I used to be a lecturer at Edge Hill but they've slowly been decimating the courses (mainly Arts/Humanities in favour of STEM) so I lost my job along with dozens of others.
I don't know anything about the Plant Sciences course (to be honest I didn't know they had one!) but, with your sons predicted grades, I think Edge Hill might be a good option.
The campus is stunning and the accomodation fantastic. You get the uni experience but in a very safe environment. I loved London as a teenager and couldn't wait to get down there for years on end so by the time I moved there to study I was overjoyed and very excited. I was very surprised to absolutely hate it, feel unsafe, struggle to make friends (people seemed so cold and distant compared to my hometown) and find it very expensive - it is financially crippling to study in London unless you have family already living there. I know I would have been much happier at Edge Hill. We didn't have many problems with homesickness, compared to other universities I worked at. The students are a really nice bunch, it's not at all "edgy" or "rough". It is rural, in a small pretty country town called Ormskirk.
That being said, if he wants a bit of city life then Liverpool is 20 mins by train and Manchester not too far either. There are also cities and towns like Preston, St Helens, Warrington, Chorley, Wigan that aren't too far so it's not cut off at all.
The management is very keen on the "student experience" being at the forefront. There are lots of initiatives to keep students happy...there seemed to be a major event most weeks. Christmas Fair, Therapy Dogs, "Feelgood February" etc. There are excellent gym, sports, swimming facilities, the library is fantastic, there's a theatre which (as well as student shows) has visits from well known comedians, free cinema etc. Students can study a language for free too and the student societies are excellent and varied. Dining is fab. Gahhhh I really miss working there!
There are videos on Youtube by students on living at Edge Hill, check them out and visit too.
Do ask though about recruitment...if there's 10 students or less each year it's likely the course will be phased out.