To be dreaming about a harvest indicates that we will reap the rewards of previous care we have taken. We are able to work hard, and in working hard we take care of the future.
So, to dream of a harvest can actually have two meanings.
It can mean looking back into the past and reaping the rewards, or it can mean looking towards the future in order to use what has happened previously.
In previous times, for many the hayfield represented fun, relaxation and irresponsibility. Nowadays it is more likely to represent irritation – as in hay fever – and an unknown quality.