induces more profuse flowering. It is not known if this response to fire is caused by the temporarily increased soil temperature or higher temperature of the soil for a much longer period of time resulting from the removal of competing plant cover, allowing the sun to shine directly on the soil; or to nutrients released to the soil by the burning of surface vegetation. It does not seem likely that soil temperatures would be much affected at the depths that some of the tubers are found. Another idea that has been advanced is that ethylene produced during burning promotes flowering. Ethylene does induce flowering in such plants as pineapples.
Tuberous Drosera have long been considered the most difficult plants of the Sundew group to grow in culture. This unwarranted reputation is attributable to the inadequacy of good cultural information until recently. The want of good information in the past prevented growers from providing the necessary and correct environment for successful growth. The most common outcome with tuberous Drosera in culture was a continuing decrease in tuber size with each succeeding year until the plant simply died of starvation.
In their native habitat, tuberous Drosera experience a 6-month growing season, during the Australian winter season, when the temperature ranges from 35-79°F (2-26°C) accompanied by 15-22 in. (38-56 cm) of rain. During the Australian summer the plants must endure a 6-month drought relieved only by an occasional thundershower, with temperatures ranging from 70-100°F (21-38°C). During this season the aboveground portions of the plants die back. The below-ground tuber, with its stored food, will resume growth upon the arrival of the wet season.
The problem experienced when growing tuberous Drosera in cultivation turned out to be the lack of attention to the plants' natural requirement for 6 months of vigorous growth in temperate, moist conditions. Instead growers, following customary practice, allowed the plants only about 3 bountiful months. As a consequence of the short growing season furnished the plants, the tubers could not store enough carbohydrates to form a tuber as large or larger than the original. Thus each year the tuber produced shrank, resulting in smaller and weaker plants the following year. When provided constant environmental conditions so the plants grow for about 6 months, the tubers and plants become larger each year until their mature size is reached. Upon reaching mature size they maintain their size and also produce the axillary tubers utilized for natural asexual reproduction. In short, the key to successfully growing tuberous Drosera is the provision of a sufficiently long growing season, accompanied by strong light with an adequate photoperiod, so that the plants can make and store food reserves to insure vigorous future growth.
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