Differences between zone 9 & zone 10 (besides avg lo temp) ?
It's been awhile since I asked a dumb question, so here I go to stay in practice...
When I look in garden catalogs and plant databases, I notice a lot of plants listed as zone x - 9. Some of them are ones that do fine for me in my coastal So. Cal Zone 10 (e.g. daylilies and species tulips). Others will simply not work (e.g. bignonia/crossvine). I understand the difference between the two zones where there are chilling requirements and low temps make a difference. But what about a plant, zone x-9, that does not require a chilling period? Why will that plant survive in a zone 9 but not just one zone higher? Living by the sea, I don't often get extreme hot/dry days like in the desert, so I feel there's very little difference between my zone and zone 9 during the hot months. What are the considerations 'they' factor in when identifying a plant's zone with regards to the high end of the temperature range?