How To Force Bulbs Indoors

Last week we began to look at getting a jump on spring, indoors, in the middle of winter by forcing spring bulbs into bloom. But as I noted, the time to start this work is now, right now!

This week, the steps involved in the potting and chilling of the bulbs, how to do the forcing and some of my favorite varieties of tulips, hyacinths and daffodils that you can be successful with.

First, a little buying tip. Remember that the flower for the bulb that will emerge next spring has already been formed. There is little you can do now to make that flower bigger, but all these bulbs are graded by size and, for example, you may find one variety of tulip in three different size bulbs. The largest bulbs produce the largest flowers, and the largest bulbs are usually the ones sold singly and not prepackaged. In this case, bigger is indeed better.

Also consider that the different bulbs, and in some cases even different varieties of the same bulb, can require different cooling periods. Different bulbs also require different planting depths so make sure you know how deep they should be in the pot.

For these reasons this project becomes much more complicated if you try to mix and match tulips, hyacinths and daffodils in the same pot. It’s not impossible, but it does take some experience. For now, do different pots for different varieties. Still, if you have cooling space to experiment with then you can try mixing them up, but keep the smaller varieties, for example crocus, on the outside of the pot with taller varieties, like tulips, toward the inside. And keep notes so that in succeeding years you can learn from your mistakes and create some amazing forced pots.

Now comes the part that most people have trouble with, the cooling. Remember that what you’re trying to do is fool the bulbs into thinking that they have been planted outdoors in cool soil. As the soil temperature drops to the 50s and 40s, root development starts and continues until the soil cools to the 30s when the roots are finished growing. This means that the “forced” pots need to be either in a refrigerator, wine cellar, in an unheated garage or shed, in a cold frame or buried in the ground and covered with about two inches of soil. You can also put the pots on the ground and mound soil over them (use rodent repelling bulb dips or wire cages).

In the refrigerator, the potted bulbs should go into a vegetable crisper, where the humidity is higher, or inside a loosely sealed plastic container or plastic bags on a shelf. Remember that modern frost-free refrigerators suck the moisture out of the air — thus no frost. But the same refrigerator will suck the moisture out of your pots (and bulbs) and dry them out. The crisper or a plastic container or a plastic bag with a few “breathing” holes will keep the pots evenly moist though some water may need to be added in the first six to eight weeks of cooling.

If you have a spare refrigerator, you can even start your pots on the top shelf where it will be a bit warmer and then after a month or so move them down to the lower shelves where it will be several degrees cooler. You might even stuff the refrigerator and once or twice fiddle with the internal thermostat slightly to make it cooler; just don’t freeze the bulbs.

Burying the pots may present a bit of a problem. While the temperatures will be perfect, if the soil is frozen when you want to retrieve the pots, ya got a problem. The soil needs to be kept slightly moist, not wet, until they are frozen and may need watering if there is a thaw of a couple of days or more.

With some luck and cooperation from Ma Nature, by the first week of January you’ll have 12 weeks of cooling and your first pots can be brought into a warmer spot for a few days though the majority of your pots should have a couple of weeks or longer of cooling. Thaw the pots gradually and don’t rush them into a sunny bright room or they’ll force too quickly.

One year some of our tulips that were potted on October 29 were brought out of the cold frame on February 2 and flowered March 1, but this can vary from variety to variety because another tulip done at the same time bloomed a week earlier. As a rule of thumb, it should take three to four weeks to get blooms from the time cooling is stopped.

As the foliage begins to emerge you may want to insert two to three thin, foot-tall bamboo stakes around the perimeter of the pot to support the emerging leaves and stems that can get a bit floppy. The stakes can be cut to size as the flowers develop, and green garden twine can be used to create a cage around the stakes that will hold the plants upright and rigid. Once the plants fill in and bloom, the stakes and twine should be unnoticeable.

A good sign that a particular pot is ready to be forced or brought in is when you see roots coming out of the drainage hole in the bottom of the pot. While this works with tulips it may not work with all bulbs.

Unfortunately, once a bulb is forced it’s usually not planted in the garden. It’s kind of tough planting them in February or March, and their internal timing clocks are all screwed up, though some people tell me that they’ve had some success in getting forced daffodils to rebloom in the garden the following year. If you can keep the foliage growing until the ground is workable, tulips may be plantable. But it may be several years before they flower again so the cutting garden would be a great place for planting them.

Some quick tips: Bulbs should always go into the pots “nose,” or point, up. Tulip bulbs have a flat side that should face the pot rim. Double-nosed daffodil bulbs will ruin the blooming symmetry. A 6-inch pot will hold up to six tulips, three daffodils or more than 15 crocuses. Use a deeper pot and you can add layers of bulbs. Fill the pot — don’t leave spaces between the bulbs.

For those of you who want a shortcut, you can purchase precooled bulbs that are shipped in December and are ready for potting and forcing. I’ve never tried this route, but it may appeal to those who don’t have the space or ability to do the precooling at home. This link will take you to a supplier that offers a good selection of precooled bulbs: tinyurl.com/2p8e9vxz. Brent and Becky’s also offers a selection of precooled bulbs. Read the directions from the vendor before you make your purchase.

Here’s a short list of some bulbs that I’ve forced and been very satisfied with, and if you’ve got some favorites of your own please let me know.

Tulips (16 weeks): Cassinni, Merry Widow, Palestrina, White Hawk, Apricot Beauty (my favorite), Peerless Pink and Tambour Maitre. Try to avoid the tallest tulips as well as the very shortest varieties.

Hyacinths (12-16 weeks): Amethyst, Blue Jacket, Jan Bos, L’Innocence, Pink Pearl, Delft Blue and Carnegie.

Crocus (10 weeks): Pickwick, Remembrance, Peter Pan, Flower Record, Jean d’Arc, and Purpurea Gradiflora.

Daffodils (12-16 weeks): Barrett Browning, Brida Crown, Dutch Master, Ice Follies, Salome, Pink Charm, Tete-a-Tete, Jenny and Cheerfulness.

Keep growing.