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Flowering Habits of Hardy Waterlilies
in the Tropics

Story and Photos by Pairat Songpanich, Thailand
Edited and Translated by Dr. Slearmlarp Wasuwat, Thailand

The hardy waterlily is a perennial crop originating in temperate and cold climate zones. However, when grown in the tropics, it adapts itself remarkably. Some grow and bloom all year round. Some may rest a very short period if the weather is extremely cold. Others may continue their growth but produce only very few flowers. 

Information shown here reports results of flowering habits of 21 well-known hardy waterlily cultivars grown for three years from 1 December 2000 to 31 December 2003. A rhizome of each cultivar was planted in 46 x 16 cm. (18.1 x 6.3 inch) width and height plastic container filled up with a mixture of paddy clay soil, 2 handfuls of dried cow manure and 2 table spoonfuls of 14-14-14 slow release fertilizer. Each container was put in a 65 x 45 cm. (25.6 x 17.7 inch) width and height cement jar placed in an area to gain full sun during 07.00-17.00 hours.

Maintenance and care were done by keeping the jars filled with water at all times. The whole pedicle and peduncle of old leaves and faded blooms were pinched off. Chemical fertilizer 16-16-16 and 8-24-24, one teaspoonful of each were applied alternately every two weeks for three months, then increased to one and a half spoonfuls of each formula afterward.

Each cultivar was allowed to produce only three shoots. Numbers of bloom produced each month were recorded on a plastic label sticker attached at the jar (see Figure 1).

The studies were located at Nonthaburi Province, Thailand, at latitude 13° 51' 40" North and longitude 100° 31' 35" East. 

Figure 1. Labeling and recording sticker of Nymphaea 'Gloriosa'

Numbers of bloom of each month of each year and of three years were added and averaged for each month of one year. Results included a hole year average are presented in Table 1.

Table 1. A annual average of bloom numbers of 21 hardy waterlily cultivars

< Nymphaea 'Gloriosa'

Graphic illustration in Figure 2 demonstrates an outstanding performance in flowering by Nymphaea 'Gloriosa' at 163 blooms per year. Next were N. 'Charles de Meurville', N. 'Sirius' and N. 'Peachglow' produced 127, 116 and 114 blooms respectively. The lowest were N. 'Perry's Fire Opal', N. 'Sanguinea', N. 'Sunrise', N. 'Gonnère', N. 'Yuh Ling', and N. 'Colorado' which bloomed 28, 28, 30, 33 and 36 respectively. It should be noted here that N. 'Gloriosa' produced flowers nine times more than N. 'Perry's Fire Opal'.

Average number of flowers produced by 21 cultivars was 73 blooms/cultivar/year. Nine cultivars produced blooms at higher than average value; the other 12 cultivars were lower.

< N. 'Perry's Fire Opal'

Figure 2. One year flowering performance of hardy waterlily in the tropics

Graphic illustration in Figure 3 shows that the pattern of flower production of all cultivars varied in similar directions. Each year and on the average, flower production was only a little early in the year and gradually increased until April. They increased slightly during April and May, then increased to their peak in July. The flowering then gradually dropped to their lowest at the end of the year.  

Figure 3. Flower production in 2001-2003 and their averages

Graphics presented in Figure 4 indicate a positive correlation of flowering production and day length (number of hours between sunrise and sunset). Even though the latitude at the studied location area was 13° 51' 40" North, the longest day in June was 12.80 hours and the shortest day length in December was 11.20 hours. The difference was only 1.60 hours. Note the highest flower production of 266 in July compared to the lowest of 18 flowers in January. Both results were about one month after the highest and lowest of day length peak. It can be confirmed that day length is one of the major factors influencing flowering production of hardy waterlilies when grown in the tropics.   

 Figure 4. Correlation of day length and flower production of hardy waterlilies in the tropics

Looking back at Table 1, one may notice some cultivars were very sensitive, some partially sensitive to short day length.

1. Very sensitive to short day length at the early and the end of the year such as N. 'Gonnère', N. 'Perry's Fire Opal', N. 'Pink Sensation, and N. 'Sirius'
2. Partially sensitive such as N. 'Gloriosa', N. 'Gypsy' and N. 'Colorado'

Temperature was the second factor affecting flowering of hardy waterlilies, next to day length. Extreme hot or cold climate would reduce flower production.

The monthly temperature averages over three years during the studies and average of monthly flowering in Figure 5 shows the influence of temperature. Rate of flower production was reduced for one to two months from May to June after very hot temperatures in April. Also, flowers were few, even more so, during very cold [for Thailand] weather in December and January. Some cultivars rested and dropped their floating leaves. Thus, one can conclude that day length and temperature are two factors influencing flower production of hardy waterlilies grown in the tropics. 

Figure 5. Influence of temperature on flowering of hardy waterlilies grown in the tropics

There were no outstanding effects of daily duration of sunlight (Figure 6), and relative humidity (Figure 7). 

Figure 6. Relation of sunlight and flowering of hardy waterlilies in the tropics

Figure 7. Relation of relative humidity and flowering of hardy waterlilies in the tropics


Besides good care and maintenance of hardy waterlilies in a tropical climate, for best production of flowers, day length and temperature are two major factors. Long day length increases flowering and vise-versa. Cold climate that affects growth of most plants makes a more pronounced effect on hardy waterlilies when grown in tropical areas. 

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