Muliple sowings of Phacelia green manure

Most people plant crops as a each bit of ground gets cleared, rather than a green manure.

Phacelia is a good green manure, cut it and use the tops as compost and let it regrow -  but I would have thought crops were a better idea 

I know the feeling mr brambles.

I would suggest that you put down some form of green manure as you go which you can dig in later in the season to improve the soil. If you have brambles and couch it would suggest that you have unloved soil like I did when I moved into my plot. I didn't have the same weed problem but the soil was unproductive. So half of my allotment went down to buckwheat which stifled the annual weeds and was excellent for digging in during the first season to improve the soil.

This gave me time to get all sorts of things going on the other half of the allotment and to get things like compost heaps going.

The alternative is to plant a mix with ryegrass and clover to grow through the Summer and dig in the Autumn.