Grapefruit (Citrus x paradisi) is a subtropical tree that is winter hardy in U.S. Department of Agriculture plant hardiness zones 9 to 11 and is grown commercially in Florida, California, Arizona and Texas. Its large fruit is slow to mature, and it can be allowed to mature on the tree for several months.
Young grapefruit trees typically begin producing fruit in the third year after they're transplanted, and they will continue to produce each year thereafter. The length of time between the trees' flowering and the maturity of their fruit depends on climate; in very warm climates, the fruit may mature in as little as seven or eight months, but in cooler climates, it may take as long as 13 months.
Legal standards for commercial growers set very specific guidelines, based on the amount of soluble solids in the fruits' juice, for when grapefruit can be considered mature. In Florida, fruit typically reaches legal maturity in September or October, and in Texas the legal standard is usually reached sometime in mid- or late October.
At legal maturity, a grapefruit's peel is usually still predominantly green, although pink varieties such as 'Ruby Red' may begin to show a red blush. Over two months or so after legal maturity, the fruits' peels gradually transition from green to yellow.
On-Tree Storing and Ripening
If left on the tree, grapefruit will continue to mature, increasing in size and sweetness as they age, and the fruit can be essentially stored on the tree for harvest any time between October and May.
The best time to harvest the fruit is after about 50 percent of the peel has begun to turn yellow. Some pink-fleshed varieties will begin to lose their interior color if left on the tree too long; 'Ruby Red," for example, begins to lose color after the beginning of January, and 'Henderson' loses color after the end of February or the beginning of March.
By the end of May, the fruit will begin to fall from the tree, and seeds inside the fruit may begin to germinate.
To harvest mature fruits, pull down and twist so that the stem breaks away from the branch and remains attached to the fruit. Do not shake the tree to make fruit drop because the flesh is easily bruised and can be damaged on impact with the ground.
After harvesting, grapefruit can be stored for two to three weeks in the fresh produce compartment in your refrigerator.