How to: Force Bulbs


I don’t know about you, but I’ve had enough of the cold and brown outside!  When it gets to this point at the end of winter all I want is a little bit of color and to at least feel like Spring is on its way.  Forcing bulbs is perfect for not only the holiday season, but also for the last few months of Winter.  There are several different ways to force bulbs indoors including simply purchasing ones that are ready to go from your local plant center. Most commonly you’ll find amaryllis and paper whites at these places.    If you can’t find them or are interested in forcing different types of bulbs keep reading for my tips on tricking your bulbs into thinking it’s Spring!

The term forcing refers to inducing a plant to produce its shoot, leaf, and flower ahead of its natural schedule and out of its natural environment. To force hardy bulbs you need to mimic and compress the process the plant would undergo outdoors in the garden.

When buying bulbs for forcing, always choose first-rate, top-size varieties.  If you buy from the local garden center, scrutinize them the way you would produce at the grocery store; don’t buy bulbs that are soft or sprouting. High-quality bulbs are necessary because the bulb contains the food required to produce a flowering plant.

Since bulbs need moisture and perfect drainage, a mixture of equal parts peat moss, potting soil, sand and vermiculite or perlite is best. Mix thoroughly and moisten with enough water to a damp consistency. If you anticipate planting bulbs outdoors after forcing, add 1 teaspoon of 5–10–5 dry fertilizer to every quart of soil mix to give the bulbs an extra boost after flowering. Hyacinths, crocus, and narcissi can be grown in pebbles and water—with no additional nutrients, however, they are usually completely exhausted and should be disposed of after blooming.

The next step in planting is to place a few pieces of broken crockery over the drainage holes, to prevent the soil from running out initially and clogging later. Fill your pot half-full of soil mix, then adjust the soil level until the tops of the bulbs reach the rim of the container.

Plant bulbs with the pointed ends up, as close together as possible, without letting them touch. Tulip and other bulbs with a flat side should be planted with the flat side facing the edge of the container. This will allow the first leaves to form a border around the edge of the pot.

Add enough soil mix to fill the pot, and water the bulbs thoroughly from the top or immerse in a tub of water – this will settle the soil around the bulbs. Label each pot with the name of the cultivar, date of planting and date to bring out of cold storage.

After planting, place the pots in a cool, dark place, such as a cellar or refrigerator to initiate root and shoot growth. Other suitable environments include an insulated cold frame, under a porch, or an unheated garage. Cold storage is a critical step in the forcing process. Ideally, temperatures should be 35° to 48°F. If necessary, set boxes, pots or black garbage bags over your potted bulbs to keep them dark during the cooling period. The medium should be kept moist through the rooting and cooling period. After five or six weeks, the roots should emerge out of the bottom of the containers of the large hardy bulbs.

Forcing will take about 12 weeks for the early blooming bulbs (snowdrop, crocus, daffodil) and about 16 weeks for the tulips. Longer cold storage will result in taller flowers, while storage time shorter than 13 weeks will result in smaller plants and sometimes aborted flowers. A good rule of thumb: when you see the shoots 2 to 3 inches above the soil and fine white roots emerging from the drainage holes, it’s time to bring the pots out of cold storage. At this stage of development, move the bulbs to a cool location, such as an unheated entryway or closed off back bedroom, where the temperatures are in the ’50s. Bulbs should be placed in indirect lighting and should not be allowed to dry out.

Feed weekly with a half-strength solution of houseplant fertilizer. Turning the pots every day or so keeps the flower stems straight and strong. In a week or two, the stems will elongate and the buds will become plump. When the foliage and buds are well developed, move the pots to a bright, sunny window in the house, where temperatures are near 65°F. Once the flowers begin to open, take the plants out of direct sunlight to prolong the bloom.

You will be pleased at how quickly the bloom unfolds compared to weeks, or possibly months, before they would outside. Hyacinths will bloom for nearly two wonderfully fragrant weeks if the room is between 65° to 68°F. Iris reticulate and crocus may fail to bloom or last only a day if temperatures get over 65°F.

After flowering, cut the flower stems and place the pots in direct sunlight, keeping the foliage growing until it begins to die back. As it withers, don’t pull the leaves off, store the bulbs in the pots in a cool, dry place until late summer or early fall, at which time they can be planted into the garden. Attempts to force the same bulbs indoors will be unsuccessful, as forcing weakens the bulb and the bloom will be small and unsatisfactory the following year. Once the bulbs are back in the garden setting, they will return to a natural schedule, and in several years will again produce a wonderful show of flowers.

Happy Gardening!



1 Comment

Filed under Gardening, How To

One response to “How to: Force Bulbs

  1. Pingback: After-Bloom Care for Amaryllis Bulbs «

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