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.”
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.”
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.
“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.