Forcing Bulbs to Bloom Indoors

Copyright © 2011 by McGroarty Enterprises Inc.

Beautiful blooming tulips, daffodils and other flowering bulbs are always a welcome and refreshing sign of spring. But you don’t have to wait until warm weather arrives to begin enjoying these lovely and aromatic spring flowers. In the dead of winter when spring fever hits, you can enjoy a preview of spring by forcing bulbs to bloom indoors.

Although forcing bulbs may seem like a mysterious and difficult project, it really isn’t, but it does require some forethought. It may be difficult to find the bulbs you want in November, so bulbs should be purchased in the early fall while they are readily available for planting outdoors.

Just about any spring bulbs can be forced to bloom indoors ahead of their normal schedule, but some will perform better than others. Generally, bulbs that are best for forcing will be labeled as such at the garden center or in catalogs that offer bulbs. The most common forcing bulbs are tulips, narcissus, crocuses, paperwhites and hyacinths, along with some varieties of irises. For the best display, always choose healthy, top size bulbs that are free from blemishes. Avoid purchasing bulbs that have already begun to sprout.

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When forcing bulbs, the planting container should provide good drainage, so drainage holes in the bottom are absolutely necessary. The container can be plastic, ceramic or terra cotta, or you can be creative and use containers that aren’t normally meant for planting, so long as the container has drainage holes. Small bulbs, such as crocuses or grape hyacinths can be planted in shallow dishes, while larger bulbs will need a deeper pot that will contain their larger root systems.

The choice of potting mix is more important than the container type when forcing bulbs. The potting mix must hold moisture adequately while also allowing for sufficient drainage. A commercial soilless mix may be used, or find a mix that contains equal parts potting soil, sphagnum or peat moss and vermiculite or perlite. Garden soil or 100% potting soil should not be used as these will hold too much moisture.

Next, fill the container about three-quarters full with the potting mix. When forcing bulbs, the rules for placement of the bulbs will not be the same as when planting them outdoors. The bulbs will produce a prettier display if they are planted closely together, but not quite touching each other. If any of the bulbs have a flat side to them, as tulip bulbs often do, situate the bulbs so the flat side is facing a side of the container. When those bulbs produce their first leaves, the leaves will form a border around the inside edge of the container.

While bulbs that are planted outdoors are generally planted at a depth about three times the size of the bulbs, the rules change when forcing bulbs to bloom indoors. The tops of narcissus and tulip bulbs do not have to be fully covered with potting mix and may be allowed to peek out from above the potting medium. However, planting them a bit more deeply won’t hurt either. Once all the bulbs are arranged in the container, add additional potting mix around them, then water it well to settle the soil around the bulbs.

For an especially amazing display of flowers, arrange several varieties of bulbs together in the same container. Larger bulbs would be planted deeper, and small bulbs can be planted in a shallower layer above them.

Occasionally you may come across a bulb that has no discernible top or bottom. In cases like this, go ahead and plant the bulb on its side. Once it sprouts, the bulb will know which way to grow. The roots will always grow downward, while the leaves will naturally seek out light. 

The next step in forcing bulbs is very important. Spring bulbs need a chilling period before they will bloom, except for paperwhites which need no chilling period. Other bulbs must be given an artificial winter in order to be forced into blooming. This can be accomplished in a number of ways. The potted bulbs can be kept in the refrigerator, or in an unheated garage or cellar, or perhaps under a porch.

If you cannot sacrifice refrigerator space for several weeks and you have no unheated indoor area for the bulbs, they may also be kept outside in a protected area. Again, forethought is required for this, as you must dig a trench in the garden before the ground freezes. Place the potted bulbs in the trench and cover well with dry leaves or straw, then cover the whole thing with a sheet of plastic and anchor the plastic with stones or soil so the wind won’t catch it. Covering the bulb pit with plastic will make it so much easier to remove the pots at the end of the chilling period.

The length of time for the chilling period for forcing bulbs varies a bit, depending on the type of bulb. Daffodils and narcissus require a 15-week chilling period, along with crocus, tulips, grape hyacinths and irises. Hyacinths however, need only a 12-14 week chilling period. A longer chilling period will result in flowers that grow taller, while a chilling period that is not long enough may result in small plants that refuse to bloom.

Once the chilling period has ended, the potted bulbs can be brought indoors into warmer temperatures. Water the pot well and place it in a cool area indoors, such as a closed-off room or a cool basement. At this point it is not yet important for the bulbs to receive bright light. Leave the pot in this room for a week or two, until all of the bulbs begin to sprout. Once the bulbs have sprouted, the pot may be moved to a warmer, brighter area of the house, but not necessarily where they will receive full sunlight. Cooler temperatures, around 65-68 degrees Fahrenheit, will allow the bulbs to bloom for a longer period of time, but in general, forcing bulbs indoors does not allow them to bloom as long as they would outdoors in the ground.

Forcing bulbs to bloom indoors out of their natural schedule uses a great deal of the bulbs’ energy and is very hard on them. Do not attempt to force the same bulbs to bloom again for a second season. The bulbs will be too weak to bloom well, if at all. Bulbs that have been forced can either be discarded after the blooms fade, or they can be allowed to die back naturally and then stored in the pot until late summer or early fall when they can be planted outdoors. Even then it may take several years before the bulbs have enough energy to bloom again.

If you do wish to plant your forcing bulbs outdoors, the bulbs should be fertilized with a water soluble fertilizer while they are growing and blooming. If the bulbs are going to be discarded after they have been forced, no fertilizer will be necessary.

Forcing bulbs is a fun and inexpensive project that children will enjoy also. Imagine how much a child would enjoy presenting Mom with fresh flowers in late winter while the weather outdoors is still frigid. Try your own hand at forcing bulbs to brighten those late winter days when spring fever is at its height.