Wednesday 17 February 2016

Are gardeners too precise?

Do your sums in the garden but fussing about is a waste of your time!
It might even be detrimental

How on earth can I calculate the area of my lawn?
Many years ago  the UK ‘went metric’ - did it really happen? What acutely annoyed me was how newspapers and gardening magazines would give dual recommendations with imperial numbers translated with great accuracy to metric. For instance, the legendary four ounces per square yard might appear as 135.6 gram per square meter!
How silly! Did no one tell them that 4oz per square yard was a hugely rounded figure, itself an estimation arrived at in someone’s fevered imagination? Even a sensible ‘scientifically precise’ recommendation would normally be equally valid plus or minus, lets say, twenty percent!
When you consider the extreme variability of diverse gardening situations where measurement is needed, even differences of several hundreds of percentage points usually works!

Take fertilizer as an example where a rate of 4 oz per square yard used to be often recommended for growmore. I confess I might myself sometimes think in these terms and reasonably make a mental calculation to half the rate to 2 oz per square yard when estimating my stronger and superior Yaramila which has a somewhat different ‘balanced’ analysis.
But on what is my rate of fertiliser application actually based? Apart from the fact that it might be be a marginal decision whether to use any fertilizer at all? There are so many variables! The real need depends on the soil analysis, the physical nature of the soil, the nature and condition of the plant, the time of the year  - need I go on?  At best when I apply my fertilizer it is a ‘ballpark’ estimation. I vary my rates of application of fertilizer based on my so called ‘experience’. I hope I am right more than I am wrong. The good news is that when I am wrong, unless I have done something completely ‘off the wall’ it won’t really matter! If I apply too much nutrient most will still be there for my plants next year.

A blogger recently asked in a gardening forum how much sulphur he needed to reduce the pH of his soil from 5.7 to 4.8. He was seriously deluded that you can turn the pH on such a sharp pin! Tables of recommendations state figures for different soil types such as ‘sandy’. There are hundreds of subtly different sandy soils. The best answer to the blogger’s question admitted a ‘fudge factor’ of 100%. No one asked him why he required such an extremely low and precise pH. I disingenuously asked him what he was growing. The answer came back as ‘blueberries’. I had egg on my face in that about pH 5 is probably optimum for this crop.
You would be amazed at the methods used in the States to acidify soil!

I have a history with iron sulphate. When I wrote my post about it, it went down like a lead balloon! Now it is by far my highest statistic and had been read 50,762 times at 5.13pm on January 20th! How’s that for a failure to ‘round off?’

In that post I quoted an application rate of 10 gram per square meter for moss control in a lawn. This was my conversion from a quarter of an ounce per square yard, perhaps a ten percent ‘error’? I really felt quite brazen when my son’s photograph showed me flinging iron sulphate around. My inaccuracy in distribution is yet another consideration!

But where did that figure of a quarter an ounce come from? For my sins I once used to check copy for ‘Gardening Which’. I remember my glib satisfaction when I spotted the spelling error, ‘forget-me-knot’!  I also remember querying the rate of application for iron sulphate as between 1/4 and 1oz per square yard, thinking the latter figure a typo. I never found the truth about this 400% variation!
In actual fact when I apply iron sulphate - to control moss rather than just as a general improver - I deliberately  apply it unevenly. Where the moss is thick, perhaps where the lawn has been shaded by a flower border, I scatter more. This wet season some of the moss has even been sphagnum which is even more of a challenge. I suspect a few patches really do get 1oz per sq.yd. They need it!

I am confessing all today. When I find my lawn mossy I just go to my 25kg bag of iron sulphate and scoop some out into a suitable carrier and go out and chuck it at the mossy places. Retrospectively as I was writing this post I calculated how much I must have applied when I moss killed last month. It was just over a quarter an ounce per square yard average over the whole lawn area. But then I am a regular user, perhaps three times a year (notice the vagueness) and my moss is not all over.
This brings in another factor, one’s power of estimation!

Having a fling
Spraying weeds 
My most accurate work is with my knapsack sprayer. It is most important that I kill my weeds and not my plants. To this end providing an accurate uniform dose per area is of no concern whatsoever although this concept which is  legally and practically necessary for farmers, might provide a beginner with a rough guide.
My weeds are widely scattered, vary in density and nature and are selectively sprayed. My rates of chemical applied per unit  ground area are very much less than the amounts calculated for an overall application.

The concept most useful to gardeners is the strength of spray in their tank! My scientist friend Peter accurately makes up his spray tank for almost all of his spraying at a fairly strong 1 in 50 of commercial glyphosate to water. I (accurately and deliberately) vary my own  between 1 in 50 and a very weak 1 in a 100. 
My measuring bottle lives in my tank. The strength on the day depends on the weeds - stronger for nettles and epilobium, weaker if tiny weed seedlings are dominant. It might also vary a little with the weather (might it rain?), temperature and season. In practice it will usually be between 1in 60 and 1 in 70. My fifteen litre tankful of spray will cover as little as seven hundred square yards or as much as an acre. It depends on the weeds! For example if I meet a clump of  ‘difficult’ ragwort in Worsbrough cemetery my nozzle hovers over it for a split-second more.
It might amuse you that I use metric units to calculate my spray application and yet have strayed to square yards and acres in the above paragraph!

In my next post I have trouble with nozzles
This use of estimation and my apparently cavalier attitude to exactitude hide my ernest desire to do what is best for the garden. Recognition that ‘variables’ occur and that nature itself is not only very resilient but ‘plays the odds’ against environmental vagaries leads, me to speculate further about how excessive accuracy might not be the best way in the garden.

