In certain American English speaking areas the word “pomelo” (a fruit with a
large yellow, grapefruit like fruit) is used to describe the grapefruit. The true
pomelo, or shaddock (C. maxima) has pale green or yellow fruit, when ripe, larger
than grapefruit.
Citrus are one of the most difficult fruit trees to cultivate, and they normally need
careful attention if they are to give consistently good yields of fruit.
PLANTING
Propagation: seed is generally not suitable as it contains out-pollinated genes and
so it rarely breeds true. Instead “marcottage” (for limes, and sometimes mandarins
and pomelos), cuttings or graftage is done. Marcottage uses the same principle as
“layering”—soil is tied onto a branch using polythene or sacking, sometimes the
bark is also ringed at this site, which encourages roots to grow.
Grafting onto rootstocks is more common, the rootstock itself being grown
from seed. There are many types of rootstock, listed below, the first three being the
most commonly used: Sour Orange, mainly for lemons and oranges, grown in
medium and heavy soils; the root system is deep and vigorous. Rough Lemon, a
lemon × citron hybrid, has a shallower root system for use in lighter, sandy soils;
used in the Caribbean and tropical America; generally produces poor quality fruit.
Sweet Orange, for rich, well drained soils; susceptible to foot rot; generally
produces lower yields than rough lemon with mandarins and oranges but gives good
fruit quality. Rangpur Lime, easy to transplant; tolerates wet conditions; resistant to
gummosis and tolerant to tristeza virus; used in South America and the Far East.
Mandarins, widely used in Asia; some resistance to tristeza, quite resistant to foot-
rot and gummosis; mainly in humid tropical regions. Trifoliate Orange, the best for
cold conditions; tolerates some waterlogging; resistant to gummosis and tolerant to
tristeza; used in Japan for Satsuma oranges. Citrange, used in cold conditions where
resistance to tristeza is necessary. Grapefruit, not much used, best when used for
other grapefruit and pomelo varieties; not very compatible with oranges. Limes, not
much used, except in Israel and Egypt; tend to develop and mature quickly
producing early fruit but they are short-lived and many are sensitive to foot-rot.
Citropsis, a native citrus in the Congo region of Africa, has potential as a rootstock
due to its high resistance to foot-rot and gummosis.
Soil: citrus species will grow on most soil types provided they are neither saline nor
waterlogged. Optimum pH is 5–7. Magnesium limestone is beneficial if the pH falls
below about 5. Manure and nitrogenous fertilisers are very beneficial. With infertile
soil, limes will sometimes survive where other species fail. All species respond well
to fertilisers and manure—Nitrogen is the most important nutrient; excess Potash
(K) can be harmful.
In poor soils, secondary nutrients such as Sulphur, Calcium and Magnesium and
and K.
some trace elements may need to be applied as well as the major nutrients, N, P