Expert: Long Island Gardener - 3/13/2007

Question
I hope you can help me.  A friend of mine gave me a Geranium Tree (that is what she called it) a few years ago.  It looked exactly like a geranium plant when it was little, but grew outside to about 7 or 8 feet tall.  It had light pink flowers on it, and came back every year, despite the fact that we sometimes get frost or below freezing temperatures here in Southern Oregon.  The next year, I found baby geranium trees growing in the same area, even in gravel.  Do you know if this is the proper name for this tree/annual/perennial, and do you have any information on it?

Answer
It is my understanding that the ubiquitous Pelargonium, the "Zonal Geranium", is in fact hardy to 28 degrees.  It can that kind of cold if you harden it off carefully -- if it "gets used" to cooling weather.

That's what happens as a plant produces "anti-freeze" to protect delicate tissues.  Specialized cells speed up production of soluble solutes (sugars, salts and other chemicals) that lower the freezing point of water inside the plant.  These solutes stop ice from forming and rupturing cell membrances.

Not all plants of course can do this; most truly tropical plants will fizzle instantly at the first breath of frozen air.

But many are borderline-hardy and can take a little cold weather, given the time to build up the necessary levels of "anti-freeze".

Although Geraniums, cannot, hardier plants will survive formation of ice crystals in tissues because the water does not freeze inside the cells -- just outside and between them.  Trees growing in Northern latitudes of the U.S. to can do this.  Water freezing in these special tissues forms ice crystals outside and between cells.  As temps steadily plunge, more water moves out of the cells and into the spaces; more sap is produced to keep tissues from freezing.  Any plant that endures frigid, bitter cold winters must be able to tolerate lots of ice between its cells and survive a certain level of dehydration with minimal injury.  Geraniums cannot of course take this kind of cold.

But your mild South Oregon winters are evidently not so extreme.  And your Geranium is surviving.

Assuming this is in fact a Geranium that has gotten large enough to be called a Tree -- many "trees" are shorter.  Check the online catalog for Geranium-specialist Logee's (http://www.logees.com/default.asp) -- type "Pelargonium" in the "search" box to get their Zonals list -- to confirm for me that these are smaller versions of Pelargonium.  And let me know.