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Spring Bulbs; The Rules for Rebloom are the Same around the World


You Bet Your Garden
Question of the Week © 2018 Mike McGrath

Note: Hundreds of Mike's informative articles are available (in alphabetical order!) right here at the Gardens Alive website. To find Mike's answers to your specific garden problem, Click here and find your topic (like Weeds, Worms, Rhododendrons...) in our complete alphabetical archive of Questions of the Week.

Spring Bulbs; The Rules for Rebloom are the Same around the World

Q. I bought tulip bulbs, refrigerated them for a few months, planted them last fall, and now they are blooming. I read your wonderful explanation of how you have tulips that are now teenagers. I will follow those instructions. But I have a question: If I put the tulip bulbs in paper bags and put the bags in the refrigerator, will they propagate? Or do they propagate during the time when their leaves are still green to produce the next year's flowers?

---Arabella "in the Kyushu {"Q-Shoe"} Prefecture of Japan"

A. My research tells me that 'Kyushu' is a volcanic island located off the Southwest tip of Japan. It's the third largest of Japan's four islands and is home to an astounding 13 million people.

Yes, the volcano is active. And other parts of the island are like Yellowstone, with hot springs, boiling geysers and mud flats. The volcano—which last blew in the 1990s—is near Nagasaki, the port city where the second atomic bomb was dropped to end World War II. Now—we don't know exactly where Arabella lives on this remarkable piece of land, because "Kyushu" is the name of the entire island, which contains seven different prefectures, including Nagasaki.

I suspect that Arabella refrigerated her bulbs because the entire island is semi-tropical and doesn't appear to ever drop below freezing; and all Spring bulbs require a chilling period before they will bloom again.

Now, 'chilling' doesn't require actual freezing temperatures, but it sounds like she could be in an area where it still doesn't get reliably cool enough in winter to insure Spring bulb rebloom. But before we get to that, let's repeat the basic rules of Spring bulbs.

You plant the bulbs in the Fall; after Halloween and before Thanksgiving in our mid-Atlantic region. (Earlier in really cold climes; even later in warm ones that provide enough of a natural winter chill.) The shoots emerge and the flowers bloom in the Spring; first up are crocus and other small-flowered bulbs, then daffodils and then tulips. As soon as the flowers fade, you clip off the seedhead that forms at the top of the central stalk and give the plant a gentle feeding, because this is the time it needs the most energy.

That's also why you MUST leave the green leaves alone.

This is essential. The plant needs those leaves to absorb the solar energy that will fuel the growth of the following year's flower. By the time those leaves lose their green, that flower will already be fully formed inside the bulb (which is really cool).

After the greens have turned brown, you can clip them off. If you want to plant something else in the same spot, it is wise to dig up the now-dormant bulbs and store them indoors. This is the phase where they want to be dry and undisturbed.

Then you'd replant the bulbs in the Fall. Or, if you're in a climate too warm for good chilling, refrigerate the bulbs for at least 12 weeks; 16 weeks for tulips, as they need the longest chill time of any Spring bulb—ideally at 40 to 45 degrees Fahrenheit (which is five to seven degrees Celsius; the method used in Japan).

When I 'force' bulbs by chilling them indoors, I pot them up in loose soil, water them once and put them in an old beer fridge in my basement. If Arabella is short on fridge space, she can chill them unplanted. Just make sure no fruit of any kind is in the fridge, or the bulbs could sprout prematurely.

Now, what about the 'propagation' she mentions?

Tulips don't spread wildly, as grape hyacinth does naturally, but there are propagation tactics to try. The first would be to save those clipped-off seed heads and put them through the same regimen as full-grown bulbs; you'll only get leaves for the first several years, but eventually they should flower.

The second is to carefully harvest any 'offsets' you find. These are structures that look like smallish bulbs or flattened cloves that form next to the mother bulb. Put them through the same regimen of planting and chilling and they will eventually produce flowers. The key with both tactics is to be patient; this kind of propagation takes a long time.

And what if she simply meant insuring their return year after year, like what she calls my "teenage tulips"?

Those simple red tulips—the most reliable type of tulip to return—are now over 35 years old. (Their exact age is unknown, as they came with the house and appeared to be very well established when we moved in in 1985.)

Why do they return so reliably"? They get good sun; I always clip off the seedheads to direct all the energy of the plant down to the underground bulb; I always leave the green leaves alone until they're good and brown; and I don't grow anything else overtop of them.

P. S. Here's a great map of Arabella's island with lots of info on the different prefectures.

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