Forcing Spring Bulbs Indoors

Few things are more welcome to avid gardeners then the first flowers of spring. This highly anticipated event can be advanced well ahead of its normal date by forcing bulbs indoors, and now is the time to plan for the process, given the ready availability of bulbs. “Forced” bulbs are those that are induced to flower at other than their normal time. This practice is commonly used to flower narcissus, hyacinths, tulips, crocus and other spring-flowering bulbs during the winter. The process is relatively simple and involves five basic stages or steps.

Step 1: Preparation stage. The general procedure for forcing all species of spring bulbs is similar and starts with purchasing only top quality, flowering-size (large) bulbs. Good bulbs contain the stored reserves necessary for successful production of roots, leaves and flowers.

Hyacinths. This species is considered by most to be the spring bulb easiest to force and may be forced potted or in water. Potting should be done in late September or early October. Plants will flower about four weeks after being taken out of the chilling treatment (described later) and brought indoors. Narcissus. The cultivars of narcissus most suitable for early forcing include Rembrandt, Cragford, Golden Harvest, King Alfred and Carlton. Paperwhites are a form of narcissus and can be forced without chilling either in pots or water.

Tulips. While any cultivar of tulip can be forced into flower early, some are more suitable than others. Table 1 lists cultivars of tulips especially suited for early forcing. Tulips should be potted before the end of October for adequate root growth and chilling. Most cultivars flower about four weeks after being removed from chilling treatment and brought indoors, though there is variation according to cultivar and forcing conditions.

Step 2: Potting stage. Whatever the species, bulbs usually are potted in the month of October. Use azalea or bulb pots 4-8 inches in diameter, according to the species being forced. Although equal parts of garden soil, peat and sand can be used, excellent results can be obtained through the use of soilless media containing primarily sphagnum peat, perlite and vermiculite. These mixes have the advantage over soil of being biologically inert and possessing better drainage properties. Add enough potting medium to fill the pot so bulbs are planted as follows: 1) Narcissus. Plant so about one-half of the bulb will be above the soil line after watering and settling. Use five bulbs per 6-inch pot. 2) Hyacinths and tulips. Allow only the tip of the bulb to show above the soil line. Use three hyacinths or six tulips per 6-inch pot. Tulips should be placed in the pot with the flattened side facing toward the outside of the pot to insure a uniform flower display. 3) Small bulbs (e.g., crocus). Plant so they will be about 1 inch below the soil line. Use 15 bulbs per 6-inch pot. Label each pot with cultivar of bulb, date of planting and expected forcing date and water thoroughly.

Step 3: Rooting/chilling stage. After potting and watering, keep hardy bulbs where temperatures will range around 35-40 F. This might be a cool north room, basement, bulb cellar, outdoor trench, cold frame or refrigerator. If the latter is used, food products should not be stored in the refrigerator while the bulbs are being chilled. The purpose of this stage is to allow bulbs to produce a healthy root system and to elongate their flower primordium in advance of being forced to bloom. If placed outdoors in trenches or cold frames, bulbs should be exposed to at least three weeks of favorable temperatures (around 40 F) before the first hard freeze occurs. Most cultivars will require 13-14 weeks of chilling treatment to develop necessary root growth and flower primordium development being forced into flower.

Stage 4: Top-growth stage. The actual forcing of the plants into flower indoors adds an additional 3-4 weeks, depending upon species and forcing conditions. If the potting medium and tops are frozen when they are brought indoors, place them in a cool room at about 40 F for 2-3 days to thaw out slowly. If the plants are not frozen, they can be brought directly into a cool, bright window where temperatures are in 60 F range. They should remain in this environment until nearly ready to bloom. Bulbs must be kept watered during this stage, but fertilization is not necessary.

Stage 5: Bloom stage. When flower buds are almost fully developed, pots may be moved out of the bright window into the living room or other area of the home they are to be displayed and enjoyed. Avoid placing them close to the heater or in direct sunlight. The life of the flower can be lengthened by moving the plants back into a cool room each evening. Unfortunately, bulbs that have been forced indoors are of little value for outdoor planting and probably should be discarded after their bloom period is over.

It is possible to lessen the doldrums of a typical Missouri winter by getting an early start on spring. Forcing spring bulbs indoors is not difficult, and now is the time to start planning for a colorful, flower-filled January and February.

Table 1. Tulip cultivars suitable for forcing.

Apeldoorn	orange-scarlet	Jewel of Spring	yellow-streaked red
Apricot Beauty	salmon-rose	Kansas	white
Attilla	purple-violet	Make Up	red-edged white
Bellona	golden yellow	Merry Widow	white-edged red
Blizzard	creamy white	Olympic Flame	yellow-flamed red
Christmas Gold	deep yellow	Orange Nassau	double orange
Christmas Marvel	cherry pink	Orange Wonder	bronzy-orange
Couleur Cardinal	cardinal red	Paul Richter	scarlet red
DeWet	orange	Peach Blossom	double deep rose
First Lady	reddish-violet	Preludium	salmon, white base
Garden Party	white-edged red	Queen of Sheba	mahogany orange
Gudoshnik	streaked yellow	Westpoint	yellow

David Trinklein, Department of Horticulture, UMC, (573) 882-9631