Flower Bulbs: Use the Force!

It happens every year: my wonderful wife buys me a few bags of bulbs to plant in the garden (in case you didn’t know, tulips and many other bulbs are planted in autumn, to flower in spring). Plant as many as you can in autumn, and enjoy them in spring. There are also spring bulbs, such as begonias, dahlias and colocasias. They flower in summer in the garden or in containers.

I usually plant my bulbs using a bulb auger and a cordless drill (Note: if you hit a root with the drill, you risk twisting your wrist, so make sure you have a good grip). Sometimes I buy extra bulbs to “force” them in pots.

I have a good excuse this year for not getting my bulbs in the ground. I was in Hawaii when nearly a foot of snow fell in Anchorage, putting an end to our beautiful fall weather. With the ground frozen, the remaining bulbs were repotted and the pots stored in a crawl space or garage. I placed my forcing pots on the floor of my heated greenhouse, where it’s cooler than on the upper shelves. It’s possible to find unsold bulbs for sale at the end of the season in your area, but make sure they’re not dried out. They should sell for at least half price.

Vernalization

Tulips and other bulbs require “vernalization”, meaning they need chilling before growing them indoors. Outdoors, these bulbs are planted in the Fall (before freeze-up!) and will bloom in the Spring. But you can enjoy some early blooms by chilling and planting bulbs in pots indoors.

There is a lot of information online, which I like to review while I’m writing my post, but many sites fail to mention a critical step in prepping your bulbs. More on that later.

As always, buy the best bulbs you can afford. This goes for soil, bird seed and other items “yardeners” use. In the case of leftover bulbs, who can resist a half-off deal! You don’t have a lot to lose if something goes wrong.

Pre-chilling

Most bulbs need a cool period to start growing. I spoke to Brent Heath (of Brent and Becky’s Blubs), and he told me that your bulbs can be chilled in the “beer fridge” (i.e. an extra fridge WITHOUT fruit or vegetables) at 35°F (2°C) for several weeks (see list below for chilling time). Ethylene gas is released by ripening fruits and vegetables and aborts the flowering of your plants. I’ve noticed that many sites don’t mention this fact.

After pre-chilling, pot up the bulbs and grow at 50-60 F (10-15 C) degrees for 8-10 weeks. For tulips, place the flat side of the bulb toward the edge of the pot, pointy side up. Use a large enough pot to hold about 6 bulbs with enough depth for healthy root growth. Fill the pot to about ¾ of its depth  and place as many bulbs as will fit on top of the soil. Some may already be showing a small green shoot. Fill the rest of the pot to one-inch of the rim. Water weekly until more shoots appear. Keep in a cool place.

You can also avoid pre-chilling and pot your bulbs directly. Once the bulbs have been planted, place the container in a plastic bag (so that it doesn’t dry out too quickly) and put it in a refrigerator, a garage with little heat, a cold room or some other place where the temperature will remain above freezing, but below 10°C (50°F).

Since I don’t have a designated beer fridge, I’m just potting up the bulbs in my heated greenhouse and leaving the pots on the floor where it is cooler than the upper shelf space, giving them a bit of water once a week.

Professional Growers

Professional growers often force bulbs for display at flower shows, such as the Northwest Flower and Garden Festival (Seattle, Washington February 14-18, 2024. You should go!).  This requires a rather precise timeline to include the chilling, rooting and growth process at the desired bloom time. This may involve heat mats and lighting. Come to the show and you’ll see what I mean. ( Shameless self-promotion: I will be presenting a do-it-yourself workshop on making hypertufa troughs on Saturday February 17 at 3 PM. It’s called “Let it Rock!”)

Pre-chilled bulbs are also available for our friends in the south who don’t benefit from cool temperatures for forcing.

For the average human, just pot up the bulbs, keep them cool, water occasionally and then bring into the light and enjoy the blooms.

Forced bulbs generally don’t flower again, so don’t hesitate to compost them.

Cooling and Blooming Times

Amaryllis: no cooling required, 6-8 weeks to flower

Crocus: 8-15 weeks chilling, 2-3 weeks to flower

Iris: 13-15 weeks cold, 2-3 weeks to flower

Grape Hyacinth: 12-15 weeks cold, 2-3 weeks to flower

Hyacinth: 8-15 weeks chilling, 2-3 weeks to flower

Daffodil: 2-3 weeks chilling, 2-3 weeks to flower

Paperwhite: no chilling required, 3-5 weeks to flower

Snowdrop: 15 weeks chilling, 2 weeks to flower

Tulip: 10-16 weeks chilling, 2-3 weeks to flower