Bulb forcing (the art of inducing plants to bloom out of season), brings a breath of spring cheer, color, fragrance and cheer to dark winter days. Pots of bulbs about to burst into bloom, also make wonderful holiday gifts. Miniature daffodils, tulips, hyacinths, crocuses, dwarf iris, scillas and others can be forced indoors from December through March. After potting up the bulbs are placed in the cold for about 9-13 weeks, then brought into the warmth of your greenhouse or home to bloom.

Choosing

If possible hand pick bulbs from a reliable supplier. Choose exhibition or premium, first-rate bulbs. They should be large, firm and unblemished. High quality bulbs are recommended as the bulbs contain the immature flowers and food required to produce flowering plants. Stay away from “Bargain”, damaged, soft and sprouting bulbs. You’ll save little and likely have disappointing results.

Containers

The type of container you choose is a personal preference. The only rules of thumb are that it has one or more drainage holes and is twice as deep as the bulbs you are planting. Bulbs will grow equally well in plastic or clay.

• Plastic pots do not dry out as rapidly as clay, are easier to clean, lighter in weight and generally cheaper. Bulb Pans and Azalea (3/4) pots are good choices.
• Clay pots are a traditional favorite for bulbs. The downside is that they do dry out faster and more care needs to be taken so they won’t chip and break.

If you are reusing pots make sure they have been scrubbed clean and that clay pots are soaked for several hours to saturate their pores before potting up.

Soil

The bulbs need moisture and good drainage. A good draining, commercial potting soil is most commonly used. You can prepare your own medium by mixing one part potting or garden soil, one part peat moss, one part perlite or vermiculite.

If you are going to plant the bulbs outside after forcing, add 1 tsp. of 5-10-5 dry fertilizer to every quart of soil mix to give bulbs an extra boost after flowering.

Mix well and moisten with enough water to obtain a damp consistency. Later while planting individual pots up you can add a pinch of bone meal per bulb.

Potting Up

1. Place a few pebbles, broken crockery or something similar over the drainage holes to prevent soil from running out the bottom.
2. Fill the pot about half full of soil.
3. For the best show, don’t intermix different kinds of bulbs in the same pot as they need different chilling times and have different bloom times.
4. Use a 4-6″ pot for smaller bulbs and a 6-10″ pot for larger bulbs.
5. Arrange bulbs on soil surface gently, with pointed end up, close but not touching, so they have room for root development.
6. Fill the container with more soil until bulb tips show just above the soil.
7. Water thoroughly from the top.
8. Label each pot. Include bulb name, planting date and date to bring inside for forcing. (See Bulb Forcing Schedule below.)
9. Mark your calendar to help you remember when to bring the first bulbs in to force.

Chilling

The bulbs now need cold (approx. 36-45° F.) and moisture to develop strong roots. Place them in a dark, cool spot. Possible suggestions are an insulated cold frame, under a porch, an unheated garage, cool cellar, old refrigerator or outdoor trench. You may need to set boxes, straw, or black garbage bags over your pots to keep them dark. Don’t let pots freeze.

Keep the bulbs moist, not letting the soil dry out totally – watering about once a month. To better hold in moisture you can cover pot surfaces with peat or sand.

Forcing

After 4-13 weeks of chilling,(depending on the kind of bulb) you will see roots emerging out of the drainage holes. Yellow shoots will also start to show from the top of the pots.
A basic rule of thumb is when you see the roots coming out of the bottom of the pot and 2-3 inch shoots coming above the soil it’s time to bring the pots into your home or greenhouse.

Now you are ready to mimick the arrival of spring with increased temperature and light!

For a succession of blooms during the winter bring in a few pots from outdoors every 2 weeks.

1. Transition the pots to a cool location where the temperature is in the 50’s. Light and temperature make all the difference between lanky, low flowering plants and robust plants with strong blooms. Caution: temperatures above 60° F will cause fast growth and few flowers.
2. Give them low to medium, indirect light.
3. Water them with houseplant liquid fertilizer at one half strength. . Keep them moist, but not soggy. Don’t let them dry out.
4. After buds appear mist with a sprayer, as a substitute for moist, springtime atmosphere.
5. When foliage and buds are well developed, approx. 1-2 weeks for most, pots are ready to move to a brightly lighted, 60-65° F. location.
6. After the flowers begin to open, to prolong their blooms, move them
   out of the direct sunlight and stake if needed.

After Care

Attempts at forcing the same bulbs a second time are usually unsuccessful. However, if you choose to, you can plant them outdoors in your landscape. Once they return to their natural bloom schedule, in several years, they will start blooming again.

After flowering cut the flower stems back and place in a sunny window. Water regularly until the foliage starts to yellow. A light feeding of fish or seaweed liquid fertilizer is helpful. As foliage withers, resist the temptation of pulling leaves off. Carefully remove the bulbs from the potting soil and let them dry for 2-3 weeks, then store in a cool, dry place until fall planting.

Bulb Forcing Schedule

Bulbs generally flower in 3-4 weeks after they have been moved to a warmer temperature. From time of planting to flowering you need to allow about 17-18 weeks. Remember it is easier to hold bulbs back than to speed them to bloom faster. Thus when you know the date you want them to be in bloom, calculate back to the best planting time.

Following are some examples. Times may vary dependent on the bulb type and if they are well rooted before being forced.

• To bloom in January-plant in September or early October
• To bloom in February for Valentine’s Day-plant early-mid October
• To bloom later-plant in late October or early November

Credit: wvgardengate.homestead.com

Looking for more info on bulb forcing? Download this useful PDF guide, “Forcing Flower Bulbs: How-To & What” by Richard Jauron of Iowa State University.