Hardiness zones

[b2smoov]

I'm hoping I can get some clarity on hardiness zones. I live in zone 10a. My understanding is that these zones are based on lowest expected temperatures. In 10a it does not get very cold. Obviously I will have better success with plants that like it warm. What about plants in colder zones? There is less chance of a bad frost but are those plants not able to tolerate the longer hotter summers and shorter colder winters?

Thanks for the help

Brian

 

[rockm]

It depends on the species. Some plants, especially temperate zone deciduous trees, are naturally "hard wired" to require given number of "chilling hours" below 40 degrees (or lower) to remain healthy. Crab apple, for instance, requires 400 hours (if I remember correctly) of temperatures at its root zone of below 40 degrees. The number of hours below a given temp depends on species, some can require less cold for shorter periods, others require colder for longer...

Colder climate trees, like crab apples and larches can limp along in warmer zones, but eventually decline and die over a period of years. Warmer weather trees in colder climates are easier because you can bring them inside a cold greenhouse or inside to avoid freezes...

THis is a complicated answer, but in short, bonsaists that I know of can grow plants that can be hardy to one zone above and one zone below their zone's location--IF they understand what precautions to take (cold greenhouse winter storage, etc.)