As far as SF&G is aware, there is no funding specifically available for setting up a care farm. Some care farms have accessed money from DEFRA for capital works and others have received money following bids they put in to charitable organisations.
Awards for All Lottery funding does allow for feasibility studies including business planning grants of up to £10,000, but the procedures are changing and community benefit must be demonstrated. This is not available for individuals though, only for charities or social enterprise groups.
National Parks have got Sustainable Development Funds, which may apply to care farm projects and some of this money is available for setting up pilots or fact finding visits.
If you are based in Wales, The Development bank of Wales might be able to help you.
ESF (European funding) is available in certain deprived areas to pay for revenue, running costs and capital expenditures. The various Community Foundations might offer help in finding grants.
There may also be funds available through ERDP (England Rural Development Programme), known as LEADER, which has both an agricultural and social slant. Use the website to find a local contact for your region.