UKTC Archive

Re: RE: Watering trees during the establishment phase

Subject: Re: RE: Watering trees during the establishment phase
From: Julian Morris
Date: Feb 11 2020 10:55:52
It's all interesting and useful debate, but this thread has become more about 
when do you know a tree needs watered and less about how much water it needs. 
Perhaps the fundamental question is just that, how much water do trees of 
various sizes need at establishment phase? And therefore, if the weather is 
dry and has been dry for so long that there's no residual water left in the 
soil, and watering is the only water a tree is getting, then the total water 
a tree needs equals the total watering it is to be given (after allowing for 
evaporation and the like). Isn't that the question? The criteria for when 
watering is needed are a different and more complex set of questions.

My instict is till tha the total water requirement should be broadly 
proportional to the cross sectional area of the stem, and that guidelines 
could be developed from that.

Here's the bit where most arbs switch off, the arithmetic. But it's simple. 
Cross sectional area is pi x radus squared. But we don't know the radius, , 
just the diameter or the girth. Blah blah blah, but when you do the maths it 
comes dow to this, wtaer requirement is proportional to teh squesre of the 
girt. All that's needed is a figure in litres (per week).

So, for example, say a tree with girth 20cm. Square that equals 400. Multiply 
that with the magic number, which seems to be about 0.2 (litres per week).

To repeat to show how easy it would be. Girth (in centimetres) x girth x 0.2 
is the weekly watering requirement in litres.

If that's too precise, a table such as Ben's could be drawn up for various 

As ever calculations are available on request. I'm doing that instead of 
putting them in this email because that's the only way I can tell if anyone 
cares to understand.

Julian A. Morris - Professional Tree Services  and
0778 XXX XXXX - 0141 XXX XXXX

Sent: Tuesday, February 11, 2020 at 10:15 AM
From: "Jon Heuch" <>
To: "UK Tree Care" <>
Subject: RE: Watering trees during the establishment phase

I am afraid that attempting to define how much water a tree needs in writing
is prone to problems when the text is to cover all eventualities, including
idiots who may read the instructions and apply them to the letter.

This story does have some relevance, so persevere:

I remember a tale told of me in a live forest fire situation; the fire
needed to be put out ASAP, so the radio  message went out "Send the bowser
to location X ASAP, emergency". The two staff members got into the bowser
and drove it like crazy to the fire. Great! Problem solved. Now put the fire
out! The hose was extended, the pump turned on, and a drizzle of water came
out of the hose for a few minutes. No water in the bowser! No one had told
them to fill the bowser with water. However, the instructions were followed!

So, in a fire season, resources are deployed according the severity of
conditions. Typically a fire index is calculated based on temperature, wind,
relative humidity and previous rainfall. A high index means every body is on
high alert; a low index means that everyone can stay in bed.

Watering trees has a similar feel. It's raining and has been raining for the
last week. You probably don't need to spend much time watering your newly
planted trees. If it's been 30 degrees C every day for the last week, and
the last time it rained was a month ago, you are probably going to spend
more time watering. You can make it simple - just water during summer months
& you may get waste & complacency (operators can cheat, get paid for doing
nothing); or you could be a bit more sophisticated and base your watering
regime on recent weather. MORECS might do the trick but the data costs.


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The UKTC is supported by Bosky Trees arboricultural consultancy