Documents: Special Interest: Seeds, Bulbs & Such:

Forcing Dutch Spring-Flowering Bulbs
by Art Drysdale
by Art Drysdale


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

October 18, 2015

Above, a pot of bulbs ready for forcing once the bulbs are covered by a light application of the potting medium; a rectangular container likewise ready for a covering of soil. Below, a group of forced bulbs including daffodils and crocus; and an ornamental swan filled with Spanish pinkbells.
Author photos.



Over the past few weeks, I've read and heard a lot about how to "force" spring-flowering Dutch bulbs into bloom indoors. Much of that information contained false or misleading statements so I thought I should try to set the record straight from my point of view--i.e. having done hundreds of bulbs almost annually for over three decades!

Forcing Dutch Spring-flowering bulbs has become a popular pastime for folks anxious to see spring colour months before a long winter is over. Forcing means encouraging bulbs that normally bloom outdoors in the spring, to bloom indoors during the winter. In a sense, we trick the bulbs into blooming earlier than their regular season. The technique itself is simple and al-most any type of bulb--narcissus, daffodil, tulip, crocus, Dutch iris can be forced.

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 height 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 Canadian sphagnum peat moss or horticultural vermiculite, and one third sand.

An additional twist to planting bulbs for forcing (that has only 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 (if different types of bulbs are used), or a mix of colours (if different cultivars of the same type of bulb are used). It also allows you the bulb forcer to be ever so clever in your combination of bulbs and cultivars. It's always best to write down just what bulbs are in each pot, and to note the results the following spring, for future planting.

When you purchase your bulbs at your favourite garden centre be sure to buy good labels and a marker pen. 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 fine. 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, or you could use my method: in an old operating refrigerator. The old traditional trench in an out-side 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 is also still highly recommended.

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 don't know when to re-move the bulbs from the cold storage.

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 conditions, and 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. There are a few simple tests you should do to see if your forced bulbs are ready or not, once they've been in the cold for nine weeks.

First check the roots. 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 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 and, sup-porting the potting medium with one hand, gently remove the pot 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 at the cool temperature.

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 at 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 when brought in. Although this in itself does no harm, care should be taken not to touch the growth sprouts until they have thawed out. At this early stage, breakage of the bulb’s stem is easily possible. Be careful!


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