Lime and lemon trees are citrus trees best suited to the warmer parts of the subtropics, as frosts cause much more harm than what orange and grapefruit trees tolerate. Limes and lemons grow in a wide range of soil types, as long as they are well-drained. Both trees also are considered by horticulturists as "heavy feeders"--appreciating lots of organic matter and soil nutrients for best growth, flowering and fruiting. They also grow nicely in containers.
"Lime" can refer to either of two different species of tree. One species, Citrus aurantiifolia, is commonly called the Mexican lime, key lime or bartender's lime. Another species, Citrus latifolia, is dubbed the Persian or Tahitian lime tree. The lemon tree is more absolute, as it is known botanically as Citrus limon, a singular species. Within each species of lime or lemon, there may be cultivars that demonstrate a specific growing attribute that gardeners find advantageous. The Rangpur lime is not a true lime, but a hybrid made by crossing a lemon tree with a Mandarin orange according to Roert Lee Riffle, author of "The Tropical Look."
Lime trees have an obscure origin since they have been cultivated for millennia across the Old World. Overall, the two species of lime are regarded as having their start in the vicinity of northern India to Southeast Asia. According to Riffle, Citrus aurantiifolia is likely native to monsoonal southern India, while Citrus latifolia is a hybrid initially made by crossing a citron with Citrus aurantifolia. Learn2Grow's plant database entry comments that the lemon tree's origins are also obscure, but likely in northwestern India. Riffle mentions that there is some discussion on whether the lemon is actually an ancient hybrid between a citron and lime.
Lemons and limes are appropriate to grow outdoors only in U.S. Department of Agriculture Hardiness Zones 9 through 12. They are not true equatorial tropical trees, but adapt to many climates as long as winters are not too cold. Mexican lime does not fair well when temperatures drop below 30 degrees F. Persian lime is a bit more tolerant of frost, but temperatures below 25 degrees can still cause leaf and branch die-back. Lemon trees are best where frosts do not occur but, according to Riffle, will sprout new growth even when temperatures briefly get to 20 to 25 degrees. Cultivars of lime and lemon trees have slightly varying abilities and tolerances to winter cold.
Mexican lime is an evergreen with oval leaves. It naturally grows into a rounded shrub, 15 feet tall and equally as wide, with branches densely lined in leaves. Small spines are found between the leaves on the branches. Persian lime is somewhat like a scraggly large shrub growing 15 to 25 feet tall and wide. It is has diminished numbers of spines on its branches and winged leaf stems in comparison to the Mexican lime. Lemon trees, too, naturally are large shrubs maturing to 20 feet in height and width approximately. Lemon branches are long and scraggly with leaves having winged leaf stems. All of these citrus plants are trained with repeated pruning to become single-trunked trees with an upright, rounded habit more suitable to orchard or backyard garden culture.
Mexican lime trees will produce their slightly fragrant white flowers any time of year, but most often from spring to fall and just after a rainy period. The blossoms are much larger than Persian lime's white flowers that open most heavily in mid- to late winter, although appearing any time of year. Lemon trees bloom intermittently across the year, but perhaps most heavily in spring. Their white flowers are a bit smaller than those of the Mexican lime, but significantly more fragrant.
Mexican lime fruits are small and green with a very sour, acidic flesh, while fruits of Persian lime are much less sour, even sweet in comparison according to Riffle. Limes are green but mature with a hint of yellow-green. Lemon fruits are larger than limes and have a much thicker rind and reliably become pale to canary yellow when ripe.
When compared to lime trees, lemon trees grow much better where the climate provides a warm, dry winter and a warm, not-so-humid summer. Lemon trees will flower and fruit in these areas, just not as abundantly, according to both Riffle and the Learn2Grow plant database. Limes and lemons ripen individually across the calendar year on the tree, not ripening all at once in one season.