Mexican or true Lime trees (Citrusaurantifolia) are small, slender, often willowy, with numerous thorns, and small leaves. A second group serving the same purpose is the Tahiti Group, which is characterized by larger, less thorny trees, and larger fruit. The ‘Rangpur’ Lime, probably an acid Mandarin Orange, which it resembles in tree and fruit, also serves the same purpose, and is treated here. These very acid citrus are prized primarily for the unique, refreshing flavor of their fruit as used in cooling drinks and cookery.
The true limes will tolerate but a degree or two of frost. Growth is therefore limited to southern Florida, the Keys, warmer areas of the southeast Gulf coast, and to protected sites in the most frost-free areas of southern Calif. Varieties of the Tahitian (Persian) group are only slightly more cold-resistant and can with-stand temperatures of about 26 to 27° F. without serious injury. The ‘Rangpur’ Lime on the other hand is nearly as hardy as the Sweet Orange, and can withstand low temperatures without serious tree damage. All, however, have tender fruit which can withstand but 3-4 degrees below freezing, ‘Rangpur’ fruit being slightly tenderer.
As true limes are propagated mostly by seed, the variety designation has less significance than for many other plant varieties. Accepted fruit type is small, oval to round. The fruit becomes lemon-yellow when fully ripe, but is usually harvested when still green, or showing but a slight yellow blush. The flesh is greenish yellow, tender, and yields abundant, very acid juice with the typical lime flavor. Mexican, West Indian, Key and thornless variants of the above names may be offered by nurserymen in areas where limes are grown.
‘Bearss’ is the best of the Tahiti or Persian group, and may bear the name Tahiti or Persian, but the former is a distinct variety. The fruit is larger than that of the true Lime, being from 1 to over 2 inches in diameter. The skin and flesh color is about the same as for the Mexican group, and the juice has the flavor of the true lime. ‘Bearss’ is seedless.
‘Rangpur’ can be used to extend the range of very acid citrus. The fruit is a deep orange color, the skin loose, and the flesh orange colored, juicy, and with only a slight suggestion of the true lime flavor. In fruit and tree it closely resembles the mandarin oranges, especially the tangerines; the fruit is slightly seedy. A few sweet limes, most nearly resembling the Tahiti Group, are known; varieties are ‘Palestine’, ‘Sweet’, and ‘Otaheite’. The latter, propagated from cuttings, is sold in quantity as a Christmas potted ornamental plant bearing bloom and fruit. All of the sweet limes are suspected hybrids.
Propagation of Limes
Mexican limes are readily propagated by seed, most coming true to type, as they are highly polyembryonic. The ‘Bearss’ must be propagated vegetatively, as it is seedless, and is a triploid citrus. ‘Rangpur’, unlike the Mexican, will not come true from seed in most cases, so to assure getting the desired type, budded trees are best used.
Lime trees may be top worked, but their use as rootstocks has not been generally tested, except that the ‘Rangpur’ is apparently a satisfactory stock for other citrus. The cold-tenderness of the Mexican and Tahitian groups would not suggest their use in areas where these kinds cannot be grown.
Mexican limes can be grown on any of the common citrus rootstocks, but appear to over-grow Sour Orange rootstock badly, suggesting degree of incompatibility. In southern Florida, Rough Lemon has proved to be good; Sweet Orange and Grapefruit rootstocks have been used successfully. Of course most are grown on their own roots, as seedlings. The same root-stocks will serve for varieties of the Tahitian Group or ‘Rangpur.’
Planting a Lime Tree
Mexican limes make small trees, and planting distance need not be in excess of 15 ft.; the Tahitian Group grow considerably larger, and distances of about 22 ft. should be allowed; the same or slightly longer planting distances apply to ‘Rangpur’. Little is known concerning the value of dwarfing rootstocks for the limes; the ‘Otaheite’, as mentioned, is adapted to pot culture, and all could be kept small by growing in small tubs if given good attention.
The Mexican and Tahitian group of limes tend to bloom and mature fruit throughout the year, although there is a normal peak season of maturation. In Calif., Mexican limes ripen most of their crop in the late fall or winter; the ‘Bearss’ somewhat later. In Florida, the main crop ripens from June to Aug. ‘Rangpur’ has but a single bloom and ripening period in the South-west and Pacific regions, but may bear a small number of fruit throughout the year in the Southeast; its normal peak production is in winter and early spring.
Limes may be kept for some time in cool, dry storage if properly cured when harvested. ‘Rangpur’ is not so well adapted to prolonged storage.
Besides the normal diseases of citrus, the Mexican lime is particularly subject to anthracnose fungus, particularly in the humid Southeast—a disease which attacks both fruit and foliage. On the other hand, the Tahitian Group is susceptible to citrus scab, to which the Mexican group is highly resistant, if not immune.
