Industry giants Focus, Wyevale and Dobbies are among almost 100 entrants competing with dozens of smaller players for the 17 titles on offer.
Winners trying to regain their crowns from 2007 include Garden & Leisure, Scotsdale, Petersham Nurseries, Thompson & Morgan and Palmers.
HTA vice-president and Scotsdale managing director Caroline Own said: "The Garden Retail Awards have a hugely valuable role in helping to continually raise the standards in our industry so we can compete effectively with ever-growing competition."
The awards ceremony will be held on 12 November at Kensington Garden Hotel in London.
Judges Steve Bradley, Val Bradley, Graham Clarke, Roger Crookes, Chris Day, Leslie Kossoff, Marc Rosenberg, Neville Stein, Doug Stewart and Eve Tigwell will decide the winners on 27 August.
The sponsors are HTA, Westland, Quinton Edwards, Hammond Philips, Greenfield Software and MorePeople.