Garden leave is legally considered to be a type of restraint of trade since it keeps employees out of the market. As such, it must be reasonable to be legally enforced.
The maximum period of garden leave must normally be no more than about six months.
If the notice period is longer than six months then check whether the contract allows you to start the garden leave part-way through notice, so the maximum is not exceeded.
The reasonableness of garden leave must be considered alongside any post-termination restrictions, so consider the overall period of restriction. If the total period is too long then you will have to choose between using garden leave and the post-termination restrictions.
If you must choose between using garden leave or relying on post-termination restrictions, remember garden leave is normally easier to enforce if there’s a dispute but is more expensive, as the employee is paid for not working.
If in doubt then Ask a lawyer about this tricky area.