Take the depth of a seed drill. Obviously it will vary with the size of the seed and you might have some insight as to what is appropriate for your soil.Take it as evidence of my slovenly nature that my drills are never completely straight and I don’t use a string, board or line!
But other factors are at play. A deeper sowing might be best in dry weather. On the other hand if it is wet a shallower drill may be better aerated and if it is very wet certain seed might be better if not covered at all. At the time you are sowing you cannot read the future.  Am I just lazy or merely taking an each way bet when the uniformity of my drill does not pass muster?

Planting bulbs is another case where extreme variability in depth and usually failing to insert upright will often not matter. In my recent post I mentioned planting 1800 bulbs on Cathi’s new verge in a total time of about three hours. (Note that my posts are littered with qualifications such as ‘about’, ‘almost’, ‘often’, ‘sometimes’ and ‘maybe’. Brenda says I never make up my mind). When I plant bulbs I lever up a spadeful of soil, and without further disturbance tuck several bulbs under! Some might happen to be upright but most will be horizontal. They all grow and flower and thrive. By the time they flower their second time around all bulbs will be upright and nature will have decided the depth they prefer.

In actual fact nature herself plants bulbs very erratically indeed. A dense patch of snowdrops pushes surplus bulbs out of the ground. Not to mention rabbits that with the help of the wind, distribute them around where they root and grow. That’s how they spread naturally without any help from the gardener!

When we moved into Boundary Cottage I had a stupid prejudice against the Carlton daffodils dotted around the garden. I forked out the dormant bulbs and scattered them without planting in rough stubble on the roadside verge. They made a magnificent clump which continued for the next ten years. When the road was relaid and the edge was grassed down even though chopped and churned they just carried on

See what the rabbits did in Cathi’s garden - I have lost my best picture that showed hundreds which I scooped up to plant in her new verge.

But what about my provocative subtitle which suggests excessive accuracy can be a bad thing?
It was rather ‘tongue in cheek’ and usually the greatest damage of too much precision is spending precious time faffing around and neglecting a more urgent task in another part of the garden! 
If I were to ‘rake up’ some examples they might include amateurs messing around with next-to-useless soil analysis products bought at the garden centre. It is fifteen years since I needed to use a pH test and I have never had my soil analyzed. Perhaps I should? Regarding professional analysis done for you by a laboratory the real genius is to correctly interpret the information you receive.

Striving for uniformity raises my ire. When I weed kill my lawn I follow the weeds. When I spray my borders I refuse to spray at a constant pressure as is often recommended. It does not apply to the spot spraying I do. When I fling fertilizer I have no need for a distributer. Peter commented only last week how his spreader had clogged up yet again and he had once more needed to buy a new one. 

What is the point of applying water mechanically and uniformly in a greenhouse when all the plants need different amounts?
Fun in Funchal
We have just returned home from our holiday in Madeira with botanist Mike Ashford and his gardener wife Isobel. We met up at Funchal botanic garden with Peter Williams and Julie who were there on a walking holiday. Knowing I had just written this post I thought it too good an opportunity  to miss to test them on their powers of garden guess-timation.
When viewing from above I asked them to estimate the area of the garden's signature rectangular carpet bedding.

Funchal’s manicured carpet
Peter immediately said 900 square meters, he says he got there by mentally visualising his own lawn of known area. Mike was more  reticent and made no disclosure. On hearing Pete's suggestion I immediately halved my own to one third of an acre!
We agreed to go down and pace out the area.

Imagine the three old fogeys from ‘The Last of the Summer Wine' pacing this crowded place. Diminutive  Welsh Peter striding and determinedly pacing. Me and Mike diffident, pretending to be just walking. Mike nearly fell off the wall. I did not ask them if their strides were metric or imperial.
The width was easy. One could guess it was twenty metres and round off our strides. We all agreed twenty meters. The length was a smidgeon more demanding but we all came to seventy five meters giving an area of one thousand five hundred square meters.
If our effort proves anything it is that pacing is usually good enough for gardeners!

When I was at college our tutor asked us to debate whether horticulture was an art or a science. I still don’t know the answer.


  1. Canada went metric 40 years ago and I still use a mixture of metric and imperial. I use only metric for temperatures and long distances but visualize length in feet rather than meters. Some things did not change like the size of lumber (2"x4", 2"x6" etc.) in the construction industry. If we were not next to the US the change would be more complete. Clerks in stores no longer understand if you say you need 10 feet of something.

  2. No precision here only when weighing produce.

    1. And what fantastic produce you grow Sue. I wonder how your yield per unit area from your allotment compares with farmers and growers? Far higher?
      I have no idea of the weight of my home grown greens I eat in a single serving but it is much more than the adman's five a day!

  3. It is good to know I can be more relaxed about these things. I managed to buy some Yaramila complete fertiliser via a friend though an allotment society,£21 for a 25kg bag.

    1. Thats a very good price Brian - cheaper than East Riding Horticulture where I buy mine.
      I will be interested in due course to hear how you get on with it. Perhaps you could comment again on this post at the end of the season?

  4. As my old mum would say, stop being so bloody pernickety!!. Hope that's how you spell it erm, well, there I go again, sorry ma

    1. Clearly your mum was a very good gardener Alistair. And she called a spade a spade!

  5. A handful thrown over an area which looks about right is my way these days, a long way from working out tractor speeds etc!

    1. Me too Rick.
      The problem is helping new gardeners get a feel for how much is needed


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