Garden industry bodies are seeking robust and economical gardening sales data, with a number of projects coming under discussion this month.
The HTA hopes to launch a seeds and young plants data-collection scheme on behalf of members this season.
Suttons Seeds sales and marketing director David Arnold said a previous scheme run by the UK Agricultural Supply Trade Association came to an end a decade ago.
A recent meeting with HTA's Martin Simmons involving 15 companies showed the need for such as scheme, which would help "understand the dynamics of the market", said Arnold.
He added that individual companies know how they perform but have to guess at what is selling. "We don't even know the size of the market, which is barmy".
Garden Industry Manufacturers Association (GIMA) council member Jane Lawler is also working on a market data scheme to help manufacturers and retailers monitor sales and trends and to help gauge the size of sectors more economically.
Lawler, marketing director at Gardman, said market data firm GfK had "coded" the wild bird care category but she was reluctant to pay it a five-figure sum for market information.
"From a GIMA perspective we have had conversations about potential methods of collecting market data. I'd like to see something in place that is relevant and has everyone's respect."
Lawler said she was discussing collating reliable hard data for the wild bird care industry through a route outside the GIMA, where companies would submit data to a single point. "But there has to be a high level of trust," she added.
The Crop Protection Association operates a scheme for fertiliser and chemical retail sales. It shows that UK sales fell from £63m in 2011 to £53m in 2010. Companies such as Vision Critical, which supplies market research software, are moving the market from collecting electronic point-of-sale (EPOS) data from retailers to collecting sales data from suppliers.
Leisure & Outdoor Furniture Association secretary Phil Gibbs said the body was looking at it as an option.
Hozelock marketing director Simon McArdle added: "We use GfK and EPOS data that show we have 72 per cent of the market, so we're in an unusual position. But if I worked for a different company, I would see the value."
Sinclair retail managing director Danny Adamson said GfK estimates of the growing-media market at £150m a year were low because it does not cover all retailers. He said the market was £255m, while the HTA estimated £300m.
GfK admitted that it was struggling to pick up new clients in horticulture.
HTA marketing director Andrew Maxted said: "Access to robust market information is key to helping businesses of all sizes grow and prosper. We are looking to build on our Garden Retail Monitor to enable the sector to benefit from wider industry data."
Submitting Data - Pet food industry points the way
A system like the one used by the Pet Food Manufacturers Association, where all manufacturers give sales information anonymously, would be a boon for the horticulture industry, according to the association's chief executive Michael Bellingham.
"Members who wish to take part submit data on annual sales and average retailer margin. That data is pulled together by an independent person and we estimate the size of the market.
"The scheme has been going 10-15 years and around 30 companies take part."
He continued: "The fact that they choose to continue means that they find it useful. We use it to find out the state of the market, trends and to lobby.
We also provide headline data to the media.
"We offer it as a service to members. It's different from Euromonitor, which uses data from supermarkets and doesn't account for specialist retailers. We're the only one with a complete overview."