The publiction for amateur gardeners claims that the nutrients in compost can degrade over time and wants manufacturers to print a production date on the packaging. Compost does not normally have a sell-by or use-by date on it.
The Growing Media Association (GMA) said: "GMA members believe they manage stock well. If consumers are dissatisfied with the quality of their compost, they should take it up with the retailer."
Westland technical development head David Coop said: "Ideally, we would advise gardeners to use compost within the season of purchase. However, we are confident that Westland compost would be stable and consistent the following year if stored correctly in a cool, dry place, away from direct sunshine. This is because we use ingredients such as peat and our patented West+ wood fibre in our composts, which are stable, consistent and reliable products, which don't break down quickly."
A Sinclair representative said: "Sinclair Horticulture's retail composts are formulated to have a long shelf life. Any deterioration is gradual and the product remains efficacious for at least two years as long as it is stored well (i.e. fully wrapped).
"We encourage garden centres to rotate their stock, but we have no control over this. Should the consumer buy discounted older compost, we would advise them to keep an eye on their plants and be prepared to start their fertiliser regime slightly earlier if their plants show any signs of nutrient deficiency."