On Oct 28, 2005, at 12:14 PM, Susan Hayek wrote: >> Even >> tomatoes stop producing new fruits during the peak hottest summer >> months in Austin--because the nights never cool down enough to let >> them >> form. (They've bred a few special heat tolerant varieties that can do >> it, and cherry tomatoes seem to already have that ability.) In >> California, even in areas where the days are hotter in summer than in >> Austin, the nights are still cooler and tomatoes fruit all summer >> long. > > **I'm confused on the tomato thing. My parents lived in the > California Central Valley for years (from 1952 on), Bakersfied, Taft, > Fresno and Kerman (south portions of the Central Valley). Days can > be well over 100F and nights may cool to 95-97F at 2 am. When I went > over to help them I did the gardening after midnight. > > They always had the best tomatoes, the huge ones (and the best roses). > So when we talk of nights 'cooling' how do we define 'cool'? Do we > mean certain amount of degrees less than afternoon temps? Or do we > mean a set temperature? > First off, I believe the night time low temperature point above which tomato fruits start having difficulty forming is around 70 or 71°F. If it doesn't regularly drop below that temperature for long periods of time, then no fruit form and 30 days later or however long it takes to ripen, there won't be any fruit to ripen. Here is a PDF file from Alabama that describes this facet of tomato growing and the new 'heat set' tomato varieties that have been developed. <http://aces.edu/department/com_veg/…> Here are the monthly average maximum and minimum temperatures for the warmest months of the year for Bakersfield and Fresno, and for the triangle of Dallas, San Antonio, and Houston (as well as Austin) in Texas, which covers a much larger area than the south Central Valley of California. Remember than each number is the average of approx. 30 low or high temperatures (for each day in a given month) times 30 years worth of data. I.e., each value is the average of about 900 individual high or low temperatures measured during that month of the year. So of course sometimes the low will be higher than this and sometimes the low will be lower than this value. So it gives you an idea of about what you can expect the low temperature will be on any given day of a given month in that locality. Looking at the California lows (especially in July and August) and comparing them with the Texas lows (for June, July, and August), even though I'm sure there are days in the summer in Bakersfield or Fresno where the low temperature didn't drop as low as the average, enough did that the average, even in Bakersfield, even in July, is still below the 70-71°F critical point. Another thing to keep in mind is that the summertime temperatures in Texas are remarkably consistent day after day year after year. They virtually never get any kind of cool front all summer long. Morning after morning for weeks on end, the temperature always drops to 72, 73, 74 or 75°F and no lower--not from some time in June until sometime in September does it get any lower. May Jun Jul Aug Sep Oct Bakersfield, California 84.6 92.3 98.4 96.4 90.0 80.6 57.2 63.9 69.4 68.4 63.5 54.7 Fresno, California 84.2 92.7 98.6 96.6 90.0 79.7 53.6 60.3 64.9 63.7 58.6 50.5 =============================================== May Jun Jul Aug Sep Oct Austin, Texas 84.6 91.0 95.0 95.4 90.5 82.0 66.4 71.4 73.8 73.8 69.8 59.9 Dallas, Texas 82.8 91.8 96.4 96.1 87.8 78.4 62.6 70.0 73.9 73.6 66.7 55.8 Houston, Texas 84.7 89.8 92.3 92.3 88.0 81.3 66.9 72.5 74.5 74.5 71.1 61.2 San Antonio, Texas 85.3 91.8 95.0 95.2 89.2 81.7 65.7 72.5 74.8 74.5 69.1 58.6 --Lee Poulsen Pasadena area, California, USDA Zone 10a