I have read a lot about using coffee in the garden, it’s in the news all the time, but what about the nation’s favourite drink...the good old cup of tea?

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We all take a large proportion of what is told to us as gospel -  truths such as chameleons change colour to blend in with their surroundings, or that we lose most of our body heat through the top of our heads or that goldfish have short memories or that owls have eyeballs. We believe things that we have always known, don’t we?

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So, as I was pouring tea onto my blueberries the other day in the sure knowledge that I was doing some good, it occurred to me that I could be fooling myself. This thing I had always ‘known’  could just be another gardening myth.

 

The theory

When I was at college one of my professors used to routinely poor the dregs of his tea (no milk, no sugar) onto the African violet on his desk with a cheerful ‘there you go sonny, have a cup of tea.’ He was well-known for it, but luckily he was well liked so we forgave him his eccentricities, and besides as budding horticulturists we all knew that tea was acid and African violets like acid soil.

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Never a fan of African violets I had never done this myself, but  this little bit of knowledge was stored away in the back of my mind and when I started cultivating blueberries I also started saving the remains of my tea and pouring it onto these acid loving plants. Living, as I have done for many years, on the limestone escarpment of the Cotswold hills, my garden soil is anything but acid, so I have always grown my blueberry plants in raised beds, planted in a mix of pine bark, horse manure, leaf mold and soil from my garden. Around the base of all the blueberries I have planted strawberries (which also grow well in mildly acid soil) and they also shade the roots which means that I don’t have to water as often as I would otherwise have to. Although this mix is naturally acid, because the bed is raised and I water these plants with a combination of grey water, run-off from my greenhouse roof and  some tap water the effect over the years is a slow sweetening of the soil through the use of the local, limey water and the effect of leaching. Hence my nonchalant reliance on tea to correct the balance. But was I doing any good at all?

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The test

In order to test this out I filled 2 x 5 litre pots with left-over soil mix from the blueberry bed and tested the soil using a simple pH test kit from my local hardware store.   For four weeks I watered the two pots with water from the hose, but one pot also had a weekly dose of left-over tea. At the end of the 4 weeks I tested the soil again to find out if the pH had,  indeed, been altered.

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The truth

It had been altered a lot.

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At the beginning of the four weeks both pots registered  a pH of 7.   At the end of the four weeks the tea-less pot registered 7.5 on the scale, slightly more alkaline than when I had begun, whereas the pot that had been given the cold tea registered a massively reduced pH of  6, well into the acid range. No wonder my blueberries are happy.

The tealess pot had been subject to the constant watering with alkaline water which must have resulted in the increased alkalinity while the tea pot had obviously been subject to the acidification of the tea which was more than a match for leaching through of the lime-laden Cotswold water.

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I have occasionally read claims for cold tea to be used as a source of nutrients, but I haven’t any experience of seeing it used for that purpose, nor have I read of any studies that support this idea. However ericaceous plants thrive in the low pH environment that is created by pouring cold tea onto the compost so it will appear as if tea is rich in health-giving nutrients.

The use of tea as an acidifier will only be efficacious if the plants are in the controlled environment of pots or raised beds. Trying to influence the pH of bed or border soil with the occasion cup of tea would be asking a bit too much!

While by no means a comprehensive trial, this, together with the undeniable proof in the form of a reasonable blueberry harvest each year  proves that regular applications of cold tea will alter the pH in raised beds or pots.

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House plants that may appreciate the acidifying effects of left-over tea

Azaleas

Begonias

Amaryllis

And of course, African violets!

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Garden container-grown plants that wont say ‘no’ to a regular cup of cold tea

Strawberries and blueberries

Blue hydrangeas

Pieris,

Winter heathers and heaths

Camellias

Kalmia

Skimmias

Raspberries (yes, raspberries can grow in pots!)

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Oh, and, by the way,in case you didn’t know, all those ‘truths’ at the beginning of the article are, in fact quite false.