Check the tempereatures in greenhouses during the day as well as during the night, not too cold but not too hot either.
Now is a good time to fix and replace any shed roof leaks, broken glasshouse panes, or worn glazing putty!
Does your greenhouse heater still work? Now is a good time to get electric or gas heaters serviced if necessary!
Tender plants should be brought into a heated greenhouse for the winter: have you already finished doing this?
Insulate your greenhouse: you could use plastic bubble wrap! However the wrap will reduce light levels somewhat!
Greenhouses should be damped down on hot days! Some tips for purchasing a new greenhouse: http://j.mp/Mh6JCg
Do you have a greenhouse? There are some good reasons to build one! Some considerations: http://j.mp/IPgZif