Zone Follies

What's your zone?  That might be a good conversation starter if you are trying to meet a gardener, but don't expect it to tell you much about what he is growing.  As any seasoned gardener will tell you, the U.S.D.A's zone hardiness map  is a nice starting point, but if that's all you consider, your garden will likely end up the Dead Zone.

My late, great Mexican bush sage. Hardy to zone 7b, but not in my garden.

I was reminded of the zone follies last weekend, when I journeyed 1,200 miles from Zone 7b to Zone 8a.   Now I am no stranger to 8a, since its boundaries are about 15 minutes from my 7b home.  Yet when I cross that magic line, I never feel as if I have entered another world. The flowers don't giggle and turn into Munchkins, the trees don't slap me if I pick an apple - all in all, things looks pretty much the same.  In fact, I have successfully grown several items that are technically Zone 8a plants - a variegated shell ginger, for example, and a nameless red sage I picked up somewhere that was not supposed to survive a 7b winter.

My 8a destination last weekend was Dallas, Texas - half a continent and an entire universe away, at least when it comes to plants.  There were no flying monkeys, but one quick look around told me I wasn't in Cary anymore.  Yes, there are some common denominator plants - crape myrtle, butterfly weed, switch grass, and the ubiquitous Knockout rose  - but the similarity ends there.  Its topography and its hot, dry climate are worlds away from the Southeast. So much for the zone hardiness map.

Back before I knew what I was doing, I did what every other novice gardener does: saw something pretty, checked out its cold hardiness, and stuck it in the ground.  Maybe it was my Northeastern, cold-centric mindset, but I  assumed that not freezing to death was the only thing a plant had to worry about.  Seven years and countless dead plants later (my kill rate is well over 30%), I have learned that winter temperatures are just the tip of the iceberg.  Heat, humidity, soil type, and annual rainfall matter just as much. 

Poppies, peonies, and tulips (hardy from zones 3-8) need a period of winter chill in order to flower.  Hostas  (also zones 3-8) always seem to look better in the north than the south.  They hate heat, as do fellow shade plants brunnera and pulmonaria, so don't be fooled by that zone 8 hardiness listing.  The agastaches I insist upon growing (zones 4 - 9) may do fine in Dallas, but they have trouble with clay and wet winters (hello, Cary).  For me, they will not survive more than a year or two, no matter how much Permatill and shredded pine bark I add to the soil.   Ditto those cold-hardy agaves and the biggest heartbreaker of them all, Mexican bush sage.

Thumbs down. Agastache hates heavy soil and humidity and never lasts in my garden.

Thumbs up. Alpinia comes back every year, despite its status as a zone 8a perennial.

Remember that Seinfeld episode in which George and Jerry ponder whether the opposite of tuna is chicken or salmon? Over the years, I have developed my own zone hardiness chart based on the Seinfeld-esque concept that every area has an opposite.  Cary, being special, has two opposites: the  Pacific northwest (cool and overcast is the opposite of hot and sunny) and the desert southwest (hot and dry is the opposite of hot and humid).  I have the highest failure rate with plants that are native to these regions.  You may think this says more about my gardening skills than it does about Cary's climate conditions,  but I think I'm on to something.  Can hundreds of dead plants be wrong?