He intends to sell their products directly to customers by mail order, internet, telephone and on television after TV shopping company Ideal Shopping Direct (ISD) completed its buyout of the business last week.
"We would encourage any grower or supplier with new products or stock they want to liquidate to contact us. We'd be delighted to talk to anyone we're not talking to already," said McDermott.
"We have a number of routes to market. TV shopping is a voracious consumer of product. This is an opportunity to make the industry better and we'd like to be a part of that."
ISD bought LTGL for an initial £5m, of which £750,000 will be in cash and the rest in the issue of initial consideration shares. A further £2.2m may be payable in earn-out consideration shares, subject to the achievement of a pre-tax profit target by LTGL of at least £800,000 and up to £1.8m for the year to 30 June 2010.
LTGL turned over £5.8m in its first 17 months of trading to 30 June 2009, with profits of £730,000. McDermott said he hoped turnover would be in the "tens of millions" in the next three years thanks to the backing of ISD, which has a turnover approaching £100m a year.
McDermott said LTGL, which uses the Garden Bargains brand, sold everything from seeds, bulbs, plugs and liners to 10-litre trees, as well as a wide range of gardening hard goods.
He explained that the grow-your-own and stay-at-home trends had helped to build the business since 2008, along with "a phenomenally large amount of hard work from the entire team".
McDermott said there was enough space for competitors "to all do their own thing" and move on from copycat advertising that "has been a major frustration for years".
He pointed out that Crocus, Greenfingers, Suttons, Unwins and Thompson & Morgan were in similar markets but had their own databases.
He also said video marketing on LTGL's website would continue to be important "because of the knowledge gap at the consumer end of the market".