The following two books would be most useful in helping you to choose the best varieties for your area. Your local library may have them. 1. Citrus: Complete Guide to Selecting & Growing More Than 100 Varieties for California, Arizona, Texas, The Gulf Coast and Florida by Lance Walheim 2. Citrus: Selection Guide, Planting & Care by Sunset Books According to the chart in Walheim's book, grapefruits ripen from Nov thru Aug. Sweet oranges have a wide ranging ripening season - it depends on the variety. For example, Valencia oranges have a long season from Dec thru Sep.
Citrus generally mature during the winter months. The exact time depends on the variety you are growing AND THE LOCATION that the tree is growing in. A citrus variety that matures at a specific time in California, might not be the same time in Florida, and will be a different time in your area. - Millet