North American Fruit Explorers mailing list at ibiblio

[claude sweet <sweetent@home.com>]

The discussion of growing tropicals should include a discussion of just
what is a tropical fruit.

In my experience a tropical fruit prefers a rather narrow temperature
range with a limited tolerance to cool temperatures and almost no
tolerance to freezing temperatures. Tropicals do not have a winter
chilling requirement.

A banana, pineapple, passion fruit, tamarillo, papaya, and guava would
be excellent examples of a tropical fruiting plant.

Subtropical have more tolerance to both high and lower than ideal
growing temperatures. Brief exposure to freezing temperatures is
tolerated provided the plant in not in active growth. Winter chilling
requirements are generally quite low. The date palm needs a long hot,
dry summer to mature high quality fruit. High humidity can cause the
fruit quality to be adversely affected, thus it is not grown commercial
in the USA except for desert regions in California (Indio and Palm
Spring). Cold temperatures at the base of the palm tree does not seem to
affect the tree in the winter. The palm also has amazing salt tolerance.
The mangoes grown in California backyards can be grown in frost free
winter climates that experience only occasional light frosts. Their
major problem in coastal areas is the plant and fruit susceptibility to
mildew.

Feijoa, fig, oriental persimmon, the commercial kiwifruit species,
citrus. loquat, cherimoya, and macadamia nuts are excellent examples of
subtropical plants. Fig and kiwifruit are much hardier in their dormant
period, but the kiwifruit is very subject to frost injury from a late
spring frost. As the kiwifruit requires a long growing season, the fruit
may be damaged by an early fall frost in colder climates. The cherimoya
has its brief dormant period in the late spring when their is no danger
from frost, but as the fruit ripen in the winter, the fruit and tree is
very subject to damage from freezing temperatures. 

I would classify Asian pears as a temperate fruit that requires winter
chilling to achieve best results. I have several for cross pollination,
but fruit set is very poor even through the trees don't exhibit any
delayed foliation that is typical of high winter chilling cultivars of
temperate fruits grown in a low chill area.

The avocados grown commercially in California vary according to their
cold tolerance. They don't seem to have any winter chilling requirement.
The citrus grown in California prefer hot summers and many require
specific exposures to cool temperatures for the winter fruiting
selections to develop fruit coloration. Some citrus require a large
number of heat units for the fruit pulp to color and achieve the desired
levels of sugar. This is especially a problem in grapefruit with
red/pink flesh.

Growing and fruiting the plants I have mentioned require different
approaches to get them to flower and achieving pollination can be
another problem if required.

Growing trees in containers for extended periods of time to achieve
fruiting size is also a challenge.

Claude Sweet
San Diego, CA

 

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