A microclimate is a local atmospheric zone where the climate differs from the surrounding area. Microclimates can have microclimates, which can have microclimates.
I live in the Beaches in Toronto, very close to Lake Ontario. This puts my yard in a microclimate caused by the lake – 6a surrounded by the 5b of the Greater Toronto Area. Being really, really close to the lake, and having a tiny yard sheltered by tall fences that gets quite a bit of western sun – my garden’s really more a 6b.
But even within the tiny confines of my yard, small micro-climates reveal themselves. The photo below is of three identical hostas. All Royal Standard, all planted at the exact same time, in the exact same manner, last summer. All within 12 inches of each other.
You guys don’t match at all.
Hosta Number One broke the soil over three weeks ago, and is full and lush and lovely. Hosta Number Two broke the soil about five days ago, and is about two inches tall. Hosta Number Three finally showed its head three days ago and is about one inch tall.
The image below shows what’s around them (the Astilbe and Blood Grass in the photo don’t count – they’ve only been there a week or two.
So – Hosta Number One sits out in front – unshaded by the apple tree, and getting a bit more of the hot afternoon sun before the shadow from the fence falls across it. It doesn’t seem like much of a difference – I’ve never measured the extra time that Hosta Number One spends in the sun, but I imagine it’s measured in minutes. Still – it made over three weeks’ difference to the hostas. That puts them in completely different growing zones, despite being about one foot apart.
So, when exploring your yard for microclimates, realise that it’s not just a matter of front yard vs. back yard – little things can make big differences.
This is a very simple example – microclimates can be caused by many factors, including soil and drainage. I’ve included some links below to more information from wiser people than me.