Home Bulb Forcing

Introduction

Most people like to receive bulbs as gifts at the planting stage so they can watch the bulbs grow and flower. Amaryllis and paper-white narcissuses can easily be brought into flower in time for the winter holidays if you start about 6 weeks in advance. For those who want their flowers to open right away, give the bulbs as gifts just before they start to open. Spring bulbs such as crocuses, daffodils, hyacinths, and tulips can also be given for spring holidays, such as Saint Valentine’s Day, Mother’s Day, or as spring wedding gifts, but these bulbs do require more planning.

Forcing is causing bulbs to flower in other than naturally occurring conditions. Basically, there are only two types of bulbs for forcing indoors: those that need a cold period and those that don’t. Typically, crocuses, daffodils, hyacinths, and tulips are the most popular, but other spring flowering bulbs such as bulbous irises, English bluebells, glory-of-the-snows, grape hyacinths, and snowdrops may also be forced using similar procedures. These bulbs require a cold period and are typically forced into flower for late winter and early spring, January through April. Paper-white narcissus and amaryllis bulbs offer more flexible forcing, because, unlike the bulbs previously mentioned, they do not require a cold period to flower.

History

In the 1600s, fresh flowers made their way into the homes of the prosperous across Europe and were perceived as luxury items. For those without the means to display fresh flowers for any occasion, artificial flowers became popular. Finally, indoor bulb cultivation began so that people of modest incomes could have flowers at any time of the year using a few simple forcing guidelines.

What Is a Bulb?

When gardeners use the word bulb, they generally refer to plants that grow from underground structures such as corms (e.g., crocuses and gladioli), rhizomes (e.g., canna lilies and irises), true bulbs (e.g., tulips and daffodils), tubers (e.g., caladiums and gloriosa lilies), or tuberous roots (e.g., dahlias and sweetpotatoes). However, all bulbs share a characteristic separating them from other flowering plants—a self-contained, underground, food storage tissue able to nourish the plant during harsh environmental conditions, such as the cold of winter or the heat and drought of summer. These storage tissues accumulate food stores, such as sugars and starches, from the leaves in the period of time after flowering in preparation for the next growing season. Therefore, the bulb will be ill-prepared for dormancy if the novice bulb gardener (either indoors or outdoors) cuts the leaves off soon after the bulb has finished flowering.

Purchasing Bulbs

When shopping for bulbs in a local garden center, imagine selecting onions in the grocery store. Begin with healthy, undamaged bulbs that are firm to the touch, are free of mold or dark, bruised spots, and are the correct size for that type of bulb. Pass over bulbs with blemishes, that feel soft, or are an unusual shape or size. Bulbs contain the food for upcoming flowering, so purchase only high quality bulbs. Of course, you do not have the opportunity to judge bulb quality when ordering by mail. However, suppliers who specialize in bulbs and carry a large selection may more reliably offer quality bulbs. Some bulbs are also sold in grades based on bulb diameter. In general, larger bulbs yield larger plants with more flowers.

Keep in mind when shopping for bulbs to grow indoors that some require a cold period and others do not. Some companies may also label bulbs as prechilled or precooled, meaning they have already received a cold period and will grow and bloom in about 2 to 3 weeks. If you purchase precooled bulbs and cannot plant them right away, protect the bulbs from temperatures greater than 70 degrees F. High temperature effectively erases the bulb’s memory of prior cooling, which causes poor flowering.

Once purchased, store bulbs in mesh or paper bags (not plastic) or in any container that allows good air circulation and place them in a cool, dry place until you are ready to plant. A dry, cool basement or garage is ideal; bulbs can even be stored in the refrigerator. In a refrigerator, you don’t have to worry about bulbs drying out because the relative humidity inside is usually high enough. Check them periodically for molding. Also do not store them with any fruit. Ripening fruit gives off ethylene gas, causing the bulbs to produce distorted growth and no flowers. Tulips are particularly susceptible. Do not expose unplanted bulbs to freezing temperatures either in a freezer or outdoors.

Scheduling

• To flower in January, plant in September or very early October.

• To flower in February, plant early to mid-October.

• To flower later, plant in late October or early November.

Planting

NOTE OF CAUTION: Hyacinth bulbs contain oxalic acid that can cause skin irritation. Before planting, thoroughly rinse the bulbs with water to reduce the potential for skin irritation and wear gloves for protection.

