Page 55 - ALG Issue 2 2015

Pots of Invention
Plant pots are plant pots, aren’t they? I mean they are either plastic or clay. Well, apparently success or failure may depend
on your knowledge of the humble plant pot. So many variations
of it have come and gone over the years such as the ‘Tell Tale Pot’, given its name because its colour turned darker when
damp. Then in 1830 the Bygrave Plant Preserver appeared, a terracotta circular contraption, with larger models made of lead
to deter slugs. In 1876 the Germans started manufacturing pots from compressed cow dung mixed with soil. Other materials included leather, glass, paper and zinc. The aerating flower pot containing air tubes appeared in 1884. A gentleman named Mr Tebb designed a travelling plant pot, constructed of paper lined with a waterproof material and had scalloped fold-over tops which appeared in The Gardeners Magazine in 1880.
However, clay pots reigned supreme with their flat bottoms
and poor drainage and which nurtured the myth of crocking, supposedly to improve drainage. Weird and wonderful crocking recipes abounded in the early years, including placing layers of coarse peat, half rotted leaves and, in the bottom of very large pots, inverted turves. Science has now proven that no matter what you put in the bottom of a pot, it will not improve drainage; in fact it can make it worse. The problem was overcome in the 1950s with the introduction of the plastic pot. A quick look at even the cheap thin plastic ones will reveal small protrusions on the bottom that leave the drain holes clear of the ground so that any excess water can drain freely; problem solved.
Even so some of the diehards were not convinced. So the ‘Glasshouse Research Department of the National Institute of Agricultural Engineering’ got involved and carried out their own investigations. They discovered in trials “that the plastic pot did not dry out so quickly and that it drained much more efficiently. Plants
in plastic pots used only a third of the water of those grown in clay pots in the initial stages, the proportion rising to one-half in the later stages when the plants become larger. The ideal plastic pot for tomatoes was summed up as requiring the following qualities: rigid but not brittle, easily cleaned and packed, containing a large volume of soil per plant, transparent, chemically inert and efficiently drained”.
“The plastic flowerpot provides the amateur with a greater margin of safety than the clay pot”, reported the “The Gardeners Chronicle” on the 5th November 1960, “especially if he is absent from home for long periods and cannot apply water to his plants just when it is needed”. In the book ‘Cactus Culture Based on Biology’ by Dr Buxbaum, he
suggests “that the constant evaporation through the sides of a porous pot leads to a concentration of salts in the wall and the leaching of the soil in the centre so that the
roots are attracted to the wall where the fifine root hairs, by which alone the plant can
absorb water, may easily be
pot stands in the hot sun and becomes dry”.
Even with all the trials etc. there is still one major thing wrong
with today’s plastic pots, in my opinion. This is something that manufacturers need to address...they are the wrong colour. White plant pots, as opposed to black or terracotta, encourage stronger plants because light is reflected off the inside of the pot onto the seedling, resulting in much better growth. It is for this reason
that initially, I always use the white plastic vending cups for all my seedlings, it also does away with plastic labels as you can write the name on the pot. Try it and see the real difference, but remember to make the holes on the side of the cup or you will have the same problem as the old gardeners did with the clay pots.
Rob Foster www.thelazygardener.org
damaged if the
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