Greenhouse Canada

Inside View: July 2019

How many friends do your plants have?

June 12, 2019  By Gary Jones

Cast your eyes over articles that discuss rootzone management and conversation is usually focused on a number of issues around soil or nutrient solution chemistry (pH, EC, specific nutrients, dissolved oxygen) or physical properties (e.g. water availability, irrigation strategies, media saturation and air filled porosity). Obviously, these are all key factors that need careful attention, particularly in hydroponic systems.

But, unless we’re discussing a particular root disease, it strikes me that we don’t often consider the topic of rootzone biology. I guess it’s harder to see or measure, and it’s therefore easier to concentrate on characteristics that can be managed through data collection. It’s often said that ‘you can’t manage what you can’t measure’. And soil biology is probably quite hard to measure.

Some years ago (more than I care to remember actually), work was done at Stockbridge House Experimental Station (now Stockbridge Technology Centre) in Yorkshire, England, looking at efficacy of disinfection techniques for re-circulating hydroponic nutrient solution in rockwool-grown cucumbers. The trial set out to investigate the potential risk from particular root disease organisms, the assumption being that since the solution was re-circulating, then infecting plants in one area of the greenhouse would lead to widespread and rapid infection of plants throughout the entire crop. However, it turned out that while fungal infections did spread, the rate seemed to be at a much lower rate than expected. Delving further into what was happening, a number of beneficial organisms were found in the rootzone, helping to slow down the spread of pathogens. However, it is difficult to measure those same beneficial organisms in a commercial setting which doesn’t have laboratory equipment and procedures.


Imagine for a moment then, if we could insert a cheap and reliable probe into our rockwool slabs, coir bags, hanging baskets or plant pots to give us real-time measurement of the number of beneficial organisms present. Or the population and diversity of plant pathogens. Or perhaps the actual distribution of mycorrhizae or bacteria that could help a plant thrive. Once we’re able to easily, affordably and reliably measure such factors, then we could start to manage them for the benefit of our crops.

And there may be more. In his book ‘The Hidden Life of Trees’, Peter Wohlleben describes the friendship of trees with one another, to the extent that he believes stumps of otherwise seemingly dead trees can be kept alive by supplies of sugar from neighbouring (actively growing) trees. This “assistance may either be delivered remotely by fungal networks around tree root tips – which facilitate nutrient exchange between trees2 – or the roots themselves may be interconnected.3” Wohlleben has other examples of where “healthy neighbouring pines must have been helping their dying comrades by supplying their roots with food” and he proposes that “nutrient exchange and helping neighbours in times of need is the rule” rather than the exception. Further, he states that “you find twice the amount of life-giving nitrogen and phosphorus in plants that cooperate with fungal partners than in plants that tap into the soil with their roots alone”.1

OK, so trees do have one very significant advantage over our production crops in building these ‘friendships’. We all know that getting to know someone takes time. Growing through a complete crop cycle in no more than (typically) one year, our greenhouse crops aren’t blessed with an abundance of time to build these relationships. All the more reason then for us to learn about them, nurture them and build them into being an integral part of our everyday rootzone management. Ponder this next time you reach out for your pH / EC probe.

  1. Wohlleben, Peter (2015) “The Hidden Life of Trees”. Greystone Books Ltd.
  2. Fraser, E.C. et al (2006) “Carbohydrate transfer through root grafts” in Tree Physiology, vol 26, quoted in Wohlleben.
  3. Maffei, Massimo, quoted in “The Silent Scream”, MaxPlanckResearch 4 (2007) 65 (referenced in Wohlleben).

Gary Jones is co-chair of Horticulture at Kwantlen Polytechnic University, Langley, BC. He sits on several industry committees and welcomes comments at

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