Secret in the soil

David Walpole is a gardener who likes to know what’s going on in the soil and has made a particular study of the trace elements selenium and boron.

“I was having trouble with my vege garden and my sister who was visiting from Western Australia and had read about the work of Dr Rex Newnham recommended boron,” David says. “So I scattered around a teaspoon for every 10 square metres and everything came away. Not every plant needs it but the brassicas do, rhubarb, silverbeet and beetroot.” It is also beneficial for strawberries, apples, pears and avocados.

“Beans don’t like it though,” says David, “and boron is also a weedkiller so it has a range of properties.”


David Walpole covers his seedlings to protect them from neighbourhood cats. Photo: Sandra Simpson

Boron is one of the most common soil deficiencies worldwide, says David who was an industrial chemist for 10 years before becoming a sheep and beef farmer on the outskirts of Tauranga for 40 years. It is available as borax, a compound of boron, and in commercial mixes of trace elements.

Selenium, a mineral largely missing in New Zealand soils, has interested David for the past 12 years, his study including a trip to Finland where by law farmers must add selenium to fertilisers.

“A study in the United States found that those in a control group given selenium had half the rate of lung, bowel and prostate cancer of the general population – but there had been no change in the cancer rates in Finland.

“I contacted the professor who had done the US study, Dr Gerhard Schrauzer, and he said the difference was the dose – the study had used 1.7 micromolar of selenium per litre of blood but in Finland the level was about 1.4. New Zealanders have a level of about 1.0.”


Since adding boron and selenium to the soil in his Tauranga garden, David Walpole has had increased crop yields. Pictured here are broccoli (front) and curly-leafed kale. Photo: Sandra Simpson

David, who runs the Tauranga U3A health group, says  selenium added to the soil will also result in an increased crop yield.

He and wife Erica retired to the Tauranga home of her late parents, Jay and Eric Naumann, in 2005. Eric was a long-time principal at Pillan’s Point School. When the Walpoles arrived there were a couple of old citrus trees in the front lawn, and David has added more for year-round fruit.


Tangelos are just one of the many types the provide David and Erica Walpole with year-round citrus. Photo: Sandra Simpson

“We start with the Harwood Late orange in April and May, then mandarins in June and July, the Clementine and Satsuma varieties, navel oranges in August and September, prolific tangelos from October to December and Encore mandarins from December to March.

“I wasn’t getting many flowers on the Encore until a mate told me a bird should be able to fly through it so I thinned the branches and now it’s covered in fruit.”

This article was originally published in the Bay of Plenty Times and appears here with permission. 

Read an interview with Dr Gerhard Schrauzer.

Read a paper by Dr Rex Newnham on the links between boron and arthritis.


One thought on “Secret in the soil

  1. I dip the tip of a finger into Borax, the same with Magnesium Sulphate aka Epsom Salt and wash it down with some water, daily. Seems to do me very well over the years. Well let’s say since my trip to Antarctica 🙂
    ps lost all my memorabilia in a fire, caused by an exploding laptop battery, but for some reason your name David just popped up in my mind, made a search and I am sure I remember the person in the picture above, fighting cats. 🙂

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