I have a little plastic greenhouse. I usually plant seeds (veg/flowers), in April or May time. What can I plant in seed trays/greenhouse during Sept/Oct. Would that be onions? Sorry, bit thick, but have gladly jumped onto this sharp learning curve.
There are lots of quick growing veg that can be sown now for a catch crop, and specific "over winter" veg as well... there has been a couple of threads recently and a more technologically proficient person will probably paste in the link for you.... ;D
you can start your japanese over wintering onions and salad crops.
In final planting position you can pop some carrots and spring cabbage in.
Have a look at http://www.rhs.org.uk/vegetables/seasons/autumn.asp
And these:
http://www.allotments4all.co.uk/smf/index.php/topic,44450.0.html
http://www.realseeds.co.uk/summersowing2.html
That lot should keep you busy for a while.
;D