Bulb forcing

Got a pot, some tulip bulbs, and some dirt? You’re set! That sounds too simple, I admit. I know online courses exist that charge a lot of money to teach bulb forcing in more detail, but it is very basic. I’m sharing the process we’ve followed for 5 years, adapting as we made mistakes and learned what works for our small-scale business. If you want to try this on a micro-scale and have a few flowers just for yourself or a special occasion, these steps can be adapted to your needs.

Right now it’s bulb ordering time for flower farmers, even though my crop for 2025 is still buried under snow. If you aren’t particular about what bulbs you want to try forcing, a good selection is available through retail outlets in the fall. I order wholesale quantities with specific colour schemes for weddings and events in mind, so I try to get my lists in early to my bulb suppliers. When my order is confirmed, I select a shipping date at the end of October. Whatever I’m forcing gets set aside while we plant the rest of the bulbs in the ground. Once all the outdoor work is done for the year, we plant the bulbs for forcing.

Narcissus ready to be covered with Promix potting soil

We plant our bulbs in plastic crates saved from our tulip shipments. We line them with newspaper to hold the soil, place about 2” of wet Promix potting soil in an even layer, and then space the bulbs close but not touching. The bulbs are covered with more Promix, ensuring the tops are below the soil by at least an inch. The plastic crates stack neatly in my cooler, saving space. Smaller bulbs like muscari are planted in plug trays for forcing. To have a beautiful bulb garden that can bloom in your house, plant your bulbs using the same method but in a terracotta pot. Any plant pot will work as long as it has a hole for drainage.

While the equipment required for bulb forcing is minimal, the variables of light, temperature, and time determine your results.

Before planting any forced bulbs, I consider bloom time. When do I want these? Do I have a late April wedding that requires fresh flowers? Are these an addition to my spring bouquets for markets and subscriptions? Or am I trying for Valentine’s Day sales? All bulbs require a chilling period of 10-13 weeks for the roots to grow and to break what is called “stem dormancy”. If they don’t get enough cold during dormancy, they will bloom on short stems, often with the flowers barely about the soil level. For bulbs in the ground in my garden, this isn’t a problem. We get months of cold weather. For bulb forcing, we have to recreate a long, cold period. I do this with my cooler and a small heater attached to an Inkbird thermostat. This keeps my cooler at roughly 3C. Crated bulbs don’t have the insulation of a deep layer of soil to withstand freezing temperatures. They can’t be left outside with no protection. If you don’t have a cooler like me, you can put potted bulbs in a garage that stays above freezing all winter. Other creative solutions like cold frames insulated with leaves and straw can be used in places without bitterly cold winters like Alberta.

Once our bulbs are chilling in the cooler, we monitor the temps inside with a weather station. I want it to stay a consistent 3C as much as possible during the winter. If we get a warm spell of more than a day or two, I will get Fiona to pile snow on the crates to keep them cold. This winter the door to the cooler was left open a crack by accident during a cold snap of -35C. I thought the bulbs might have frozen and I would be out a lot of flowers and money. Luckily, they didn’t freeze and rot. We water minimally during the chilling period, only topping them with snow if the soil surface feels dry. It’s important to note that some bulbs are sensitive to fluoride, so we don’t use our tap water on them. Keeping the bulbs very cold, but above freezing temps is essential in timing them to bloom when you want them. In years when I am forcing bulbs to go with tulips that bloom in May, we must switch from heating my cooler to running my CoolBot to keep the temperatures at 3C as the outside temps can swing quickly from below freezing to 15C or higher in spring.

After 12 weeks of chilling in the cooler, we check the crates for signs of leaves poking out of the soil. Now they can be “forced” into bloom and have nice long stems. They can also be held at 3C until needed. When I want blooms, I plan to pull crates from the cooler about 3 weeks before I need the flowers. Some flowers may bloom a little sooner, but I’ve found it takes 3 weeks in my heated garage to get a good flush of flowers. The temperature in my garage runs between 6-10C in the winter. It’s not much warmer than the cooler, but they sit on the heated cement floor, warming the soil more than the air temperature. If I hold the crates in the cooler long enough that we no longer have freezing temperatures at night, they are moved into a shady spot in my yard. It’s important not to put forced bulbs into direct sunlight when they’ve been in the dark for months.

I don’t use supplemental light when forcing bulbs in late winter or early spring. The natural light from the windows in my garage is enough to produce flowers. If I’m putting bulbs outside, I make sure they sit in the shade for most of the day. Just as I use shade cloth on my outdoor tulip crop, I ensure that all bulbs I’m forcing do not receive full sun. This helps to produce long stems.

Once my crates of bulbs have finished blooming, we continue to water them and add a layer of compost and some organic fertilizer to nourish the bulbs. When the foliage dies back, we clean up the crates and stack them out of the way until the killing frost. They go back in the cooler and we force them a second time. After the second cycle, I empty the crates and check which bulbs are still viable. After two years, most large bulbs like narcissus start to naturalize and become too crowded to continue being crate-grown. If the bulbs still look good, I will plant some in my yard. Otherwise, I toss and start the cycle over. Second-year crated bulbs will start to produce earlier than the previous year because they don’t have to go through the rooting process. We learned this the hard way when some of our crates started blooming in the dark of the cooler, producing pale, ghost-like flowers. We check earlier now so we don’t waste blooms. Another way to manipulate the bloom time is to hold the bulbs in the cooler, not planted, until January. In a year when Easter falls late in April, this gives us a nice flush of crated blooms for our customers that we wouldn’t have otherwise because our field flowers never bloom that early.

So, what bulbs can you force this way? So many different flowers are good for forcing.

A short list of what I’ve tried:

1) Tulips- I did this one year and decided it was not worth it when I couldld grow better ones in the field

2) Narcissus- my favourite bulbs to force. Field grown narcissus are very short and many are not hardy to our Zone 3 winter

3) Hyacinths- another favourite that doesn’t tolerate our harsh winter, so forcing them is my only option

4) Leucojum- similar to narcissus, this bulb does not grow well in the field for me but is beautiful when forced

5) Muscari- this grows well in the field but is super short. Forcing them gives me a long usable stem

6) Camassia- last year was my first year trying this beautiful flower. It’s another one that can’t tolerate our winter.

7) Eremurus- we trialed this in crates and found it is too big and needs to the space of the field.

I’ve narrowed down my list of bulbs for forcing to those that I can’t grow well, or at all, in the field. I’m still experimenting with different crops that could be successfully forced in my minimalist setup to add more variety to my spring bouquets.

If you’ve got some space that stays cold but not freezing, give bulb forcing a try this winter. You’ll be treated to some early spring blooms while everything else is still just waking up!