The Power of the Humble Tea Bag...

  • Article by: Dr Ken Thompson
  • Wednesday 4th May 2016

Ken Thompson is a plant biologist with a keen interest in the science of gardening. He writes a frequent gardening column in the Daily Telegraph, lectures extensively and has written four gardening books, including Compost and No Nettles Required. His most recent book is Where do Camels Belong? The Story and Science of Invasive Species.

A tea bag doesn’t look like much, does it? And a used tea bag, tossed casually in the bin, hardly seems worth a moment’s thought. Yet in Britain we drink 165 million cups of tea every day, and 96% of those are made with a bag, so that’s a little over 158 million tea bags per day. Even if you can’t picture a great steaming heap of 158 million used tea bags (no, neither can I), that clearly is worth a thought.

In fact, several thoughts. The first is that over 57 billion tea bags per year is quite a lot of landfill. Most of us have gardens, and if you have a garden but don’t have a compost heap, in my opinion you have some explaining to do. If you do have a compost heap, as you should, then that is your tea bag’s natural destination. Tea bags are just another variety of green waste, along with garden waste, kitchen vegetable waste, and almost anything else that used to be alive, including coffee grounds, hair, egg boxes, cereal packets, vacuum-cleaner dust (mainly dust mites and flakes of human skin, and therefore highly nutritious), nail clippings, rabbit or hamster bedding, general floor sweepings and old cotton or wool clothing.

Tea bags are, after all, just leaves. Mostly tea, of course, Camellia sinensis. Tea leaves will break down in your compost heap, just like all the other leaves (e.g. lawn clippings, weeds etc.) that normally go in there. In fact, ecologists who are interested in how the environment affects decomposition have proposed using tea bags as a standard reference that can be bought and used anywhere in the world. However, they want a tea bag that will stay in one piece when buried, so they can measure decomposition of its contents. There is such a tea bag, in which the bag is plastic, but that’s very unusual; not only that, it’s emphatically not what you want in your compost heap.

Fortunately, in the overwhelming majority of British tea bags, the bag itself is made, rather surprisingly, from bananas. Not the ubiquitous yellow fruit, but the closely related Musa textilis: abacá or Manila hemp. The fibre from the leaf stalks of abacá is both strong and fine, in fact just what you want for tea bags and other specialized paper products such as filter paper and banknotes. But despite its strength, once in your compost heap the bag will break down just like any other vegetable matter.

Teabags in a kitchen compost binYou will occasionally read that tea bags are not entirely biodegradable, which is true - up to a point. So that the bag will seal properly, it contains a very small quantity of the plastic polypropylene, which melts when heated and so can be used to make a secure seal. But although polypropylene does not break down in the compost heap, it does break up, so it’s hard to find any trace of a tea bag after six months in a compost heap. Moreover the quantity involved is minute, scarcely a drop in the ocean compared to other plastic waste, such as carrier bags, bottles and plastic packaging.

But never mind what you can do for tea bags, what can tea bags do for you? Few gardeners can make enough of their own compost, so it pays not to ignore any source of organic matter. There may be only just over 3 g of tea in a single tea bag, but that’s still over 180,000 kg of useful organic matter every year (dry weight - obviously a lot more in the soggy state). Nor should we ignore the bag itself, which is about 1/10 of the weight of the tea.

In addition, although it’s the bulky organic content of compost that improves soil structure, retains moisture and suppresses weeds, there are useful plant nutrients in there too, and here again tea bags can make a contribution. As leaves go, tea is actually towards the high end of nutrient concentrations, with about 4 % nitrogen and about 0.5 % phosphorus, so Britain’s annual consumption of tea bags represents over 7,000 kg of nitrogen and nearly 1,000 kg of phosphorus. All things considered, one thing’s for sure - used tea bags are far too valuable to just throw away.

Image credits:
Tea bags - André Karwath taken from Wikipedia
Tea bags in compost bin - The Guardian website, photograph by Simon Hadley/Alamy

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