I was thinking about growing sugar beets on my London roof terrace, so I was wondering what temperature it needs. I also have access to a greenhouse should it be necessary.
In regard to the temperature requirements of sugar beets, they prefer an even 65°-80° Fahrenheit (warmer daytime temp) for the first 90 days of growth, at which point the roots begin to swell, and the plant will prefer to stay within 5° on either side of 75° Fahrenheit daytime temps, and the same for a 45° nighttime temp.
As for other optimal conditions:
Soil pH - Test your soil. The pH should read between 6.5 & 6.8. Sugar beets will produce poorly under that level, so if your soil reads lower than 6.5, apply lime.
Water - Sugar beets need at least 16" of rain to mature, but more is better. I have used about 35" over the entire season (counting rain) with success.
Fertilizer - These are heavy feeders. Give them plenty of nitrogen, in a balanced fertilizer, all season for the largest roots and highest sucrose levels.
Soil Type - They are adaptive, but do best in a sandy loam with a high organic matter content. It must be water retentive but free draining. I have grown them successfully in a range of soils, but still recommend sandy loam, even over bagged mix (no soil).
Other points of interest:
Sugar beets can take 100-180 days from seed to maturity, depending on conditions and variety. Some may take only 90.
In limited root space, go with a smaller beet. They take less space and mature faster, too!
Watch for weeds, which are the first reason for failure at first attempts on growing this plant.
I've noted that there is almost zero pest/disease problems when grown under close to ideal conditions, but watch for slugs, flea beetles, earwigs, and the like.