David, I think we have to look at climates of the Near East and Mediterranean regions, where astrology developed. The Mediterranean climate is similar to southern California, with cool rainy winters and long, hot dry summers. Winter wheat and barley, planted just prior to the onset of autumn rains, grew during the winter, and were ready for harvest in spring (barley) and early summer (wheat.) The important agricultural distinction is life-giving rain vs. summer drought, not heat vs. vs. winter cold. Virgo was probably an important month for the grape harvest; but otherwise was probably at the end of the long dry summer season. The autumn rainy season probably started in Libra or Scorpio. Anyway, check out a more modern book, Louise Riotte, Planetary Planting. The most fertile signs are the water signs. Venus-ruled Libra and Taurus are moderately fertile; with Capricorn having some fertility. Generally the air and fire signs (i. e., masculine signs) are not fertile.