Companion Planting in the Tropics – Vertical Stacking

Sweet potato and katuk (sweet leaf/sayur manis)

We have been playing around with companion planting at Project Canossian. Actually it’s more of stacking plants on top of one another rather than just adjacent. Lots of failures with some successes. It is something we have been experimenting with since our days at Project Green Valley. There are many good reasons why you would want to companion plant by vertical stacking:

  • Better use of sunshine: Here in Singapore 1 degree north of the equator, the sun is overhead throughout the year. As Bill Mollison says, a resource that isn’t properly utilized can become a pollution. Sunshine is photosynthesized by leaves and is turned into a yield (for us or other living things). However, when this strong sunshine falls on the soil many things happen. Soil water evaporates, soil organisms (e.g. earthworms) die from the heat, ambient temperature increases due to radiation. A single layer planting of small vegetables or herbs does not use the sunshine efficiently. Lets talk about planting lettuce as an example: for most of the growing duration, most of the sunshine will fall between the tiny seedlings onto the soil. Even when the lettuces are fully grown and touching one another, the leaves are not able to utilize all that good sunshine. One layer of leaf can only photosynthesize so much sunlight, after which the remaining passes through the leaf. Which is why the best use of sunshine here in our climate is still a forest. Almost all of the solar energy would be extracted as the sunshine passes through the many layers. Nothing much is left by the time it reaches the forest floor.
  • Better use of rainfall: Likewise, we are blessed (or, to poly-tunnel farmers, cursed) with heavy rains throughout the year. The kinetic energy of falling raindrops causes soil compaction and sheet erosion when not absorbed by foliage or mulch. Having more leaves to intercept and direct the water flow down the stems allows the soil to drink more gently. If there are not enough roots in the soil to absorb the rain it flows away, causing leaching of nutrients.
  • Shading out weeds: Nature doesn’t waste. Solar energy that falls on soil will be taken up by weeds. Mulching helps but we have seen weeds here that can penetrate mulch (cardboard or leaves) just to reach for sunlight.

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