Documents: Special Interest: Seeds, Bulbs & Such:

Forcing Spring-flowering Bulbs for Bloom Indoors
by Art Drysdale
by Art Drysdale

email: art@artdrysdale.com

Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at http://www.artdrysdale.com


October 14, 2012

Above, a group of mixed bulbs in a pot ready to be covered with more soil, and put away for cooling, photo by George Weigel. Below, ten tulip bulbs in a clay container ready to be planted in a soil medium and put into an old refrigerator for about 9 to 11 weeks, photo by Gardening-Guy.com.

Having written about planting bulbs, albeit fall-blooming ones, last week, I was reminded that I had not written about the forcing of spring-flowering bulbs for some years. When I checked the ICanGarden.com site, I noted that I had written lengthy items on this topic back in 1998 and then again in 2000 and 2002, but not much since. Other writers on the site too have written on this topic, but most not to the depth I had in the past.

Forcing means encouraging bulbs that normally bloom outdoors in the spring, to bloom indoors during the win-ter. The technique itself is simple and almost any type of bulb--narcissus, daffodil, tulip, crocus, etc. can be forced. The early-flowering types are best suited for forcing, but there are exceptions to that ‘rule’ as well.

Since little horticultural skill is required, it is an excellent project for beginning gardeners and now is the perfect time to start. The sooner you start, the sooner you will have bulbs in full bloom in your home. Bulbs to be forced should be planted in plastic or clay pots with at least one drainage hole. The pots need not be deep, in fact they need only be just slightly deeper than the depth of the bulbs to be planted; such pots are often referred to in the trade as bulb pans. As far as planting soil, it should be a light, sandy soil, with plenty of humus such as peat moss added. If you are going to mix some, a good mixture is one-third soil from your garden, one third sphagnum peat moss or horticultural vermiculite, and one third sand.

One additional twist to planting bulbs for forcing that has come along in recent years is to use deeper clay or plastic pots, instead of the pans, and actually plant two layers of bulbs--perhaps two different types of bulbs, or two different cultivars of the same type of bulb. This method of planting generally yields flowers over a much longer period of time. It also allows you the bulb forcer to be ever so clever in your combination of bulbs and cultivars.

For the best possible flowering, use as many bulbs as will fit into the pot without touching each other--a few millimetres apart is just great. With tulips specifically, place the bulbs at the outside edge of the pot with their flat side facing the pot. This will give a better look when the bulbs actually flower.

Bulbs should be planted so that they are just under the surface of the soil. They should then be watered well, leaving the pot to soak overnight, and then put into cold dark storage--in a cold (not freezing) basement or garage; in an old operating refrigerator; or, use the old traditional method. This involves placing the pots of bulbs into a trench in an outside garden, somewhere close to the foundation of the house, and with a good covering of shredded Styrofoam and/or leaves over the pots in the trench.

During this period of cold treatment, the only additional care needed is an occasional check to make sure the soil remains moist. Considering that the bulbs already contain an almost fully developed flower bud, it should be a simple task to get them to bloom when required. However, there is one step in forcing with which many folks have trouble: they simply don't know when to remove the bulbs from the cold storage and bring them into the daylight. First of all, it must be understood that there is no clear-cut period of time during which bulbs should be kept at cool temperatures. Everything depends on the exact conditions given, and also on the type of bulbs. In most cases, temperatures of about five to nine degrees Celsius will produce the fastest growth, while temperatures much higher or lower, will slow things down. In general, a 9-14 week period of cold is best.

There are a few simple tests you should make to see if your forced bulbs are ready once they've been in cold storage. First, check the root systems. Bulbs with only a few roots are not yet ready to bring out of the cold. They need an abundant supply of roots before they can support flowering. One possible sign that the bulbs are ready is when roots emerge from the drainage hole(s) at the bottom of the pot. However, an even more thorough check is recommended. Turn the pot upside down, support the potting medium with one hand and gently re-move it from the root ball. If the bulbs are ready, the entire inner surface of the pot should be covered in white roots and the growing medium should hold firmly together--anything less means that the bulbs need more time in the cold.

A second test is to study the top growth. Bulbs are generally ready to come out of cold storage when the sprouts appearing from their tops seem firm and well-developed. When you can feel the flower bud in the sprout above the bulb and the average cold requirement of 9 to 14 weeks of 9 degrees Celsius has been reached, it is time to place the bulb pots in the home where you wish them to bloom. A cool room--the cooler the better--and out of the sun is best. If the bulbs were stored outdoors, and the temperatures were very cold, the sprouts may be frozen. Although this does no harm, take care not to touch the growth sprouts until they have thawed.

When the bulbs you have been forcing, are ready to come out of storage, whether it be a spare refrigerator (my favourite way of forcing), or an outdoor pit, first, place the bulbs in the coolest spot possible--perhaps near a north facing window or in a cool basement--then gradually move them to a spot where night temperatures of about 15 C can be maintained. Although partial sun is sufficient, full sun will produce better plants. Once temperatures have been increased, your bulbs will be in flower within a very short time--between a few days and two weeks, depending on the type.

Watering should be maintained throughout all stages of forcing. Finally, if you decide to force a number of pots of bulbs, such as an old basement refrigerator will handle easily; remove the pots from the cold one or two at a time. That way, as few as five or six pots will give you colour throughout much of the winter. Some pots of bulbs, by the way, may require light staking and some string to keep the flowers upright. You shouldn't confine your forcing activities to just the well-known bulbs such as tulips and daffodils. Several years ago I experimented with a number of the more unusual bulbs such as Iris, and had excellent results. Another important point, once your forced bulbs have completed their flowering, it is best to discard them. However, daffodils naturalize well, especially under older trees and may be expected to bloom again in the second season following planting out.

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