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Reviewed October 1993

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Contents

• Forcing bulbs in soil
• Step 1
  Preparation stage
• Step 2
  Potting stage
• Step 3
  Rooting stage
• Step 4
  Top-growth stage
• Step 5
  Bloom stage
• Forcing bulbs in water

Related publications

• G6511, Care of Flowering Potted Plants
• G6610, Spring Flowering Bulbs: Daffodils

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Spring Bulbs for Indoor Blooming

Ray R. Rothenberger
Department of Horticulture

Bulbs made to flower at other than normal times are said to be "forced." The practice is commonly used to flower daffodils, hyacinths, tulips, crocus and other spring bulbs during the winter. With proper planning and care, bulbs can supply color for the home from late November until early April when they begin to flower normally outdoors.

Forcing bulbs in soil

Steps for forcing include selecting most suitable varieties, potting bulbs properly in well-drained soil, providing proper cold temperature treatment, bringing bulbs into a cool room and moving the plants to a display location when well developed.

Step 1
Preparation stage

Any spring flowering bulb can be forced, but to be successful, select types and varieties known to be good forcers. Hyacinths and daffodils are generally the easiest. Tulips are slightly more difficult, but with proper treatments they can be forced successfully. Many small bulbs such as crocus, grape hyacinth and snowdrops also may be forced.

The general procedure for forcing all these bulbs is similar. Purchase only top quality, flowering-size bulbs for indoor forcing. Good bulbs contain ingredients necessary for successfully producing roots, leaves and flowers.

Hyacinths
These are usually the most easily forced spring bulbs. They may be forced in water or potted. Potting should be done in late September or early October. Plants will flower about one month after being brought indoors from the chilling treatment. Earliest bloom from bulbs can be expected about mid-January.

Specially prepared bulbs are available for forcing into bloom by Christmas. Specific directions are supplied with these bulbs if they are prepared for early forcing.

Table 1 lists hyacinth varieties most suitable for forcing along with the appropriate potting and forcing dates.

Table 1
Hyacinth varieties for forcing

Spring Flowering Bulbs — Daffodils.

The varieties most suitable for early forcing are Rembrandt, Cragford, Golden Harvest, King Alfred and Carlton.

Paperwhite narcissus are suitable for earliest forcing either in pots or in water.

Tulips
Table 2 suggests tulip varieties suitable for forcing, but many others may be used.

Table 2
Tulip varieties for forcing

All varieties should be potted before the end of October for adequate root growth and chilling. Dates listed in the table are the earliest that bulbs planted in October should be brought into forcing conditions. Most varieties flower about one month after being brought indoors, although there is variation due to varieties and individual forcing conditions.

Step 2
Potting stage

Materials
The following materials will be needed for potting bulbs:

• Pots 4 to 8 inches in diameter. Pots shorter than regular pots, known as azalea or bulb pots, should be used.
• Soil mix of one part garden soil, one part sand and one part peat. High fertility is not essential, but good drainage is important. No fertilizer is needed at potting time.
• Gravel or small stones for drainage.
• Labels of wood, plastic or metal.
• Thermometer for checking temperatures.

Procedure
All bulbs are normally potted in October.

• Place a 1-inch layer of gravel in the bottom of the pot to ensure good drainage.
• Add enough soil mixture to fill the pot so bulbs are placed as follows:

Daffodils
Plant so about one-half of the bulb will be above the soil line.

Hyacinths and tulips
Allow only the tip of the bulb to show above the soil line.

Small bulbs (Crocus, Snowdrop, Grape hyacinth, etc.)
Plant so they will be about one inch below the soil line.

• Set the bulbs in the pot. One large bulb may be placed in each 4-inch pot. Use six tulips, three hyacinths, five daffodils or 15 crocus (or other small bulb) to each 6-inch pot.

Tulips should be placed with the flattened side of the bulb toward the outside of the pot. All bulbs in a pot should be of the same kind and variety to ensure uniform flowering.

• Fill around the bulbs with soil to the proper height and firm it with light pressure. Avoid tight packing of soil. After planting, the final soil line should be about 1/4 inch to 1/2 inch below the rim of the pot.
• Label each pot with variety of bulb, date of potting and expected date to begin forcing.
• Add water until it drips through the drainage hole in the bottom of the pot. After about one hour, dump out any remaining water in the saucer.

Step 3
Rooting stage

After potting, keep hardy bulbs where temperatures range between 35 and 48 degrees Fahrenheit — 40 degrees Fahrenheit is ideal. This may be a cool north room, basement, crawl space, bulb cellar, outdoor trench, refrigerator or cold frame.

An unheated basement or storage cellar is most convenient because temperatures don't fluctuate greatly and the cooling is quicker and more satisfactory. An old refrigerator may be used for a few bulbs.

A cold frame is easily built outdoors and may later be used for other gardening activities. Place the pots to be forced in the old frame and cover them with sawdust, straw, leaves, peat moss, shredded styrofoam or other material. The cold frame should be in a shady place or on the north side of a building so the soil is as uniformly cool as possible in October and November. No sash is needed on the cold frame.

When preparing only a few pots, place them on the surface of the ground close to a building. Cover them with peat moss, leaves, straw or similar material and invert a box or bushel basket over them for protection.

Bulbs stored outdoors will normally get sufficient moisture from the soil around them after initial watering. Indoors they should be kept moist at all times. Overwatering, however, may cause bulb rot.

Roots should develop soon after potting. Excellent root growth is essential to good growth and flower formation. Potted bulbs should be placed outdoors at least three weeks before the first hard freeze is expected. This is an important period for good root development.

Step 4
Top-growth stage

A few varieties may be brought indoors after about 12 weeks of cooling, but most will require 13 or 14 weeks to develop the necessary roots and top growth. Indoor forcing requires three to four weeks. To extend the bloom period, remove potted bulbs from storage at weekly intervals.

If soil and tops are frozen when they are brought indoors, place them in a cool room (about 40 degrees Fahrenheit) for two or three days to thaw out slowly. Don't touch the plant tops when they are frozen.

If plants are not frozen, bring them directly to a cool, bright window where temperatures range close to 60 degrees Fahrenheit. Don't place them in direct sunlight. Keep bulbs watered, but fertilizer won't be needed.

Step 5
Bloom stage

When flower buds are almost fully developed, pots may be moved to the living room or other area in the house where they are to be displayed. Avoid placing them in full sunlight or close to heaters. The life of the flowers can be lengthened by moving the plants back to a cool room at night.

Bulbs that have been forced indoors are usually of little value for outdoor planting and should be discarded.

Forcing bulbs in water

Tender types of narcissus such as "Paperwhite" and "Soleil d'Or" don't require cold treatment before they may be forced into bloom. These are the most popular and dependable bulbs for forcing and may be grown in water with pebbles for support.

Hyacinths can be forced into bloom in containers that will support the bulb with only its base touching the water. Bulbs should be cleaned before placing them in glasses. The best time for starting the bulbs is in October.

The glasses containing the bulbs should be kept in a cool (45 to 50 degrees), dark location until tip growth is 3 to 4 inches long and the flower cluster emerges free from the bulb. This may take 8 to 12 weeks. When the top growth is well developed, move the glasses to a cool, bright window.

G6550, reviewed October 1993