Everyday Science: Dormant Plants

We just moved to a new climate 2 years ago, and last year we planted our first plants in the garden.

There’s 5 of them.  I have a brown thumb.  I wanted to hedge my bets.

I spent the summer watching my new plants nervously.  Watching them, watering them, and waiting for them to die.

This might seem morbid, but you have to understand my history with gardens.  In the past homes we have lived in, and past climates, I successfully managed to find the plants that would grow best by reading gardening books, asking at Lowe’s, stalking my neighbors’ gardens, and trial and error.  I wound up with the most hardy native plants, ones that required little water above natural rainfall, and ones that would survive my gardening ineptness.

When we moved to Colorado, I got this book to prepare for another round of gardening failures, and found out…. I had been xeriscaping all my adult life!  Excellent.  I felt ready.

I planted my 5 Russian Sage plants and watched them flourish.  Feebly.  Then November came, and sure enough, they were dead.

Or were they?

I’m going to admit this because its in a blog, and you don’t know me or where I live.  Probably.  I actually snuck over to a neighboring subdivision and poked into their subdivision entrance display, which back in August I remembered had been chock full of healthy Russian Sage,….  and I broke a plant.  (Sorry, HOA people, but I’m sure your plant will be fine, just read this blog post!)   I snapped off a section to see if it snapped off just like mine did, and it did.  Excellent!  I think.

Again, you have to understand I have spent my adult life gardening in tropical climates.  We’re talking blue plumbago and hibiscus here, the ones that they grow in the greenhouse in Colorado, not outside…

I vaguely recalled something from biology class.  I’ll share.

Dormancy is a temporary state of slowed metabolism.  Plants go dormant in response to adverse growing conditions such as extreme heat or cold.  They go dormant in response to environmental conditions such as decreased amount of sunlight received in a day and colder temperatures.

What causes plants to react this way?

Plants have a hormone called abscisic acid (ABA) that contributes to the onset of dormancy.  When a plant is subjected to extreme conditions such as falling temperatures, ABA buildup allows the plant to deal with the stress by suspending growth of new foliage (in the vascular cambium, if you’re curious).

Abscisic acid levels in a plant are diminished by increased exposure to sunlight, warmer temperatures, and by heavy rains.  These conditions usually occur in the spring, of course.  Realize too that some winter-blooming plants are dormant in the summer months.  In their case, it would be cool fall rains that would trigger these plants to emerge from dormancy in the winter.

Plants have an internal clock that helps them remain in dormancy until it is time to grow again.  A certain number of cold days is required to break down the ABA within the plant and stimulate growth once more.  If there were an unseasonably warm day mid-winter, the plant would remain in dormancy, since its measure of cold days were not yet complete for the season.

When you force a bulb indoors, typically a late winter to early spring activity, you are actually triggering the plant to emerge from dormancy by introducing light and warmer temperatures.  (I have never actually attempted this myself.)

The levels of ABA differ from plant to plant, which is why some plants tolerate stressors such as cold winters more readily than others.  I’m guessing my Cape Blue Plumbago had much less ABA than does my Perovskia atriplicifolia.

For now, I think my Russian sage will successfully emerge from dormancy this spring ready for new growth.  But I’ll know for sure when it happens.

Helpful suggestions?  Comiseration?  Gardening pointers?  Leave a comment!

Resources:

Abscisic Acid.  Retrieved 10 Feb 11 from http://www.plant-hormones.info/abscisicacid.htm

What is Abscisic Acid?.  Retrieved 10 Feb 11 from http://www.essortment.com/abscisic-acid-61473.html

What Causes Plants to Become Dormant?.  Retrieved 10 Feb 11 from http://www.ehow.com/how-does_4914915_what-causes-plants-become-dormant.html

Nature’s Timekeeping.  Retrieved 10 Feb 11 from http://ceeldorado.ucdavis.edu/files/17562.htm