The potting mix for bulbs should be a sterile, soilless, well-drained mix that can be purchased at garden centers or mass market stores in plastic bags. Look for a light-weight mix often labeled professional potting mix. Fill the container about half full with potting mix, set the bulbs so their tips are at or just above the container rim, and fill in around the bulbs with potting mix, firming the mix lightly as you go to about ¼ inch below the container rim. Pushing bulbs into the potting mix may compact the soil below the bulbs or damage the bulb base and inhibit rooting. Do not add fertilizer at planting time.

Plant flat-sided bulbs, such as tulips, with the flat side facing the inside of the container. This allows the first leaves to emerge facing outward to form an attractive border around the margin of the pot. For a striking mixed container, place a second set of smaller bulbs of a different type in between the first layer of large bulbs by loosely spacing the first layer. Put the second layer in place, then sift in more potting mix, firming the mix as you go. For example, crocuses or grape hyacinths can be planted among tulips or daffodils.

Water the container thoroughly after planting. Apply water from overhead or partially submerge the containers in a pan of water until the potting mix surface is wet. Write the name of the bulb cultivar on a plastic label and, if the bulbs require a cold period, the date the bulbs were placed into the cold period and the date they should be removed from the cold period. The plastic label helps you determine how much time you have left before removing the containers from the refrigerator to grow them. For cold requiring bulbs, keep in mind the potting mix must be kept moist during the cold period and you must not store bulbs with fruit.

Hyacinths can be grown in water with the base of the bulb just above the water. This is done using hourglassshaped vases known as hyacinth glasses. Their design allows the bulb to sit just above the water without the water touching the base of the bulb. Because hyacinths require a cold period, place them in a refrigerator for roots to form and the bulb to sprout. Don’t forget to maintain the vase water level.

Cold Period

Finding the right place to provide a cold period for your bulbs is the real challenge. Suitable locations for providing a natural cold period could be an unheated basement, storage area, garage, or cold frame. If you live where outdoor winter temperatures rarely get below 25 degrees F, just keep the containers of bulbs moist and store them right in the garden beneath a layer of straw mulch. However, protect the bulbs from freezing and keep the potting mix moist during the cold period. Using a natural cold period is fine for forcing bulbs into flower in the spring, but the southeastern United States does not have cold temperatures early enough for forcing bulbs into flower during the Thanksgiving and Christmas holiday period. A refrigerator may be used for this or any target flowering period during the year. Some people may object to having dirty containers of bulbs in the same refrigerator with food or serious bulb gardeners may not have enough room for their ambitions; purchase a used refrigerator just for bulb forcing purposes. Obtain as many shelves as possible to accommodate as many containers as you desire.

If the bulbs must receive a cold period in a refrigerator containing food, especially fruit, place the containers in zippered plastic bags to protect them from ethylene gas and to help keep the refrigerator clean. At least once a month, open the plastic bags for and hour or two to allow fresh air exchange and to check watering needs. Reseal the bags and place them back in the refrigerator. After the period specified in Table 1, roots should be visible through the drainage holes and short, yellow shoots should have emerged from the bulbs. Bring the containers out into a medium-light, cool room at 55 to 60 degrees F for 4 or 5 days, then move them into a bright window with normal room temperatures. Keep the bulbs well watered and they will flower in about 2 to 3 weeks. Once the flowers open, the bulbs can be moved to a cool location at night to extend the flowering period. For a succession of flowers through the winter, bulbs can be planted and removed from the cold period every 2 weeks with planning.

Forcing

Amaryllis

When planting amaryllis bulbs, do not crowd them in the container. Plant with no less than an 1 inch of space around the bulb and with one-third of the bulb above the container rim. Because the flower stalks are so tall and the flowers so large, plant them in a container with a wide enough base to provide stability. Water the container thoroughly and place it in a warm spot (70 to 75 degrees F) out of the sunlight. Don’t overwater. Initially, watering once per week is usually adequate. Avoid watering over the bulb tip. When the first sprouts appear in about 2 weeks, water them more often and place them in as bright a window as possible, but avoid direct sunlight. After the bulb begins to grow, fertilization is essential. Use either a complete N-P-K liquid fertilizer two to four times per month or a slow-release fertilizer that lasts several months. Follow the fertilizer package recommendations. In a window, the tall flower stalks will naturally grow towards the light; so it is a good idea to rotate the container every couple of days to keep the stems straight. Amaryllis can be grown outdoors in USD A Plant Hardiness Zones 8 to 10. Therefore, if they will not be reflowered indoors, plant the bulbs in the garden after the danger of frost has passed.

