What’s in your compost?

By Richard Wright

Published on Tuesday, July 12, 2016 - 10:30


What’s in your compost?

Leaf curl on Edward and Brenda Bunkham’s tomato plants.

GARDENING THE Royal Horticultural Society has confirmed weed killer has been found in compost, following IW reports of unexplained tomato leaf curl.

It appears to be an unexpected side effect of the government’s encouragement for compost companies to cut down on the use of peat.

The effect has been for them to look to other bulking agents and that has led to many of the proprietary brands incorporating substantial quantities of composted green material from council tips.

That would at first blush appear to be a great thing because it reduces by a vast tonnage the amount of waste going to landfill but it has been pointed out that, unlike some countries in Europe, there is no control of the content — literally anything can go into the composting bins.

I have received more reports of tomato leaf curl this year than any other and while the causes can be many, from infection to cold snaps stressing plants, Ted and Brenda Bunkham, of Sandown, have uncovered contamination by a persistent weedkiller, which lingers in bags of compost that every customer expects to be clean and wholesome.

Ted and Brenda never use weedkiller and have gardened for more than 50 years, so they were both alarmed and upset when their tomato plants developed all the signs of poisoning.

They were forced to change all their compost, wash down the greenhouse and write to the compost company, which in common with others, has confirmed it is actively looking at ways of replacing the current green waste content.

In a frank letter to the Bunkhams, a company representative confirmed, without offering a refund: "Unfortunately, it is the composted green waste that more often than not introduces contaminants into the compost mix.

"Kerbside collections from millions of households are common and are obviously open to being used for debris of all kinds by the original householder or by passers-by while the bin is awaiting collection.

"Due to this problem, we are currently looking into alternative sources of non-peat materials.

"In contrast, other countries of Europe, such as France and Belgium, only use green waste accepted at manned receiving stations where visual and physical controls ensure a much cleaner raw material with very little contaminants.

"Unfortunately, green composters in the UK do not receive such clean material and are currently working closely with local authorities, collection companies and the public to try to reduce contamination."

The RHS confirmed to Brenda and Ted it too is examining the scale of the problem and if it finds it to be widespread will be seeking regulatory help.

RHS principal horticultural adviser Leigh Hunt said: "Your tomato plants are exhibiting symptoms we associate with weedkiller damage, rather than aphids, stress or plant viruses.

"As the plants in question were growing in growbags or pots, it is very likely contaminated growing media (compost) is involved.

"RHS members have reported more weedkiller damage type questions than usual so far this year.

"We suspect the current cases involve composted landscape and garden green waste (a component of some peat-free potting composts and growbags) inadvertently contaminated with grass clippings treated with a persistent lawn weedkiller called clopyralid."

• The Which? top performing compost of the year was recommended by the RHS because it does not contain green waste. Sadly, SylvaGrow is not available on the Island.

Reporter: richardw@iwcpmail.co.uk

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