A Gardening Journal

Today in the Garden of a Lifetime: Jacaranda in Bloom

In San Diego, the meanest Winter temperatures feel like Spring in New England: mid to low forties. Even so, Spring-blooming jacaranda goes by the calendar, not the weather, and waits until late May to flower. My pair of jacarandas overwinter in a greenhouse that, in the short gray days from December through February, can be barely warmer than fifty degrees Fahrenheit. That seems a lot like Winter in San Diego, so why haven't they waited until late May to flower?  

 

Jacaranda mimosifolia other 041515 640

 

There are also broader questions: What controls any plant's dormancy? How much flexibility does any given plant have in tolerating a dormant period that is shorter or longer than what it would experience in its native climate? With hundreds of thousands of plant species native, in the aggregate, to every climate on the globe, there are many different strategies to achieve dormancy and survive the rigors of the off-season. Here are only a few: dropping leaves, dying to the ground, reducing the need for (and tolerance of) water or bright sun, tolerating (or even requiring) a certain intensity and even duration of heat or cold. 

 

Jacaranda requires a frost-free environment during the Winter if it is to flower in Spring, so prolonging its dormancy isn't a matter of, say, providing an even more severe freeze. Jacarandas aren't lilacs or peonies! But even a decrease of just a few degrees of temperature might be a help. Plus a much less free hand in resuming generous watering the moment the buds at the tips of the tree's stems seem to be swelling. And why keep a dormant plant that's leafless in a spot in the greenhouse that receives the maximum amount of direct sun?

 

I have a pair of jacarandas, and I've always stored them side by side in the greehouse. No surprise, then, that they've behaved the same—this Spring by coming into bloom many weeks before I'd prefer. In just six months, they'll return to the greenhouse for the coming Winter. I'll handle each tree a bit differently—keeping one at the shady (and therefore a bit cooler) corner of the greenhouse, say, while showing the other more tough love when it comes to reducing and or witholding watering. Perhaps one or both strategies will help these jacarandas remain dormant long enough to begin flowering only after they've returned to the garden.

 

Here's how to grow jacaranda; see the second "How to handle it" box for tactics for helping a containered jacaranda delay flowering until the weather is warm enough to bring the tree back out into the garden.

 
 
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