Unlike most other bulbs, amaryllis bulbs will flower again and again with proper care. Amaryllis bulbs that have retained their original bulb size or have increased in size can be reflowered. After flowers fade, cut off the flower stalk close to the base of the shoot and keep the potting mix moist. The key to reflowering is to place the bulb at a temperature of 55 degrees F for 8 to 10 weeks and stop fertilizing. Withhold water and place the bulb in a cool storage area (no light) or, preferably, place the bulb in a 55 degree F growing location (with light) for this length of time. It is not necessary for the plant to go dormant. Once the bulb has received 8 to 10 weeks of 55 degrees F, resume watering and force the bulbs at 70 to 75 degrees F as before.

If the amaryllis bulbs have been grown for 2 or more years, most cultivars will produce offsets or daughter bulbs at the base of the mother bulb. Offsets can be established on their own in one of two ways. First, the mother bulb can be transplanted to a larger pot with the offsets left attached. By doing this, a large number of flowering bulbs will ultimately be growing in a single pot. This creates quite a show. Alternatively, the offsets can be carefully removed from the mother bulb and each of them planted in individual pots. This should be done after the bulb has been stored cool and dry for 8 to 10 weeks. Remember that small offsets need to grow to a larger size to be able to flower, which can take a year or two.

Daffodils, Hyacinths, and Tulips

Table 2. Daffodil Cultivars for Home Forcing

Cultivars for January and February flowering
Yellow	Bicolor	White	Double
‘Carlton’	‘Barrett Browning’	‘Cassata’	‘Bridal Crown’
‘Dutch Master’	‘Fortune’	‘Mt. Hood’	‘Repleat’
‘February Gold’	‘Jack Snipe’	‘Ice Follies’
‘Peeping Tom’	‘Juanito’	‘Printal’
‘Tête a Tête’	‘Las Vegas’
‘Unsurpassable’
Cultivars for March and April flowering
Yellow	Bicolor	White	Double
‘Dutch Master’	'Accent’	‘Cassata’	‘Bridal Crown’
‘Osiris’	‘Barrett Browning’	‘Mt. Hood’	‘Repleat’
‘Prizewinner’	‘Bridal Crown’	‘Ice Follies’
‘Unsurpassable’	‘Flower Record’	‘Printal’
	‘Fortune’
	‘Las Vegas’
	‘Magnet’
	‘Jack Snipe’
	‘Salome’
	‘Jules Verne’

Table 3. Hyacinth Cultivars for Home Forcing

Flower color	Cultivar	January	February	March	April
Blue	‘Atlantic’*	X	X	X
	‘Blue Jacket’*		X	X	X
	‘Blue Star’*		X	X	X
	‘Delft Blue’	X	X	X
	‘Ostara’*	X	X	X
Pink	‘Anna Marie’*	X	X	X
	‘Lady Derby’		X	X	X
	‘Marconi’*			X	X
	‘Pink Pearl’*	X	X	X	X
	‘Pink Surprise’*		X	X	X
Light pink	‘Champagne’		X	X	X
Red rose	‘Amsterdam’*	X	X	X	X
	‘Jan Bos’	X	X
Violet	‘Amethyst’*			X	X
	‘Anna Liza’		X	X
White	‘Carnegie’*		X	X	X
	‘L’Innocence’	X	X
	‘Polar Giant’*		X	X	X
	‘White Pearl’*		X	X	X
Yellow	‘Yellow Queen’		X	X	X
* Suitable in 4-inch pots

