Steer, who works at Madingley Hall University Institute of Continuing Education, explained: "Horticulture is getting more attractive. Opportunities in the industry are huge and meet most people's interests from science to garden design and plant history, botany and ethnobotany. You can branch out into whatever you want.
"The big obstacle to people coming into horticulture is salaries. The skills required are not always commensurate with working in other industries. Using the same range of skills and qualifications elsewhere, you would be paid more.
"But some sectors of the industry are very well paid with extra benefits recognising and valuing the skills people have in horticulture."
Steer, who was third last year, beat RHS Wisley student Mia Laucht after the competition went down to the last three questions.
Third was Warwickshire College Pershore's Douglas Mackey. RBG Edinburgh's Frances Keeton, Reaseheath College's Kathryn Owen, Askham Bryan worker Aaron Hickman, Glasnevin's Michael Beckett and Bicton College's Rowanna Shorney also reached the final, hosted by Kew.
Among the guests were Lord and Lady Taylor of Holbeach and Kew director Professor Stephen Hopper. Sponsors included Shropshire Horticultural Society/Percy Thrower Trust, MorePeople, the Horticulture Development Company and Bulldog Tools.
Kew student Alex Summers won in 2009, netting a £2,000 Percy Thrower bursary study trip to Borneo. The 19-year-old competition is open to under-30s and attracted 1,500 entrants.
Steer beat last year's runner up James Hearsum in her heat. Competitors answered questions about horticulture in buzzer and individual rounds and had to identify plants and tools.