The Daily Southerner, Tarboro, NC

January 4, 2013

Ask A Master Gardener

FOR THE DAILY SOUTHERNER
Submitted

TARBORO — Candis O. (Tarboro) Asks: … This Christmas, I received forced bulbs that bloomed during the holidays. After they’ve been forced indoors in the winter, can they be planted outdoors in the spring?

Answer: If you receive potted, forced, spring-flowering bulbs, like daffodils and tulips, as holiday gifts, you may be tempted to plant them in the garden in spring. However, it often takes two to three years for bulbs to re-bloom after they have been "forced" for indoor use. Before starting, consider whether it's worth the effort.

If you want to try, start by keeping the plants actively growing until the leaves mature and die back naturally. To prevent seeds from forming, remove the flowers after they bloom. Place the potted plants in a cool, very sunny location and keep the soil moist to the touch. Fertilize with a water-soluble houseplant fertilizer according to label directions. The longer the leaves stay green and healthy, the larger the bulb will become. This improves its chances for blooming the following year.

When leaves dry down, store the bulbs in a dark, cool place until fall planting time. Because few homes have a good storage place, it may be better to directly plant the bulbs outdoors. If the leaves have died back, plant bulbs outdoors when the soil is workable. If the leaves have not died back, wait until after the last frost to plant the bulbs with their leaves.

Care for the bulbs outdoors as you would other spring bulbs. With luck, they'll bloom again -- eventually.

Marianne R. (Tarboro) Asks: Please explain the process of forcing bulbs.

Answer: Inducing bulbs to bloom when you want them to, rather than when they normally do, is known as forcing. In late summer, most bulbs are dormant with little if any active root growth and no shoot growth. As soil temperatures cool, the bulbs begin root growth, which continues until the temperatures become very cold. Shoot growth begins in the spring as temperatures begin to rise, and is followed soon after by flowering. After bloom, foliage continues photosynthesis and replenishes food stores in the bulbs. As foliage begins to die back, the bulb returns to a dormant state and the cycle is ready to begin again. Forcing is simply manipulating this cycle.

Most spring-blooming bulbs can be forced into bloom. The most common choices are hyacinths, tulips, narcissus, grape hyacinths and crocuses. Catalogs and garden center displays often indicate which cultivars and types of bulbs are more suitable for forcing. Choose only top size bulbs for best blooms.

Almost any container can be used for forcing bulbs. Specially designed vases for forcing individual hyacinth bulbs are available. Paperwhite narcissus can be easily forced in a shallow container of water using pebbles for support. More extensive forcing projects are best done in clay or plastic pots that have adequate drainage holes.

The best soil mix for forcing bulbs contains equal parts of soil, spaghnum moss, and perlite or vermiculite. Commercial "soil-less" potting mixes can also be used. Bulbs for forcing should not be planted in ordinary garden soil or in potting mixes that are labeled "potting soil." Potting soil mixes are often no more than a fine form of peat moss. This type of material holds too much moisture and may cause water-related disease problems.

Planting - Fill three-quarters of the container with potting mix. Plant bulbs closely together. Spacing considerations that apply to planting bulbs in the garden do not apply when the bulbs are to be forced. Place tulip bulbs with the "flat" side facing the edge of the container. After you arrange the bulbs, place additional media around them. Do not fill the container to the surface with the potting mix. The tops of tulip and narcissus bulbs do not need to be covered. The bulbs should then be watered in.

Cold period - All of the spring-blooming bulbs, with the exception of paperwhite narcissus, must have a cold period of at least three months to initiate bloom. You can supply this cold period in a variety of ways. Potted bulbs can be stored in a refrigerator or in an unheated garage or cellar. Pots in a refrigerator tend to dry out rapidly; check periodically to ensure that the soil is moist.

Forcing - After bulbs have been chilled, bring the pots inside for blooming. Check the pots to see if the bulbs have produced an adequate root system (look to see if any roots are visible through the drainage holes). The number of weeks it takes before the plants actually bloom depends on the environmental factors in the home, but the average is two to three weeks.

Water the pots thoroughly when bringing them inside. Place pots in a cool area of the home (high light intensity is not important at this point) and leave pots in a cool location until active growth is visible. Take care not to over-water. Once active growth begins, you can move the pots to a warmer location that receives more light. Forcing bulbs slowly is more desirable than placing them directly in a bright, warm location. The quick transition from chilling to warm temperatures can sometimes "blast" the buds, which means everything moves too fast and the bulbs do not bloom. Because of the warmer indoor temperatures, flowers from bulbs that are forced indoors do not last as long as outdoor flowers. Forcing several containers of bulbs on a staggered schedule extends the indoor display.



“Ask A Master Gardener” is a weekly column providing our readers solutions to common problems concerning horticulture, gardening, and pest management.  Trained Extension Master Gardener Volunteers have access to the research that provide answers.  

Submit your questions by email to askemgv@gmail.com.  Or call the local Extension Center at 252-641-7815 and tell them you have a question for a master gardener; a volunteer will return your call with a solution to your problem, or write to “Ask A Master Gardener”, c/o The Daily Southerner, P.O. Box 1199, Tarboro, NC 27886.