What is the ideal temperature for growth for an Aeroponic Garden?
A terrestrial plant maintains a greater range of temperatures in the parts above ground (canopy), and usually lower and more stable temperatures below ground. The same applies for aeroponics. The root zone should be kept between 62°F - 71°F. This is because the highest dissolved oxygen occurs at 68F (9ppm DO), and oxygen is transported inside the plant as dissolved oxygen even though the air roots might be exposed to higher oxygen levels. However, it should be noted that some plants, such as lettuce, are less sensitive to levels of DO then other plants.
The canopy can be kept at higher temperatures. The leaf temperature range for fast growth is 72° (minimum) to 86°F. As a rule of thumb plant growth approximately doubles for every 10°F rise.
Within limits, rates of photosynthesis and respiration both rise with increasing temperatures. As temperatures reach the upper growing limits for the crop, the rate of food used by respiration may exceed the rate at which food is manufactured by photosynthesis. For tomatoes, growth peaks at 96°F.
The temperature may also need to be lowered when plants flower and fruit. Chilling the nutrient solution also helps protect the plant against heat stress, and lower temperatures are used for cool climate plants.
Note also that lighting has an effect on the plant. LED lighting does not generates infra-red and so has no major effect on plant tissue temperatures, but HID lighting can raise tissue temperature by 5-7°F which is why it only appears that LED lighting is not as effective as high intensity discharge lighting. The effect of IR heating forms a gradient on the plant as distance increases from the light source.
CO2 requirements rise with temperature, and enriching the grow room with CO2 does allow also for higher temperatures.
At night you can drop the temperature by 10°F from the day period.
The optimum temperature is somewhere in the range between 70F and 95F - the specific optimum(s) certainly vary by species and even cultivar.
Simple chemical reaction rates increase rapidly with temperature. This means that metabolic activity and growth tends to increase rapidly with temperature. The same is true for photosynthesis except that the activity of the key enzyme RUBISCO saturates (stops increasing) at a temperature in the neighborhood of 90F. So, above 95F (or thereabouts) metabolic activity outpaces the rate of photosynthesis and growth ceases.
Rooting of cuttings is often done with bottom heat. Temperatures around 70F are most frequently used in large scale production. It seems reasonable to presume that this might be the optimal temperature for root growth and hence a lower limit to the 'ideal temperature'. Nevertheless, roots may indeed grow faster at temperatures above 70F (i.e., this 'optimum' maybe occurs because of factors unique to rooting cuttings, such as the need for minimal transpiration).