The cross-government target aims to get one million people active through sport and another one million through wider physical activity, including gardening and active conservation.
The Department for Culture, Media & Sport (DCMS) is responsible for the sport figures, with the Department of Health (DoH) in charge of physical activity.
The DoH has not pledged any new funding for green spaces or gardening projects, despite paying lip service to the economic benefits in its Be Active, Be Healthy report. It estimates annual costs to the NHS of physical inactivity are between £1bn and £1.8bn.
The report states: "The opportunity to explore safe, attractive and interesting parks or streetscapes can be a significant motivator for recreational walking and cycling."
Green space expert Alan Barber said: "The Government has been paying lip service to greening and health for years but you won't get them to spend money on making green spaces better in order to promote healthier lifestyles."
The Government has put £140m into free swimming for children and older people as part of the targets. Parks consultant Sid Sullivan urged equal funding for green spaces.
"If the Government is serious about reducing obesity and improving health then parks are an obvious way to invest money," he said.
Organisations including the National Trust, Royal Parks and Natural England are involved in campaigns to improve health through open spaces. The Royal Parks works with Westminster Primary Care Trust (PCT) on an exercise referral programme and the National Trust has a partnership with Bassetlaw PCT to provide health walks.
An RHS representative told HW that funding to help with community gardening projects would be welcomed: "The RHS recognises the value of gardening for general well-being irrespective of age or ability. It would stress the need for joined-up thinking from the Government to implement this strategy."
HTA director of business development Tim Briercliffe said local authorities and firms might need to lead the way: "The Government is unlikely to put a large amount of money into gardening but local authorities could pull together consortiums, bringing garden centres into campaigns. It is about making the change at ground level."
The targets, which have only included gardening and active conservation from this year, were criticised by Liberal Democrat shadow Olympic minister Tom Brake in Parliament last week. He said including gardening as part of the targets was a way of the Government fudging the figures to meet its Olympic sporting legacy plans.
Barber said: "The DCMS has probably just learned that after the Olympics in Sydney, participation in sport in Australia went down. Claiming gardening as an activity, knowing that it is buoyant and they don't have to spend any money on it, solves all problems.
"How can they ... still act as if public parks, as cultural and sports provision, don't exist?"