Should you plant your tomato rows oriented north to south or east to west?

Proper vegetable garden orientation will assure that your plants are positioned in the best way to achieve optimal yield. Conventional wisdom is that garden rows in the Northern hemisphere should be oriented north to south so that the plants receive the same amount of sunshine during the d

Maarten van der Meer, a PhD student studying horticulture and product physiology at Wageningen University, led a study of how row orientation affected the yield of hedgerow tomato crops. The work was recently published by in silico Plants. Tomatoes were planted in double rows so that plants in rows oriented north to south (N/S) were facing east or west and those in the east to west rows were facing north or south.

The authors measured the growth, architecture, photosynthesis, and fruit dry mass (i.e. yield) of the plants of both rows in the north-south and east-west row orientations.

They found that conventional wisdom, in this case, was wrong: there was no difference in yield found between rows oriented north to south compared to those oriented east to west.

However, the authors did find a difference between east- and west-facing rows oriented north to south. Although south -facing rows had lower leaf area, they had 7% higher ripe fruit dry weight than north-facing rows.

The authors adapted an existing tomato functional- structural plant model to uncover why. The model was developed on the GroIMP platform (Kniemeyer 2008) and consists of an architectural, photosynthesis and light module.

The model simulations showed a 7% higher light absorption for the south-facing rows than north-facing rows. More light generally equates to higher levels of photosynthesis. However, as the light intensity increases, the photosynthetic rate eventually reaches a maximum point– this is called light saturation. Above this point, additional light does not contribute to photosynthesis.

This is what the authors found: photosynthesis of the south-facing rows was 4% lower than north-facing rows due to local light saturation.

The authors then simulated what effect an equal leaf area between the rows would have had on light absorption and photosynthesis. If leaf area were equal, the light absorption for the south-facing rows would be 19% higher and net photosynthesis 8% higher than for north-facing rows.

“This result demonstrates that plants can adapt their morphology such that differences in light absorption and photosynthesis between north- and south-facing rows are minimal,” according to van der Meer.

If the south facing rows had lower photosynthesis, why was there more fruit?

The authors speculate that this could be due to a higher fruit temperature in the south-facing rows,  resulting in a higher fraction of assimilates partitioned to the fruits..

So, should you plant your tomato rows oriented north to south or east to west?

van der Meer weighs in on this. “What isn’t considered in conventional wisdom is that plants can – and do – adapt their leaf area in response to light and shading, which results in more uniform light absorption and therefore photosynthesis. Additionally, plants do not necessarily use all of the light they absorb for photosynthesis. As we saw with the south facing rows, exceeding light saturation levels levels did not result in an increase in photosynthesis.”

RESEARCH ARTICLE:

Maarten van der Meer, Pieter H B de Visser, Ep Heuvelink, Leo F M Marcelis, Row orientation affects the uniformity of light absorption, but hardly affects crop photosynthesis in hedgerow tomato crops, in silico Plants, Volume 3, Issue 2, 2021, diab025, https://doi.org/10.1093/insilicoplants/diab025