From the Archives
of the Rare Fruit Council of Australia
by John Marshall
Irregular
Flowering in Lychees
Scientific
name: Litchi
chinensis
Family:
Sapindaceae
This
is a complex problem in lychees, particularly when they are being grown
away from their natural climate; especially in warmer climates.
The Chinese consider there are two different types of lychee
originating in South China.
(1)
The 'Hill Lychee' from South Kwangtung and Hainan Island, which flowers
and fruits early and requires dry autumn weather and winter
temperatures as low as 15°C or less for good flowering. e.g. Tai So
and Sum Yee Hong.
(2) The 'Water Lychee' from further north
around Canton, which flowers and fruits later (4 to 8 weeks) and
requires dry autumn weather and winter temperatures as low as 10°C
or less for good flowering. e.g. No Mai Chee and Wai Chee.
These two
groups further divide into early, mid and late season ripening,
depending on the time from anthesis to fruit maturity for the
particular variety, and also on the date of onset of winter.
The
'Hill' type could be considered more 'tropical' as it originates in the
tropical zone below the Tropic of Cancer. The 'Water' type on the other
hand could be considered more temperate as it originates further north
above the Tropic of Cancer in the temperate zone.
From
experience in North Queensland, it would appear the tropical types
flower well in the colder climates but the temperate types flower quite
irregularly in warmer climates. The 'Hill' type are reported by Groff
to be planted mostly in fine sandy loam on the Southern foothills. This
type of soil dries out earlier, and in the warmer climate, the trees
flower earlier. The 'Water' type however grows mostly on heavy delta
soil (mud deposited by river flooding). This type of soil takes longer
to dry out and in the cooler climate the trees tend to flower later (4
to 8 weeks).
Reports from China of some varieties tending to
fruit only in alternate years is probably because they are being grown
away from their best natural climate. In fact Groff describes one
'Hill' plantation consisting of Tai So (Hill type) interplanted with No
Mai Chee (Water type), which obviously would result in the No Mai Chee
tending to bear irregularly.
This problem is more evident in
North Queensland where temperatures often don't go low enough for good
flowering, especially for the 'Water type' which require temperatures
of 10°C or less.
A confusing point arises when some trees
vegetatively flush too close to flowering time. Not all branches will
flush and those that don't, flower normally. The others will tend to
flower over an extended period as they harden in the colder winter
temperatures, and a normally early variety may then appear to be a
later variety. First flowering usually occurs in North Queensland in
early winter.
For good, regular flowering in Lychees it seems
they require correct fertilizer and water timing, vigorous summer
growth, autumn dormancy, and winter temperatures as low as 15°C or
less for the more tropical varieties. and 10°C or less for the more
temperate varieties.
Order
of Harvest
The earlier varieties are considered to be more tropical.
| Sum
Yee Hong |
| Souey
Tung |
| Bah
Lup |
| Fay
Zee Siu |
| Tai
So |
| Kwai
Mai Pink |
| Haak
Yip |
| Kwa
Lok |
| Chong
Yun Hong |
| Tim
Naan |
| Sai
Kok Zee |
| Heong
Lai |
| Kwai
Ma (red) |
| No
Mai Chee (standard) |
| Seong
Sue Wai |
| Ah
Neong Hai |
| Soot
Wai Zee |
| Wai
Chee |
Further information has been collected which should contribute towards
better understanding of this problem.
In
the Cairns area of North Queensland last year, record low winter
temperatures were experienced and yet a considerable number of lychee
plantations had poor flowering and even poorer resulting crops. These
two facts appear to be a little contradictory until one looks closer at
the figures. The average low temperature for June 1984 was 17.2°C
with resulting poor flowering, while the average for June 1985 was
15.8°C with resulting heavy flowering.
Another confusing
fact has shown up. Two lychee plantations in this same area had their
usual heavy crop in 1984 when most others failed. Both these
plantations were heavily fertilised immediately after the previous
crop. This result would tend to show that nutrient and carbohydrate
levels are just as important as low winter temperatures. The variety in
question was Tai So. Another small Tai So planting 200 miles north of
Cairns was also reported to have fruited well in 1984.
