Xerophytes win water fights
Plants requiring little moisture are thriving where others are wilting in the summer heat
May is almost at an end. Usually around this time, our friends Bantherng and his wife Phen are busy harvesting lychee in their orchard in Phetchabun. This year, however, not one of their more than 100 trees bore fruit. In fact, not one lychee tree in their district of Nam Nao, some 40km from Nam Nao National Park, had fruit this year.
"Usually around New Year a cold spell descends upon Nam Nao, thus triggering the blooming of lychee and longan," Phen's sister Valai explained. "This year, however, it was hot last New Year, and this summer must be the hottest we have ever had."
When we visited Nam Nao two weeks ago, the day temperature was 30C, too hot for people more used to its cold climate. Nam Nao, the northeasternmost district of Phetchabun province, got its name from near-frozen water during November to January or February in years past. When we visited the place for the first time in October 2002, the night temperatures hovered around 11C; we were told it would go down to around 3C and sometimes near zero during December-January. The water (nam in Thai) was so cold (nao) that the place was named Nam Nao by early settlers.
During our repeated visits over the years, summer was always a pleasant 23-26C during the day, and 20-22C at night. Plants like bromeliads, especially those in the genera Neoregelia and Vriesea, simply loved the variation in day and night temperatures. Those with green leaves when grown in Bangkok's climate took on intense red or variegated colours when moved to Nam Nao.
Yet, although the climate was still cold most months of the year, the temperatures no longer went so low as during our early visits. During the past few years, the climate has been rising continuously, so much that our friend Bantherng's lychee trees have gone unproductive. I am not sure whether this could be attributed to more clearing of land for agriculture and planting of rubber trees, or the continuous increase in population since the road was widened four years ago. As more new houses were built, more vegetation was cleared. Or it could be due to global warming.
Travelling along Highway 21 from Saraburi to Lom Sak in Phetchabun was always a delight because of the magnificent display of colourful bougainvillea flowers in the middle of the road and flowering trees like Cassia fistula, or golden shower, and Delonix regia, or flame tree, on the roadsides. Nowhere else could one see golden shower trees with flowers in varying shades of yellow, from cream and dark yellow to golden, and flame trees in various colours ranging from light orange and bright yellow-orange to scarlet or crimson, than along this highway.
This time around, I did not get to enjoy the flowers. Bougainvilleas thrive on neglect; the less water they get, the more they bloom. They are at their best, therefore, in the summer. But the relentless sun, the heat reflected from the road and the moistureless soil this year were just too much for the plants, especially in Muang Phetchabun. They were bone dry when we passed them by, and only immediate watering or a heavy rain now could bring them back from the point of no return. And as most of the trees had been felled years ago when the road was widened, there were not many flowering trees to enjoy either.
With hot climate comes scarce water, not only in Phetchabun but elsewhere. In Bangkok, I woke up one day to find that the Ficus pumila, or climbing ficus, that covers our wall had become crispy. Another species which thrives on neglect, it is seldom watered but it has survived many summers -- until now.
If this summer's soaring temperatures are a sign of what's in store for us in the coming years, it is advisable to plant drought-resistant species in our gardens. Even if water is readily available in Bangkok at one turn of the tap, we should economise on this precious commodity. This is probably one of the reasons why cacti and succulents are becoming popular once again among plant lovers. Small and requiring only a little space, they do not need much water.
Other drought resistant plants to grow are sansevieria, a genus of 70 species known by their generic name and commonly called snake plant or mother-in-law's tongue (lin mangkorn in Thai). These alone will keep you busy, but there are also many other xerophytes, or plants which thrive with little water, such as those in the genera Agave, Euphorbia, Dracaena and some bromeliads including tillandsias. These alone could fill a huge garden with their many different species.
You can also economise on water by grouping plants of the same watering requirements together. Those that require daily watering should be grouped together and separated from xerophytic plants so that you don't have to water all your plants every day.
When watering, remember that thorough watering twice or three times a week is more beneficial to the plant than watering only the surface of the soil every day. Water as needed, that is, when the top inch of the soil is dry to the touch.