Lemons (Citrus limonia) are the most popular acid citrus for cooling drinks and cookery. Although the tree is less attractive than most other citrus species, the value of the fruit goes far to alleviating this deficiency.
Lemon varieties are fewer in number than for most popular citrus fruits and among the tree a lemon there is little difference in fruit characteristics.
`Eureka’ is of typical “lemon” shape—elliptical, with a nipple at the blossom end and amore or less necked stem end. The tree is the smallest of the Lemon varieties, more open, spreading, and with nearly thornless shoots. In Calif. ‘Eureka’ is preferred in the cool coastal districts because more of its fruit ripen in the late spring and early summer.
‘Lisbon’ is the variety preferred in the Calif. lemon districts having higher summer temperatures, again because under these conditions a higher percentage of the fruit ripens at a favorable time. The tree is substantially larger, more upright, denser and more vigorous than other Lemon varieties, and with thorny shoots.
‘Villafrartea’ is a variety quite similar to ‘Eureka’ in fruit, but more like ‘Lisbon’ in tree characters. In Calif. this variety tends to produce a higher percentage of its fruit in the fall and winter, an undesirable characteristic which has limited its use. However, it is the best adapted of the true lemons to the warm, humid Southeast.
‘Meyer’ (Meyer Lemon) is an anomalous kind, possibly a hybrid bearing acid fruits of lemon character. The fruit is nearly round, with a short nipple. It has a light orange color rather than yellow, with very juicy light orange-yellow flesh rather than the pale greenish-yellow of the true lemons. The tree is dwarf, and much more cold-resistant than the true lemons, which makes it a garden favorite.
‘Ponderosa’ (American Wonder) is mentioned primarily for its very large fruit; both tree and fruit have ornamental value, but the fruit is of poor quality for food use.
In regions where lemons are not well adapted the Rough Lemon and the Calamondin (C. mitis) are sometimes used as substitutes, as both yield fruit with acid, plentiful juice. Rough Lemon, as its name implies, bears a roughish orange-yellow fruit of small orange size. Calamondin fruit is quite small, round and yellow; this species is sometimes used as an ornamental garden plant.
‘Millsweet’ and ‘Dorshapo’ are 2 sweet lemons (low acid); both are believed by some to be hybrid sorts, although their fruits are quite lemonish in appearance. ‘Millsweet’ is nearly round in shape, while ‘Dorshar’ resembles ‘Eureka’ in fruit. They are generally considered to be novelty fruits, but may have value for those who object to the highly acid citrus.
The true lemons are less cold-hardy oranges, but slightly hardier than limes. Some tree damage will occur when temperatures drop below 24° or 25° F., and defoliation at somewhat higher temperatures. They are also slightly tenderer than are orange fruits. The ‘Meyer’, on the other hand, is fully as hardy as is the Orange will be recognized that protection against will be more difficult for lemons.
Lemons are propagated by the same methods as given for Oranges. Rootstocks commonly used are the same as for Orange, except that Lemon tends to overgrow Sour Orange stocks, and to be relatively weak on them. Sweet Orange, Citrange and Trifoliate are possibly a little better.
Size differences among Lemon varieties and kinds result in a variety of recommended planting distances, which also can be varied byte training given. The vigorous true lemons, as ‘Lisbon’ and ‘Villafranca’, make large trees on good rootstocks if allowed to grow freely.
Trela require 24 to 30 ft. spacing; with heavy pruning they may be kept somewhat smaller. ‘Eureka’ is often kept low by heavy pruning, and can be maintained easily at 18 to 20 ft. spacing. ‘Meyer’, being semi-dwarf naturally, needs about 8 to 12 ft. spacing. Rough Lemon and the sweet lemons would need the same spacing as for ‘Lisbon'; the Calamondin is often kept small by treating it as a small ornamental shrub; its natural tendency is to make a rather tall but narrow, cylindrical tree. The effects of closer planting and shaping are the same as described for Orange; also by using dwarfing trifoliate stock, space requirements may be materially reduced.
Lemons are pruned more heavily than any other citrus species; rather than a requirement this is probably dictated by the need to keep trees small for the continual harvest. Nevertheless, it is true that lemons fruit much better than other citrus under such heavy pruning, which may therefore be used to control tree size. Lemons tend to throw strong, upright water-sprouts which, if not removed, soon make an impenetrable thicket of the center of the tree, and tend to shade out the productive portions of the tree. Some of these water sprouts may be converted to fruiting wood by pulling them to the outside of the tree, in a nearly horizontal attitude, but generally they are removed. ‘Eureka’ can be kept quite low and spreading; ‘Lisbon’ and ‘Villafranca’ somewhat more upright. ‘Meyer’ needs practically no pruning except the removal of interfering branches. Cultural needs and practices are otherwise very similar to those for the Orange.
Commercial lemons arc harvested according to size, without regard to color development. Green fruit may be ripened artificially with ethylene or be stored, where it develops its full color. The gardener can profit by this experience, for it is not necessary to await color development to use the fruit; when it is of typical size and is juicy it is ready for use. However, for appearance most fruit will probably be picked as it reaches full yellow color; large fruits on vigorous trees may actually be past their prime by that time. Lemons should be clipped from the tree, and when properly handled they have a very long storage life, although this is less important to the gardener considering the overbearing habit of the species. For storage the fruit should be washed, well cured, and held at refrigerator temperatures. Under close commercial control lemons are sometimes stored for 6 months or more. The skin becomes thinner and may even appear and feel dry but the fruit retains its juicy condition.
The ‘Meyer’ does not have as long a storage life, but holds its fruit on the tree over a rather extended period. Like the true lemons they may be used from the time they are juicy to the end of their on-tree life. Rough Lemon and Calamondin will be used from the tree.
The pests and diseases of the lemons are the same as for Orange. Lemons are more susceptible to scab and other fungus diseases than most citrus in the warm, humid Southeast. Under adverse conditions lemons also tend to defoliate rather readily; the tree is, therefore, often less attractive than are other citrus.