The old
theory on floral initiation being dependent on the carbohydrate to
nitrogen ratio has been researched for over 60 years but little
positive results have ever emerged. Modern research tends to
concentrate on nutrient levels as well as high carbohydrate levels, for
good flowering. I believe that even with these two levels sufficiently
high, the trees appear to need a triggering factor to actually start
the floral emergence. In early-bearing lychees, the trigger appears to
be the first cold snap of winter. Late-bearing lychees appear to need a
longer dormant period to build up carbohydrate levels and so flowers
emerge later in winter.
If the triggering theory is correct one
wonders what the trigger would be in S.E. Asia where there is little
temperature change throughout the year. From scant information gathered
on mangosteen, rambutan and durian, the trigger appears to be the first
rain after the annual dry season.
It seems that nutrient build
up slows down considerably when the soil is dry or when the soil is low
in nutrients, whereas carbohydrates continue to build up all through
the year.
In
lychee, a heavy crop depletes the nutrient/carbohydrate levels
considerably and the trees have a relatively short time to recover;
about 6 months from December to June for Tai So variety in North
Queensland. In this time, the trees have to replenish their nutrients,
complete one or two flushes, harden off and settle down to a dormant
period in which to build up carbohydrate levels before flowering again
in June or July. Little wonder that if fertilizer timing and weather
conditions are not quite right, the trees could easily miss flowering
in some years.Further information has been collected which should
contribute towards better understanding of this problem.
In the
Cairns area of North Queensland last year, record low winter
temperatures were experienced and yet a considerable number of lychee
plantations had poor flowering and even poorer resulting crops. These
two facts appear to be a little contradictory until one looks closer at
the figures. The average low temperature for June 1984 was 17.2°C
with resulting poor flowering, while the average for June 1985 was
15.8°C with resulting heavy flowering.
Another confusing
fact has shown up. Two lychee plantations in this same area had their
usual heavy crop in 1984 when most others failed. Both these
plantations were heavily fertilised immediately after the previous
crop. This result would tend to show that nutrient and carbohydrate
levels are just as important as low winter temperatures. The variety in
question was Tai So. Another small Tai So planting 200 miles north of
Cairns was also reported to have fruited well in 1984.
The old
theory on floral initiation being dependent on the carbohydrate to
nitrogen ratio has been researched for over 60 years but little
positive results have ever emerged. Modern research tends to
concentrate on nutrient levels as well as high carbohydrate levels, for
good flowering. I believe that even with these two levels sufficiently
high, the trees appear to need a triggering factor to actually start
the floral emergence. In early-bearing lychees, the trigger appears to
be the first cold snap of winter. Late-bearing lychees appear to need a
longer dormant period to build up carbohydrate levels and so flowers
emerge later in winter.
If the triggering theory is correct one
wonders what the trigger would be in S.E. Asia where there is little
temperature change throughout the year. From scant information gathered
on mangosteen, rambutan and durian, the trigger appears to be the first
rain after the annual dry season.
It seems that nutrient build
up slows down considerably when the soil is dry or when the soil is low
in nutrients, whereas carbohydrates continue to build up all through
the year.
In lychee, a heavy crop depletes the
nutrient/carbohydrate levels considerably and the trees have a
relatively short time to recover; about 6 months from December to June
for Tai So variety in North Queensland. In this time, the trees have to
replenish their nutrients, complete one or two flushes, harden off and
settle down to a dormant period in which to build up carbohydrate
levels before flowering again in June or July. Little wonder that if
fertilizer timing and weather conditions are not quite right, the trees
could easily miss flowering in some years.
The Bengal variety is
notoriously regular in its alternate year bearing in North Queensland.
A small group of lychee trees in Singapore have been reported to fruit
only about every ten years. A Wai Chee tree in Cairns which is never
fertilized has fruited only three times in the last 45 years. This is a
cold weather or late variety growing in a tropical area (Cairns is
17° south latitude)
For regular flowering, it is important
that lychees be planted in a climate where winter temperatures are low
enough to suit the particular variety. Another important point is that
lychees be fertilised heavily immediately following harvest.
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