A greenhouse is only as good as what it stands on. An aluminium frame on uneven ground twists, the doors stop running, glass panes pop out and a strong gust can lift the whole thing. Plan the base before you order the greenhouse.
Steel base, plinth or nothing?
Check what comes in the box first:
- Palram Canopia includes a base plinth with its greenhouses. It still needs level, firm ground underneath.
- Halls and Vitavia sell the base as an extra on most models. Check the product page, as shops sometimes run offers on bases.
- Elite builds a base plinth into the frame of the Belmont, but it still needs a flat, hard surface.
A steel base gives the frame a square, rigid footing and lifts it off the wet ground. It does not replace a level surface.
The base types
Paving slabs
The most common base in UK gardens. Lay slabs on a bed of sand and cement over compacted hardcore, then check with a spirit level in both directions. You can lay slabs under the whole greenhouse, or only a ring under the frame and leave soil borders inside for planting.
Concrete
A concrete slab is the sturdiest option for large and heavy greenhouses, such as big glass models with toughened panes. It takes more work and is hard to move later.
Timber base
A frame of pressure-treated timber is quick to build and cheap. It suits light greenhouses on level ground. Fix it to the ground with stakes or ground anchors, and treat it so it does not rot.
Bare soil
Only small growhouses and polytunnels go straight onto soil. Polytunnel hoops go into ground tubes or are dug in, as the maker describes.
Anchor it
Wind is the biggest threat to a greenhouse in the UK. Bolt the frame to the base or use the anchoring kit from the maker. On an exposed site, choose a model with an anchoring system included. The Palram Canopia Glory, for example, comes with an internal anchoring system.
Check before you build
- The base must be square. Measure both diagonals; they must be the same length.
- The base must be level in both directions.
- Check the maker's base size, not the nominal size. A "6x8" greenhouse is rarely exactly 6 by 8 ft.
- Leave room around the outside to clean the glass and reach the gutters.
The base also affects planning permission: a raised platform over 0.3 m high is not permitted development in England. Back to the buying guide.
