Published Oct. 15, 2017, in the Wyoming Tribune Eagle, “An indoor spring…during the winter.”
By Barb Gorges
It’s the season for buying spring-blooming bulbs. But not all of them need to go in the garden—at least not right away. Some of them can be kept back for forcing.
Bulb forcing allows you to enjoy crocus, the small iris, hyacinth, daffodils and even tulips indoors earlier than they bloom outside. Think of them as a deep winter gift to yourself, or for someone else.
Cheyenne Botanic Gardens director Shane Smith recently gave me background on the practice and a few tips.
The science and history
Smith said the trick is to use bulbs from temperate climates that need winter—such as the bulbs we plant in our gardens for spring bloom. They can get by with a shorter winter, or artificial cooling period, to bloom. Bulb growers in Europe started taking advantage of this about 300 years ago, as relayed by Patricia Coccoris of Holland in her book, “The Curious History of the Bulb Vase.”
Buy spring-blooming bulbs now. Bulbs ordered from catalogs begin shipping here around the beginning of October because bulbs normally need to be planted outdoors when the soil cools, but before it freezes in December.
For bulb forcing, figure 12 weeks minimum of “cool treatment,” however tulips need 13 weeks or more. Once the minimum is met, you can stagger when you start warming up the bulbs. You can aim for specific bloom times during our cabin fever months, January through March, or maybe even later into spring when we get those depressingly late, tulip-breaking snow storms.
The best bulbs
Smith said he used to tell people to buy the premium-sized bulbs for forcing, but now he thinks he gets more bloom for his buck with the smaller grades of bulbs. Premium hyacinth bulbs go for more than a dollar apiece in the John Scheepers catalog, but you might find smaller bargain bulbs and have more, if only medium-sized blooms, for the same amount.
Smith said some varieties of bulbs are easier to force and bulb catalogs often will mention which ones. Varieties seem to go in and out of vogue so don’t be surprised if Smith’s are hard to find.
Hyacinth is the classic forcing bulb, growing 10-12 inches tall. Each stalk is covered in tiny florets. Smith looks for Pink Pearl, Queen of the Pinks, White Pearl, L’Innocence (white), Blue Jacket, Delft Blue and Blue Giant.
All varieties of crocus force well. Smith’s favorite varieties are Remembrance (purple), Blue Ribbon, Giant Yellow and Jeanne d’Arc (white). Only 4-5 inches tall, they are usually planted as a mass.
Iris reticulata, though related to the summer-blooming bearded iris, grows only 4-6 inches high. Recommended for rock gardens, mine bloomed outside at the end of last February, but it would be nice not to have to brave winter winds to enjoy it. Smith said all the varieties force well. Scheepers lists eight ranging in color from white to blue to deep purple, all marked with a bit of yellow.
Almost any daffodil (narcissus) will work well for forcing, said Smith. The popular Paperwhite narcissus, however, is a tropical bulb, so it doesn’t need cooling.
Tulips, said Smith, are the hardest to force. They need the longest cooling time, minimum 13 weeks. They also may get floppy and need staking. Look for the earliest varieties, those that would otherwise bloom outdoors here (winter-hardiness zone 5) in April.
There are a variety of other, more difficult spring-blooming bulbs to experiment with: snowdrops, grape hyacinth (muscari) and squill (scilla).
Bulb-forcing vases are not easy to find this fall. Your best bet is Amazon or eBay. These vases, usually glass, are pinched near the top, providing a cup for the bulb to sit suspended so that only its base touches the water. You watch as the roots grow to fill the rest of the vase and the flower stem sprouts. For this forcing method, you can cool just the bulbs in your refrigerator for the recommended time. Be sure hyacinth bulbs don’t touch produce.
If you are lucky enough to find a bulb forcing vase, remember to change the water regularly.
These hyacinth bulbs have been potted up and will be set in a 2-foot deep trench in the vegetable garden and mulched with straw or pine needles for their 12-week “cool treatment.” Small bulbs, like crocus, need a half inch of soil covering them. Photo by Barb Gorges.
Smith pots his bulbs. Without a cellar between 35 and 45 degrees, he instead buries the pots in a 2-foot-deep trench in his vegetable garden. He then backfills the trench with straw or pine needles. The mulch allows moisture to percolate down, whether the bulbs are watered by hand or by snow, and allows in air.
Pots can be plastic or clay. However, if you have a fancy one, you may want to use it as a cache pot in which you insert the utilitarian pot that was buried.
Put only one type of bulb in a pot because different types sprout at different rates.
The depth of the pot should allow 2 inches or more of potting soil under the bulb with the bulb tip just a little below the rim of the pot.
Smith said regular packaged potting soil will do. Potting soil can be very dry, so mix it with water in an old dishpan or bucket before spooning it into the pot as the layer that will be under the bulbs. Then set the bulbs on top, right side up. The root end can have bits of root left and the shoot end is usually pointier.
You can pack the bulbs in, nearly shoulder to shoulder, leaving just a little space between them. Then fill in with more potting soil. Smith said the top third of the bulb can be left exposed, but crocus and iris bulbs need to be covered a half inch deep.
Label the pot so you remember what’s in it—especially if you do more than one kind. Mark where you bury the pot. And mark your calendar for when to bring the pot in.
While the potted bulbs are chilling in the dark, make sure the soil doesn’t dry out. You may need to lift the mulch and water once a month if it’s a dry winter.
Coming in from the cold
When you bring a pot in, Smith recommends putting it in a dim room at 60 degrees or cooler until the shoots are a few inches tall. Then move it to a bright window and 65 degrees. “Buried to blooming” may take two weeks. Turn pots every day to keep plants growing straight.
Flowers can last a week or two. Once in bloom, you can prolong it by setting the pot farther from the window and keeping the room’s temperature at 65 degrees.
The advantage to planting forced bulbs in potting soil is that you can give them a second life. Cut back the spent flowers and keep watering until the leaves turn yellow. Plant the bulbs out in the garden when the soil thaws, where they might bloom again in two years.
Update March 1, 2018:
The bulbs for the vases were left in the refrigerator for a couple of months to cool and taken out in early January.
Also in early January I brought in the pot of hyacinth and the pot of crocus that were buried in the vegetable garden and covered with a foot of leaf mulch.
The bulbs in vases didn’t do well. They couldn’t seem to grow enough roots. That hyacinth stalk of flowers was about 15 percent the size of the ones in the pot.
I felt sorry for the crocus bulbs in the tiny vases and soon planted them in dirt where they were much happier. That proves you could cool your bulbs in the fridge and then plant them in soil, without wintering them in the garden. But the pot of crocus that did spend two months buried did very well. Interestingly, the yellow crocus bloomed before any of the shades of purple.
I would force bulbs again. If I plant the hyacinth bulbs individually, they would be easier to share with friends, or I could stagger the dates I bring them indoors, prolonging the season of sweet-smelling flowers.