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THE CHILLING FACTS
ABOUT FORCING FLOWER BULBS
"Forcing" — coaxing, actually — is the term used to
describe the process that stimulates bulbs to bloom out of season. Among the
most commonly forced bulb flowers are amaryllis, paper-white narcissus, muscari
and hyacinths. Certainly they are the easiest. However, other bulbs that can be
forced include colchicum and miniature iris. When selecting bulbs for forcing,
look for varieties that are specifically recommended.
Spring flowering bulbs usually require a rooting period of about 12 to 15
weeks at temperatures between 41-48°F in order to produce a good root system,
which is essential if they are to be "forced" into flower.
In this article:
SEE ALSO:
Storing Bulbs
Bare bulbs can be stored for several weeks in your refrigerator prior to potting
without damage if they are packed properly. However, they will still require a
rooting period after they have been potted.
The best way to store them is in a mesh bag or paper bag with holes that
permit ventilation. You don't have to worry about water, as the humidity inside
a refrigerator is usually high enough. Check them periodically to make sure they
are not molding or drying out.
Pot your bulbs right away if you have an appropriate location immediately
available, such as an old (functioning) refrigerator, a root cellar or cool
basement — or if outdoor temperatures are below 45°F. If, however, your area
experiences an "Indian Summer," your fridge can serve as a suitable
rooting area. Vegetable or crisper drawers can be used, but don't store bulbs in
the same drawer you keep ripening fruit or vegetables which give off ethylene
gas which can harm the bulbs. (Also some bulbs are poisonous, so this storage
method is not recommended for households with young children.)
Use clean pots with drainage holes (the depth will depend on the bulbs being
grown). Allow for 2 inches of soil below the bulb and select a pot large enough
to allow the top of the bulb to be even with the rim when placed on the soil.
Plain potting soil is fine. You can add some bone meal or special fertilizer
formulated for bulbs, just a "pinch" per bulb, to the soil mixture.
Place 2 inches of soil in the pot, then place (don't push) bulbs into
position. Add enough soil to fill the pot, firming the soil gently around the
bulbs being careful not to bruise them. Water well in order to settle the soil
around the bulbs. Bulbs can be planted very close together, even touching, and
make the best show in "crowded" arrangements.
Different types of bulbs require differing periods of time to root well. For
this reason it is not advisable to combine different types of bulbs in the same
pot. Label each pot with the name of the variety, planting date, and the date
you intend to bring it out of storage for forcing.
Bulbs will flower some 3-4 weeks after they have been brought into warmer
temperatures. Thus, from time of planting to flowering, allow a period of 15
weeks, comprised of 12 weeks for rooting, 3 weeks in warmer temperatures to
flower. (It is easier to hold bulbs back than to speed them up, so when you know
the date you want them to be in flower, calculate accordingly the best planting
time. (For Valentine's Day flowers, for example, plant bulbs in early- to
mid-October).
The following timetable will help plan a forcing schedule in order to have
bulbs in flower at a given date. Remember that these can vary, and in all cases,
the bulbs must be well rooted before being forced.
- 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
There are exceptions: amaryllis and Paperwhite narcissus.
Outdoor Garden Forcing in Cool-Moderate Climates:
An outdoor garden or any location or structure where temperatures can be kept
at 35-55F can be used to store potted bulbs for rooting. An unheated basement or
cool, ventilated crawl space is often the most convenient.
Potted bulbs can be placed outdoors for rooting if you live in an area where
the outside temperature cools off to the 40°F range. In areas where the winter
temperatures are likely to drop below 32°F, pots can be kept cool in a trench
in the garden or in a cold frame structure, but it's important to keep pots from
freezing.
A frame should be shaded and well drained. After pots are placed in the
frame, cover them with insulating materials, such as straw, if temperatures drop
below 30F.
If you choose a trench, select a sloping location (for better drainage). Mark
off and dig a trench about six inches wider than the pots. Spread an inch of
gravel or cinders on the bottom for drainage and set pots in. Place the pots in
the reverse order in which you will remove them. Cover pots with a soft,
non-compacting material such as vermiculite. Add hay, fir bark or peat moss
after the first frost.
Indoor Forcing Southern and Hotter Climates:
There is no reason why apartment dwellers should be deprived of the enjoyment
of growing and enjoying flowers. Those living in warmer climates where the
outdoor temperatures do not get low enough for good rooting can follow the same
procedures.
After potting the bulbs, place pots in the vegetable section of the
refrigerator where they receive the required rooting temperature. The length of
time will be the same, between 12 and 16 weeks.
