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Time to reboot your root zone in Inside View: July 2016

Time to Reboot Your Root Zone

June 8, 2016  By Gary Jones

Root zone management. Hmmm. Quick “Google” to see what’s out there. Oh. Apparently, the “Internet Assigned Numbers Authority (IANA) is responsible for management of the DNS [Domain Name System] root zone. This role means assigning the operators of top-level domains, such as ‘.uk’ and ‘.com,’ and maintaining their technical and administrative details.”1 So, root zone management is a bigger topic than first thought!

Who knew?

Following the computer theme, these comments are also high up there (first page of results) in the web search:

  • “Internet Activity Depends on Proper Root Zone Management.”2
  • “Root Zone refers to the highest level of the Domain Name System (DNS) structure.”3

Clearly, computer techies are taking their lead from our green industry. Firstly, we all know that plant (or Internet) activity is fundamentally
dependent on optimum root zone activity. Poor roots lead to poor plant growth. Simple.

Secondly, as in the computer world, the root zone could well be the highest level of the plant system, since without it there is no plant. OK, so we agree the root zone is critical to the success of plants (and the “www”).

But what exactly is the root zone?

Most simply put, the root zone is “the part of the plant that is below the soil and the area surrounding it.”4 But for tree people, it is more complicated than that. “A tree’s critical root zone (CRZ), sometimes also called the root protection zone (RPZ), is defined as a circle on the ground corresponding to the drip-line of the tree.”5 There are simple mathematical ways (using radius of tree stem) to calculate (and hence define) what that drip line looks like.

Arborists spend much of their time and
resources managing what is going on underground, and you will hear them talking of “root zone pruning,” “air knives” and “root control barriers” to stop things getting out of hand.

Of course, we use root zone (air) pruning in other specific areas of horticulture, such as in plant propagation. But we don’t really afford the same degree of physical attention to this critical area of plant growth for the majority of greenhouse crops. While we do occasional inspections of roots (cutting open the grow-bag, tipping a pot upside down), we tend to focus on the health, growth and balance of the visible parts – stems, leaves, flowers and fruit. When, for example, was the last time you did any root pruning in potted crops or greenhouse vegetables? Of course we don’t. But neither do we perhaps pay proper attention to timing of potting-up based on roots rather than tops, or spacing to manage root growth.

Dr. Mohyuddin Mirza’s article “Root Health is Hidden Wealth” (Greenhouse Canada, April 2016, Pgs. 38-42) gave a great summary of the critical components of what greenhouse vegetable growers check to manage root health: drainage from bags, dissolved oxygen levels, EC/pH, media and water temperature, water quality, sodium levels, irrigation schedule and choice of growing medium.

One cannot argue against any of these factors being a crucial element of day-to-day management of root zone. They are all relatively easy to see, can be checked using cheap and simple equipment, and can be built into a daily or weekly schedule for staff to undertake. If you’re not doing these things, perhaps you ought to be.

And admittedly, bedding is such a quick turn-around crop that it’s not going to be worthwhile (or indeed physically practical) to do much with the roots. But for larger, high-value potted crops or long-season crops, is there anything we can apply from what our tree-growing colleagues do to help us better manage the critical root zone of crops?

Perhaps. We’re never too old or too smart to learn.


Gary Jones is co-chair of horticulture at Kwantlen Polytechnic University, Langley, B.C. He serves on several industry committees and welcomes comments at

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