Most people don't realize just how large the citrus family is. What you see in the supermarket is only a small portion of what can be grown. Pummelos, blood oranges, limequats, and myriad mandarin varieties offer exciting new taste experiences and landscape possibilities.
Commercial Citrus Belt
The commercial citrus belt extends roughly from California through Arizona, Texas, along the Gulf Coast, and into Florida; but home growers are not necessarily limited to this area. Small changes in elevation and distance from the coast can make a significant difference in minimum temperatures at a given location. Warm spots around buildings and on hillsides can provide safe growing areas in sections that would not appear suitable from a climate map. The important thing to know is a variety's tolerance to cold, especially the minimum temperature it can tolerate. There are many hardy varieties that can be grown much farther north or inland. If your citrus trees are planted in containers and moved to protected locations during cold weather, you can even grow them in Minnesota or Maine.
Where Citrus Grows
The traditional citrus climate extends from northern California down through southern California and into the low Arizona desert. There is a break in New Mexico, a state that has mostly high elevation with cold winters. Then the citrus belt picks up again in southern Texas and extends along the Gulf Coast and into Florida. Not all types of citrus can be grown in all parts of the citrus belt. Climatic differences within the region markedly affect fruit characteristics and quality. What can be grown in Florida cannot always be grown in California and vice versa. The warm, dry days and cool nights of California develop brightly colored fruit with balanced sugar and acid and thick rinds. The warm, humid days of Florida and the Gulf Coast are usually accompanied by equally warm nights; such even temperatures promote lighter colored fruit without pronounced acidity.
Humidity and Temperature
Humidity and day-to-night temperature fluctuations also influence which varieties are best adapted to an area. Almost all lemons in the supermarket come from western states because in Florida lemons do not develop enough acidity. On the other hand, some types of citrus naturally high in acids, such as many tangelos, are too tart when grown in California. They reach peak quality and sweetness only in Florida or along the Gulf Coast. Citrus types have varying degrees of hardiness, so tolerance to low winter temperatures is often the most important factor in determining which varieties you can grow. The foliage of limes is usually damaged if temperatures fall below 32° F; oranges are damaged at about 26° F to 28° F.
Kumquats and kumquat hybrids can withstand temperatures as low as 18° F, but the ripe fruit is usually less hardy than the foliage. The duration of the cold and the position of the tree in your garden also influence how badly trees are damaged. Each citrus type has a heat requirement that must be met before the fruit will become sweet. Grapefruits need the most heat and only reach peak quality in the California and Arizona deserts, southern Texas, and Florida. Lemons can be grown in cooler climates because they don't need to sweeten.
Citrus Flowering Habits
Citrus trees are evergreen and can have both flowers and fruit at the same time, so they are treated a bit differently than other fruit trees. They store food reserves in their leaves and must therefore be protected from stresses that will cause leaf drop. Although the cycles are not as obvious as the cycles in temperate fruit trees, citrus trees go through different stages throughout the year. When temperatures drop below 56° F, the trees stop growing and go into a semi-dormant state. After a period of such cool weather, they can withstand brief cold snaps much more easily than when they are actively growing. It only takes a few days of warmer temperatures to make them more vulnerable, though. In the spring they have a flush of growth and their major bloom period. Some varieties tend to bloom lightly throughout the year; water shortages or other stresses can trigger a second bloom.