It is offering prizes worth more than £10,000, including the £2,000 Percy Thrower Travel Bursary sponsored by the Shropshire Horticultural Society.
The competition is open to any horticulturist who is below the age of 30 on 31 July 2011 and will operate through a series of open heats before regional finals and then a grand final.
Last year's competition winner Faye Steer said the contest boosted her confidence and enabled her to plan a trip to the Yunnan province of China using money from the travel bursary.
Entries for open heats close on 28 February. To find out how to enter, interested applicants should call the IoH administration team on 01992 707025 or email email@example.com.