The actual forcing begins at the stage when you remove the bulbs from the
root-growing environment into warmth and light, triggering the growth of leaves
and flowers. Sunshine and temperature are the most important factors in
promoting successful flowering. Most bulbs will require about 3 or 4 weeks from
the time they are removed from cold storage before they bloom.
After the rooting period specified for your particular bulb variety
(generally at least 12-14 weeks), transfer the pots to a place indoors with
indirect sunlight and temperatures about 60°F for a week or two.
When the shoots are 4-6 inches tall, move the pots to a bright, sunny window
to stimulate blooming. A temperature of about 68°F and direct sunlight will
produce the best results. When the buds take on color, return the plants to
indirect sunlight to make the blossoms last. Keep the soil moist at all times.
If blossoms begin to develop too quickly, you may be able to retard blooming
a bit by moving the pots out of direct sunlight and into a cooler location.
Re-acclimate them to sunlight and warmer temperatures when you want them to
resume growing.
After blooming, hardy bulbs such as hyacinths and tulips cannot be forced
again and should be discarded. Or they can be planted outdoors where they may
rebloom within a year or two. There is an exception. . . .
Unlike most other bulbs, amaryllis bulbs will bloom again and again, provided
they are properly cared for. After the bulb finishes blooming, cut off the
flower stalk close to the base. Keep the plant moist and add house plant
fertilizer regularly (a leafy amaryllis makes an attractive house plant even
without blooms). Stop watering and feeding in August/September, and allow the
plant to dry out completely in the sun. In early fall, remove and clean the
bulbs of old scales and dead foliage. Roots should be fleshy and not damaged.
Re-pot in a clean container with the neck of the bulb above the soil, water
and place in a cool, sunny spot. Water sparingly until the first sprout appears,
then keep moist. In about eight weeks the bulb will bloom again.
Paperwhites (narcissus tazetta), 'Soleil d'Or', 'Chinese sacred lily'
and colchicum are among the most popular forcing flowers that don't require the
12-week rooting period. They are easy to start and can give you indoor blooms
from Thanksgiving until late March, if planted successively, batch after batch
in late fall.
Paperwhites are most often (and most easily) potted in shallow containers of
gravel. Place bulbs on a layer of gravel and carefully fill in enough gravel to
hold bulbs but not cover them. A crowded grouping will be the most attractive.
Add water to the container. It should go just to the base of the bulbs, but
not touching the bulbs. Place container in a sunny spot, step back and watch 'em
grow! You'll see roots in a day or so and in three to five weeks you'll have
gorgeous flowers.
- Paperwhite narcissus; popular bulb; grows in soil or
gravel
- amaryllis; popular Christmas plant (plant bulb in early
November, no cooling necessary)
- large-flowering crocus; requires 12-14 week rooting
period; bulbs can be potted in gravel and water for different effect
- hyacinth; fragrant spring-time favorite; requires about
12 weeks for rooting; can be forced in special "hyacinth" vases
using only water
- colchicum; excellent for forcing, can even grow on a
window sill without soil or water; begins blooming in about two weeks
- muscari; requires 16 week rooting time; pot plenty,
they're small
- iris; especially iris reticulata are easy to force, but
need careful attention to drainage; require about 15 weeks for rooting;
don't hold iris bulbs too long before potting; tall-stemmed iris are less
suited to forcing
Forced tulips do not do quite as well as garden planted tulips because they
require a fairly long rooting period at even (non-fluctuating) temperatures
to be successful. Allow at least 15 weeks.
Experiment with a few pots of different varieties. One to try is the
distinctive 'Princess Irene'. This single early tulip is orange with purple
flame markings. The bright yellow 'Monte Carlo' is a double early tulip, a
cultivar that has twice as many petals as most tulips.
Tulip Tip: Plant bulbs with flat side facing the rim, this will position
the larger outer leaves toward the pot rim, where they will drape gracefully
over the edge of the pot.
Daffodils require very bright light, such as that found in a greenhouse,
to flower well. Too little sun results in leggy growth and no blossoms. Only
the miniature varieties (hybrid) daffodils are recommended for home forcing.
Daffodils usually require a 12-14 week rooting period.
Once removed from the rooting area, daffodils must be placed in a
location that receives lots of sun, say an enclosed porch or sun room or
under a skylight.
Lily-of-the-Valley are often pre-cooled when you buy them, so they will
bloom three to four weeks after planting. Ask your supplier.
Freesias don't require a cooling period, however they usually require a
lot of sunshine and about three months of growth time before they bloom.
These fragrant flowers do best in a very bright room with daytime
temperatures of about 70°F and nighttime temperatures of about 50°F.
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