We moved from Bangkok to a small town that is at a higher elevation with cooler and dryer weather. The weather and soil in the area make it amenable to growing grapes and there quite a number of vineyards around. I got the big idea that there might be other exotic-for-Thailand crops that might grow here. In particular, I became interested in trying to grow strawberries.
Some mountainous areas in the north of Thailand near Chiang Mai have success with strawberry cultivation. And only a couple of hours away from us there is an area that also produces strawberries. I managed to find some live plants at a farmers market and decided to give it a try.
I started with ten plants set out in the garden at the end of rainy season. They did pretty well, became quite large and lush and produced some tasty fruit, although the fruit were rather small and there weren’t many of them. Still I was encouraged so I propagated a lot of plants from those first ten, ending up with nearly 100 baby plants that I transferred to the nursery until the garden was ready for them.
The following season I put them in the ground in the garden, spent a lot of time on them, and they seemed to do pretty well. However, the fruit were small and dry in appearance – very few appetizing fruit were produced. It appeared that they were suffering from the heat. So although the weather here is cooler than at lower elevations it is still too warm too much of the time to grow strawberries the conventional way.
I have been studying the problem off and on for some time now. Published research indicates the problem in tropical climates is that the roots are too warm too much of the time. The nights just are not cool enough to cool down the soil. Some interesting research has been done in Japan wherein the plants are planted in raised troughs that have a soil cooling system integrated. The trough is comprised of a burlap sheet slung between to horizontal rods. On top of the burlap is a layer of plastic. Soil is filled on top of the plastic and the strawberry plants are planted in the soil. The burlap hangs over the outside of the horizontal rods and rests in a trough containing water. So what happens is the burlap absorbs the water, becoming wet the entire length of the trough. The under side of the burlap is exposed to the air and through evaporation it is cooled. Being in contact with the plastic and soil, it then cools the soil and plant roots.
It is a simple system to construct and would seem to be effective. There are some difficult to control variables, however. One is that high humidity will greatly diminish the evaporative cooling effect. We have “relatively” low humidity in this area but much of the hot season and rainy season is quite humid, at least for long periods during the day. Another variable is the rate of absorbtion and wicking of water by the burlap sheets. In fact, one study showed that felt type material of a particular thickness was required to achieve even cooling. Otherwise there were dry spots which resulted in local hot spots.
So the passive evaporative cooling trough approach is something that, although tempting to try out, may not be very successful. I’ve also be thinking about hydroponic cultivation of strawberries. I can’t find much written about it, however. There are some successful hydroponic lettuce growers in our area but strawberries are going to be a different challenge. And now I’m looking at an active system with pumps and filters rather than a simple passive system. So cost and maintenance could quickly become prohibitive. This remains a pending project.