried in the garden up to the pot top then covered with a few inches of straw or sawdust.

Keep the soil moist, but not wet, by watering about once a week. Different kinds of bulbs have individual requirements and are ready to bring indoors at different times:

Crocus - Plant about one or two inches deep. Store in cold and dark for about eight weeks.

Daffodils - The top of these bulbs should be about an inch below the soil surface. Place in cold storage about eight weeks.

Paperwhite Narcissus - These can be forced into bloom without cold storage right after purchase if the bulbs have been given a cold period to break dormancy. Ask your dealer. Simply place bulbs in bed of pebbles, gravel or soil and add water up to root disk of bulb. Place in sunny window. Keep at cooler temperatures (50 to 60 degrees). Fragrant flowers will bloom in about four weeks. For a continuous series of blooms, start new bulbs every two weeks, storing unused bulbs in the refrigerator.

Tulips - Only certain varieties of tulips will force well. Ask your nursery worker or read bulb cartons for advice. Plant bulbs with the flat side toward the pot, about one-half inch deep. Store in cold and dark for 12 weeks.

Hyacinths - Plant bulbs one-half inch below the soil surface. Store in dark, cold place for about eight weeks. Then bring inside to a warmer (70 degrees) dark place, such as a closet. Water occasionally. When the leaves grow 8 inches tall, move the plants to a sunny window or well lit area.

Scilla, grape hyacinth, freesias, and some types of lilies can also be forced into early bloom. Consult a complete gardening guide for more information.

Bring bulbs indoors any time after they have developed a good root system. Don’t shock the bulbs with too much heat and light all at once, advised McNeilan. Place them in a cool room with dim light for a week or so. Then put the bulbs in a sunny room until the flowers open. To make the blooms last longer, move the bulbs into a cool room at night.

If cared for properly, most forced bulbs can be planted outdoors and coaxed to bloom again in a year or two. After the forced bulbs bloom and fade, gradually reduce water, and place in a cool room or shed. Plant out in the garden as soon as the ground can be worked in the spring.

Author: Carol Savonen
Source: Jan McNeilan