The Association of Professional Landscapers (APL) and the Arboricultural Association urged people last week to use accredited contractors to repair or remove storm-damaged fences, sheds, bushes and trees.
Last year, the Government watchdog Consumer Direct received more than 5,700 complaints about rogue traders for home and garden maintenance work, said APL committee member Stuart Marler
"Employing a landscaper to do repair work can be hit and miss, with homeowners facing a lottery of companies," said Marler, who works for TVG Landscaping.
Arboricultural Association director Nick Eden added: "Stormy weather is often the most likely time for cowboys to call. Because it's an emergency, consumers will often go for someone without insurance or accreditation."
Landscape consultant Mitch Westwood, a BALI adjudicator and expert on the BBC consumer affairs TV programme Watchdog, said: "The economic downturn is forcing some contractors to buy work to keep their guys busy and cut corners."
Expert witness work in courts, which used to account for five per cent of Westwood's turnover, is now 30 per cent. He said most cases were down to people cutting costs or time on site.
The warnings followed figures from Oxfordshire County Council's trading standards service that revealed bad garden and tree work had become the most common complaint, rising by nearly 50 per cent last year.