Is compost actually killing my garden?

Contaminated compost may be the reason some gardeners are experiencing distorted growth in their vegetable gardens, the Environmental Protection Authority (EPA) says.

Three gardeners contacted Get Growing to say their tomatoes have become deformed – and they don’t know why.

The EPA says it is possible their plants have been damaged by compost contaminated with clopyralid and has issued an advisory notice to highlight the issue and prompt people selling and using these weedkillers to follow the rules.

These include restrictions on disposing of sprayed plants and lawn clippings. Some clopyralid products can only be sold to and used by workplaces.

“Some plants grown in compost contaminated with clopyralid can become stunted or distorted. Beans, peas, tomatoes, lettuces, carrots, and roses are most affected,” EPA general manager engagement Paula Knaap says.

Penny Allan, of Nelson, says her plants started growing well but when about 300/400mm high, the top leaves and flower stalks became deformed and stunted, with hard calluses.

“There is no sign of grubs, insects or discolouration on them,” Nelson says.

“The soil is neither waterlogged nor dry and I have the door and roof vent in my glasshouse open during daylight hours.

“It looked like the plants would not grow out of this state, so I have since pulled them out and disposed of them.”

She says she has been using bags of compost bought from gardening centres

and wondered if this was the cause. “I’d hate to think that this could be possible, but you can never be sure.”

Darryl O’Reilly-Nugent, of Kawerau, says he has the same issue.

“My tomatoes did the same thing. I have lost 23 excellent plants. Some of the early ones that I gave to friends survived.”

The EPA is encouraging people to

take more care to stop plants sprayed with weedkillers containing clopyralid from contaminating compost.

Clopyralid is used to control weeds in sports turf, lawns, and on farms. If plants sprayed with the substance get into compost, the compost can harm some garden plants.

EPA manager Paula Knaap says clopyralid breaks down slowly in sprayed plants. It will affect compost that contains weeds sprayed with clopyralid and even manure from animals that have eaten vegetation contaminated by clopyralid.

“It’s important for people to properly dispose of weeds or lawn clippings sprayed with clopyralid. Make sure they go to landfill, rather than in green waste collections or in compost.”

Sports turf, garden, or mowing professionals should put weeds or grass clippings sprayed with clopyralid in landfill – not compost, mulch or council green waste.

They should also tell their clients to send weeds or grass clippings treated with clopyralid to landfill.

Arable or pastoral farmers with crops or pasture sprayed with clopyralid need to ensure harvested vegetation or grazing animal waste doesn’t get into the domestic compost market.

The EPA advisory reminds people with livestock to keep animal waste out of compost if the animal has eaten plants sprayed with clopyralid.

Gardeners can make sure their compost doesn’t contain clopyralid if they buy compost certified as organic, ask their compost supplier if it’s been tested for clopyralid, or make their own compost and exclude weeds or lawn clippings sprayed with clopyralid.

“If everyone in the clopyralid supply chain follows the rules, we can ensure that compost is safe for gardeners to grow healthy plants,” Paula says.

The EPA regulates products containing clopyralid under the Hazardous Substances and New Organisms Act.

YATES The EPA encourages home owners to make their own compost and to send plants and grass sprayed with weedkiller to landfill.