Kelly: For you in zone 8, they can get pretty hot. I measured mine once with my compost thermometer. It was in spring, morning sun. I don't remember exactly, but the soil in the container was something like 10 degrees warmer than soil in garden beds while air temp inside the container was something like 20 degrees warmer then ambient air temp.

It will of course vary with your zone, season, daily weather, time of day, amount of sun...

Karen

I haven't done any measures on the SOIL temps, but after roasting some seedlings in the first year, I did check out the temperature of the air inside the containers vs the temperature outside the containers. The result on one particular day when the outside temps were 15C (60F) was that the temps inside the container ranged between 30C and 35C (upper 90s for you). These containers were in full sun.

Those in dappled shade were better off reaching about 20C (70F) which is ideal.

You also have to consider windy days. On those days the temps inside youe containers will be slightly lower because of the ventilation holes you will have in some containers.

In terms of all the things I can control, this is the only one I've lost seedlings to. Let me add that it only happened once. Lesson learned. :O)

Kelly, I really can't answer your question, I've never checked the temperature in my containers, other than to say it's warmer :) My ground is cold and wet right now (i.e. I couldn't do any major spading projects without destroying the soil structure - tried a couple of sample shovelsful yesterday)

Our PNW Z8 can confuse people not familiar with it because we are such a cool Z8 with much cloud cover and rain - other than in August and September. I can be gardening in a sweatshirt and boots in Spring, while my friend in Z7 North Carolina is back indoors with the air conditioning turned on by 11 AM.

Depends. (no help I know). I think mine are 10-15 degrees warmer. They are in morning sun until germination and then dappeled shade. I don't think there's a hard and fast rule. It just depends.