From the Archives of the Rare Fruit Council of Australia, inc.
by John Marshall


Seasons in Australia are opposite to those in the US.  Summer is Dec. Jan. Feb. Autumn is Mar. Apr. May. Winter is June July Aug. Spring is Sept. Oct. Nov.

Irregular Flowering in Lychees

Litchi chinensis
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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Bibliography

Marshall, John. "Irregular Flowering in Lychees." rfcarchives.org.au. Archives of the Rare Fruit Council of Australia. July, Sept. 1985. Web. 28 Mar. 2015.

Published 28 Mar. 2015 LR
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