Bulb Forcing Chilling Time

Yes, it's early August and most of us aren't thinking about forcing flowers bulbs.  I know!  Here in north Idaho, the harvest season is just barely starting, my early started cherry tomatoes have produced 1 ripe one and the beans are still a week or so away.  Sadly, our raspberries are almost done and it was our best crop so far!  Of course when thinking about forcing flowers, you have to think months in advance, as they have a long chilling period.  Which leads to the topic today - chilling time.

Before I start, I probably should do the standard disclosures.  My wife, Cathy, runs Season Extenders, LLC. which sells the only product designed for forcing bulbs.  It also can germinate seeds.  These blogs will not be focused on selling The Bulb Box, but some of my experiments will likely involve it.

Now, on to the chilling experiment we ran.  So, what about the chilling requirements for tulips?  The Washington State University Extension Agency flyer on forcing bulbs states 15 weeks.  Online, I've seen other colleges state 15-23 weeks, and other postings online with as little as 10 weeks.  So, if I'm going to force tulips, do I have to let them chill for 15 weeks?

I decided to run an experiment where I didn't provide any chilling at all.  My expectations were that I'd get no flowers and perhaps no sprouting.  My results:

• Muscari - extemely delayed and strung out flower generation with normal flower height
• Tulips - extremely delayed flower generation.  Flower stalks were about 2 inches high, funny sort of burned look to them, odd and disfigured
• Daffodils - no flowering at all

The flowering was so delayed that those with normal chilling flowered before the no-chilled ones.


Another example is the picture of Muscari and Princess Irene tulips.  The Irene is listed as an early bloomer.  I suspect their chilling requirements are 15 weeks.  The ones in this picture have only 11 weeks:

All the tulips flowered, but note how tall (short) they are compared to the normal height Muscari.  They sure look pretty though and look even better when it's deep in the January winter!  Below is another picture with Princess Irene, Freeman, Tete a Tete, and again Muscari.  These have had 18 weeks chilling:

Comparing the Princess Irene against the Muscari in the two pictures really shows the shortening effect lack of proper chilling time creates. 

In closing the loop on this experiment, each bulb variety has it's special chilling requirements.  If you want pots with the tallest flower heights, you will need to chill them for the full period, which may vary if you have a mix.  However, after seeing my results, they still produce beautiful displays of color and allow me to display more pots during the winter season!

Till next time,
Darrell