Homebase trading director Matt Compton said the cards provide "big data" as part of the 19-million-member Nectar scheme. Average spend is £23 and for every £1 members spend on plants they spend £1.30 on other products, he added.
Member surveys show 47 per cent buy plants, 44 per cent lawn care and 18 per cent grow your own. This data means Homebase can tailor rewards such as "bounce back" vouchers to encourage return visits.
Compton said Homebase has profiled "Helen", a typical "home enhancer" customer who accounts for 61 per cent of sales and visits 4.9 times a year. Some 51 per cent of Homebase customers are over 50, six per cent buy plants online, 63 per cent are female, 92 per cent have a back garden and 58 per cent have a front garden.
"Emotional connector uses" were to grow your own (21 per cent), peace (42 per cent), wildlife (34 per cent) and entertaining (26 per cent), he added.
Mintel says the market will be £5.58bn by 2018, with a top range of £7.3bn and bottom of £3.86bn.
Compton said average customer spending was £131 in store, £202 on the web and £393 if shopping with both.
Garden Centre Association chairman Will Armitage said his two-year-old Armitage's loyalty card now has 30,000 members - half his customer base. Members spend £17.77 on average, compared with £9.84 for non-members.
Bents has a "Be Inspired" loyalty card, Gateacre has a "Seasons" card and Millbrook has a "Family" card.