Table 4. Tulip Cultivars for Home Forcing

Cultivars for January and February flowering
Cultivar	Color	Cultivar	Color
‘Abba’	red	‘Merry Christmas’	red
‘Abba’	dark red	‘Monsella’	yellow with red
‘All Seasons’	cherry red	‘Monte Carlo’	lemon yellow
‘Arie Hoek’	red	‘Montreux’	yellow blush pink
‘Bastogne’	red	‘Negrita’	deep purple
‘Blenda’	carmine red	‘Orange Cassini’	orange
‘Carola’	dark pink	‘Orange Monarch’	orange
‘Cassini’	dark red	‘Peach Blossom’	carmine pink
‘Christmas Dream’	rosy red	‘Purple Prince’	purple
‘Flair’	red	‘Recreado’	magenta
‘Hollandia’	vermilion	‘Red Paradise’	vermilion
‘Kareol’	dark yellow	‘Rosario’	rose
‘Kees Nelis’	red edged yellow	‘Stockholm’	scarlet yellow
‘Leen van der Mark’	red edged white	‘Viking’	red
‘Leo Visser’	red edged white	‘White Dream’	ivory white
‘Libretto’	rose	‘Yellow Present’	creamy yellow
Cultivars for March and April flowering
Cultivar	Color	Cultivar	Color
‘Angelique’	blush pink	‘Peach Blossom’	pink
‘Annie Schilder’	rosy orange	‘Pinocchio’	scarlet edged white
‘Arabian Mystery’	purple edged white	‘Plaisir’	red edged yellow
‘Arma’	red	‘Princess Victoria’	red edged white
‘Barcelona’	red edged carmine	‘Princess Irene’	orange with purple
‘Couleur Cardinal’	violet red	‘Red Present’	dark red
‘Debutante’	red edged white	‘Red Riding Hood’	red edged yellow
‘Esther’	fuchsia pink	‘Rococo’	red edged fire red
‘Friso’	red	‘Sevilla’	red
‘Globe’	dark pink	‘Topwhite’	white
‘Madison Garden’	carmine edged pink	‘Upstar’	white edged purple
‘Oscar’	red	‘Van Eijk’	Salmon
‘Page Polka’	red striped white	‘Wirosa’	pink edged white
‘Passionale’	purple	‘Yellow Flight’	yellow

Planting all three bulb types can take place any time from mid-September through December, depending on the desired date of flowering. As a general rule, plant early for early flowering dates and plant late for late flowering dates. For flowering in late December, the planting must be planted in mid-September; for February flowering, the bulbs should be planted in mid-October; and for March and April, plant in mid-November. Remember, the minimum length of the total cold period is 13 weeks and 15 weeks is preferred for daffodils. The minimum length of the total cold period is 10 to 13 weeks for hyacinths. Longer times result in taller plants and shorter times result in smaller plants that may not flower. Cold period times for tulips vary by cultivar; therefore, exact cold period times must be obtained from the bulb supplier.

The first containers may be placed in the home after the minimum cold period. For a continuous supply of flowers, bring out a few containers at weekly intervals. In the house, place the containers in an area with a temperature of approximately 63 degrees F and, for best results, place them in direct sunlight. Once the flowers begin to open, they will last longer if the containers are placed out of direct sunlight. Because the bulbs contain enough stored food reserves, it is not necessary to fertilize them.

Paper-white Narcissuses

Initially, place the containers in an area at 60 to 65 degrees F. Then move them to normal room temperatures when flowers begin to open. Paper-white narcissuses will flower under any light conditions but, for best results, initially place them in a window with a bright southern exposure, then move them to lower light to help prolong flowering. Paper-white narcissuses can be grown outdoors in USD A Plant Hardiness Zones 8 to 10. Therefore, if they will not be reflowered indoors, plant the bulbs in the garden after the danger of frost has passed.

Other Easy Bulbs

• Large-flowering Dutch crocuses require 12 to 14 weeks of cold followed by 2 to 3 weeks of forcing. The bulbs look best when planted close together in a shallow container. They can also be potted in gravel and water for a different effect.

• Autumn crocuses are excellent for forcing in the fall because they do not require a cold period and will flower about 2 weeks after potting. In fact, it is difficult to keep them from growing even when unpotted.

• Grape hyacinths require 14 to 15 weeks of cold followed by 2 to 3 weeks of forcing. Purchase and pot plenty of bulbs. They’re small, inexpensive, and look best when planted close together.

• Dutch bulbous irises are easy to force, but need excellent drainage and the bulbs do not keep long before potting. They require 12 to 14 weeks of cold followed by 2 to 3 weeks of forcing.

After the Blooms Fade

Colleen J. McGrath, Graduate Associate, and J. Raymond Kessler, Extension Horticulturist, Associate Professor, both at Auburn University.

For more information, contact your county Extension office. Visit http://www.aces.edu/counties or look in your telephone directory under your county's name to find contact information. Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability.