Posted: 23/10/2013 at 14:23
When you said "Is there an ideal base for a conservatory?" I take it you still meant "greenhouse".
(The modern meaning of conservatory - a "living room" room built out into the garden would definitely imply the need for proper concrete base and footings for a low level wall.)
I'll assume you were still referring to installing your 2nd greenhouse.
II assembled my own lightweight 8' x 6' greenhouse (green aluminium frame with polycarbonate sheet windows) directly onto well levelled, well compacted soil which I covered with good quality black membrane and shingle on top of that. A narrow central path of slabs running from the door to the back makes it comfortable to stand on.
Of the other two options,
- I would not want a full concrete base (no drainage for your plant watering)
- Bare earth is fine if you actually want to plant I to the ground - I would still want a central aisle to stand on though as quite a lot of watering could be needed inside for your planting as it will get none from outside and what it does get will soak into all the soil, some of which you will have to stand on.
- The advantage of my arrangement (photos) is that pots can stand on the shingle which drains easily after watering. The disadvantage is the membrane and shingle stops you from planting directly into the ground.
Virtually no weeds have made there way through the membrane in the 15 years it's been up - just a bit of chickweed which is easy to pull up.
The only bits of concrete were a large block at each corner and (if I remember correctly) half way along each of the long sides, to imbed the corner anchorages for the frame while the concrete was wet.
Positioning for these anchorages, however, has to be exactly measured and the frame (seen as grey in this photo) must be completely square and completely level for the greenhouse to fit together properly. I know that sounds worrying but it just takes a bit of careful measuring and checking for levels.
Hope the above helps.