Tooth has made 20 staff redundant after his £1.2m-turnover company, Trevor Tooth Garden Practice, went into liquidation last week.
The BBC Kent gardening presenter's business owes hundreds of thousands of pounds. The final straw came after the client who was to buy his Lloyds TSB Corporate Markets-sponsored Chelsea show garden pulled out because of financial problems.
Tooth said: "If you're trying to light up the world there is exposure and risk there. We've expanded over the past three years, which has been painful and left us exposed.
"I was left no option (but to go into liquidation). The Inland Revenue moved in on us."
He added: "I've put £180,000 into the business in the past few years. We had a £400,000 contract dropped because of the credit crunch. I've presented £300,000 of work in the past three months but none has been accepted. Medium-sized clients looking for gardens for £50,000 and below are holding onto their bonuses and not spending on garden design."
Tooth's design business, Canterbury-based Trevor Tooth Garden Design, is still operating.
He said: "I'm carrying on work as a garden designer. I've got to earn a living and try to pay the mortgage."
Tooth said he owes money to companies including Wyevale East, Palmstead and Howard Nurseries, adding: "I apologise to those who haven't been paid."
Some plant suppliers have told HW they are finding it harder to collect money from contractor customers. One said: "We're seeing the first signs of things stretching out" - adding that housebuilders hit by the credit crunch were not paying their contractors, who in turn were taking longer to pay sub-contractors and suppliers.
On the garden design market, show-garden builder Mark Gregory said: "The bottom of the market is suffering but we're above the cloud line, although a lot of big projects have been put on hold.
"Short-term pain is long-term gain for the industry."
TV gardener and designer James Alexander Sinclair said: "When there is a credit crunch the luxuries like a new garden go first."
TV gardener and designer David Domoney said: "Show-garden building is a very dangerous game. You have to build your contingencies in. Sponsorship has been significantly harder to find this year."
RHS head of shows Stephen Bennett agreed show-garden sponsorship from some businesses may be more difficult to find: "We are fully expecting, because of the downturn in the building and associated trades, they will be feeling the pinch."