Lime is not necessary for all plants on all soils. In fact, lime is not even necessary as an additive on all soils. Contrary to popular belief it is not a fertilizer but does have an active part to play in garden soils. Lime is calcium carbonate, and of course all plants need calcium in order to grow properly. In soils made from limestone rocks there is usually sufficient present in the soil, or if lime is being leached out by heavy rains, more calcium carbonate becomes available. In acid soils, lime is sometimes needed for certain plants, especially vegetables and farm crops, although most trees and shrubs seem to be unaffected with or with-out it.
A “sour” soil is one with most of the lime leached out. In areas where soils have been made from acid-bearing rocks what little calcium carbonate there is present in the soil is being continually leached out by rainfall. Farmers know that such a soil is unfit for growing clover or would not produce a good crop of vegetables. The gardener should understand the uses of lime in order to use it intelligently and also save him time and money in applying it un-necessarily.
Soil that has a green scum or small amounts of moss in it, is in poor condition, certainly in need of fertilizer and possibly is in need of lime also.
Lime, added to a heavy clay soil, makes it more workable by improving the physical condition. It causes the finer particles of clay and silt to combine (in a heavy clay soil), forming larger particles and thus allowing space for air and water drainage. On the other hand, applied to sandy soils it can prove harmful. It also reduces the amount of acidity in a soil and soils usually need it if the acidity is below 5.5 pH.
There are several types of lime on the market but by far the best for gardeners is ground lime-stone, or better still ground dolomitic limestone because this has, in addition, a small amount of magnesium, an essential element for plant growth and often deficient in many soils.
This material, as well as ground limestone, has the added advantage that it can not be too heavily applied, within reason. When the pH of the soil rises to neutral or slightly alkaline the remaining lime becomes less and less soluble, hence there is not the danger from burning foliage with too heavy an application. Some other forms of lime do not act this way but remain soluble even though the soil alkalinity is being raised, hence if too heavily applied, the alkalinity of the soil continues to rise and shortly phosphorous, magnesium and some of the other minor elements are made unavailable. This of course causes injury to the plants. Also, lime does aid in releasing certain chemicals in the soil.
Limestone. This is simply the ground lime-stone rock and it should be finely ground. It should pass a to-mesh (to the inch) screen and half of it should pass a too-mesh screen.
Oyster shells. These are available only near the seacoast where oyster fisheries are located. They have little value unless finely ground.
Marl. This is sometimes available locally and is a mixture of limestone and silt or clays, but they vary considerably in proportion and if price is not a factor these local marls might be overlooked as suppliers of limestone.
Chalk. A poor form of lime, not used as commonly in this country as it is in England. It has twice the bulk but only one half the value of limestone.
Hydrated lime or slaked lime is the hydroxide of time or burned lime to which water has been added. It is a white powder and is highly caustic and difficult to handle.
Burned lime or quicklime comes in large lumps unfit for the gardener’s purpose, and is the commercial oxide of lime. It is a white powder, caustic and difficult to handle.
Of these, the best for the gardener’s purpose is ground dolomitic limestone, ground limestone or hydrated lime, in that order.
How much to apply—the soil test will show this but the old saying is “a ton of lime per acre” which, broken down for small garden plots, is a lb. per sq. yard of soil. One satisfactory application needs not be repeated for 4-5 years. It should be spread evenly on the surface of prepared garden soil and either watered in or allowed to stand until rain washes it down into the soil. Lime does not move up or laterally very well in the soil, the reason why it should not be plowed in. Nor should it be applied to or with manure for this way it does more harm than good. It should not be mixed with commercial fertilizers.
It is best not to use burned or slaked lime in the garden. Certain woody plants, like lilacs and junipers, apparently grow better in acid soils if lime is added. Many plants are indifferent to it and certainly ericaceous plants need very little if any lime added to a good acid soil in which there is plenty of humus.
Applying lime to lawns has been much over-done. Lime corrects strongly acid soils, adds calcium as a nutrient, increases the availability of other plant nutrients and encourages bio-logical activity. Most grasses grow well on moderately acid soils. Lime encourages weeds and clover; hence if a pure grass lawn is desired lime should only be applied on extremely acid soils at least below a pH 5.5. If lime is to be applied to correct acidity, hydrated lime can be applied at a rate of 35 lbs. per sq. ft. or powdered limestone at a rate of 50 lbs. per sq. ft.
Kentucky bluegrass does not always need lime. It needs a fertile soil and if the soil is fertile it can grow well on limestone soils. The chances are that a complete fertilizer added to the lawn will do more good than an application of lime.