According to my grower's reference guide, the minimum temperature for these should be: Ficus: 65F (18C) but can tolerate "brief spells of cool[er] weather." Schefflera: to 35F (2C), but best above 60F (16C). Epipremnum (pothos): damage begins at 55F (13C), best at or above 60F (16C). Chlorophytum (spider): to 35F without damage, but growth will slow severely starting at about 65F (18C). So, to keep them all happy, probably no lower than 65F, though you might be able to get away with something in the 55-60F range.

I have been having the same problems here in Kansas. I have 102 plants in one hoop building. They have been there since March 28th. They are growing great, minus the ones that died when it was 18 degrees. It is 50-80's in the day and 32-50 at night. I have been covering them up with row cover every night it is suppose to be below 45. Then take it off each morning. It is alot of work, but I can tell you that I am seeing more growth this year than last because of it. I also have 400 seedlings in another hoop house. They are under one layer of row cover also. They have been out there for a week. They went straight from the basement lights to the hoop house during a cloudy 3 day warm spell. They were not stressed. I don't get too worried about 40's, with the hoops. I do start to worry when they say 38 or below. I just double up the row cover. After the 18 degrees and had a majority of everything come through ok, 32 doesn't scare me like last year. Do I worry, a little, but I still sleep good. Jay

"zone numbers don't mean much in terms of temperatures. " Actually, that's exactly what zone numbers mean. :) Hardiness Zones don't tell you the length of the growing season; they tell you the average minimum temperature for a given location. Your Zone 8 means it gets down to an average of 10-20 degrees in the winter. Austin, TX gets down the same average lows, so your areas are both listed as Zone 8. But that doesn't mean your last average frost dates are the same, or that your average temperatures through the summer are the same, or that your growing season is the same length. All Zone 8's (or Zone 5's in my case) are not the same, so just because someone in TX has planted their tomatoes outside doesn't mean you're behind if you haven't. In general, Zones are more useful information for perennials -- will they survive the winter low temperatures -- than for annuals. That's why you see perennials marked with "Z5-8" or whatever, but you don't see vegetables identified that way. An area's average last & first frost days are more useful information for vegetable growing. The attached link explains it well, bringing in Heat Zones and how Washington significantly differs from Texas, even though they both are in Hardiness Zone 8. Kathy Here is a link that might be useful: Washington State Extension - Hardiness Zones

I asked because I know that when air temperature reaches 85 degrees the stoma under the leaves begin to close. By 90 degrees they are closed and photosynthesis essentially shuts down as no CO2 can enter the plant as stoma are closed. Southern growers us shade cloth to lower the air temperature around their plants. A 40% shade cloth can lower the temperature by 10 degrees. Misting can add to that. This allows photosynthesis and thereby tomato growth to continue. With direct sunlight in summer a tomato plant only uses 50% of the light energy available. So with a 40% shade they still get enough light for growth and are yet have a better chance to be cool enough to have their stoma open. The reason I asked about leaf temperature is that I wondered if someone here had an interest in it and knew anything about it and its effect on tomato growth. Think about it Carolyn. It is just another piece to the puzzle of knowing all you can. My puzzle has a lot of pieces missing.