How to choose a greenhouse

The seven decisions that narrow the choice

A greenhouse is not useful simply because its nominal size fits on a sketch. It has to fit the real garden, accept the plants you want to grow and remain accessible when those plants are at full size. Work through the decisions below in order and most unsuitable models will disappear before price becomes the deciding factor.

1. Decide what the greenhouse must do

List the jobs you expect it to handle during a full year. Seed raising needs clean shelf space and easy access to trays. Summer tomatoes and cucumbers need height, ventilation and floor-level rooting space. Tender plants overwintered in pots need clear floor area and a route wide enough to move them. A place that is pleasant to work in needs more aisle width than a structure used only for propagation.

A compact growhouse can outperform a cramped walk-in when the main job is protecting trays and small pots. Conversely, shelves alone become restrictive once vigorous crops reach the roof. Choose the growing format before choosing the exterior style.

2. Measure a usable site

Mark the exact published base dimensions on the ground with string or masking tape. Then add the approach to the door, room to open or slide it, space to clean the glazing and enough level ground to assemble long frame pieces. Keep gutters, downpipes, drain covers, fence posts and low eaves in the plan.

The nominal label is only a category. Two products described as 6 × 4 can have different base and overall measurements, so foundations should be set out from the technical drawing for the model you actually buy.

3. Choose the right format

Freestanding apex greenhouses offer light from every side and the most familiar walk-in layout. A 6ft width normally allows a central path with narrow staging or beds, although the exact internal width is smaller than the external label.

Lean-to greenhouses use a long wall and project less into the garden. The wall affects fixing, shade and heat, so it must be treated as part of the structure rather than convenient scenery.

Mini greenhouses and tall wall growhouses protect plants without a standing aisle. They are efficient on patios, balconies and narrow side returns, but their shelf arrangement dictates which plants fit.

4. Compare glazing honestly

Toughened glass is clear, relatively heavy and breaks into smaller pieces than horticultural glass. It suits buyers who value a traditional appearance and straightforward cleaning. Large panes still need careful handling and a square, stable frame.

Polycarbonate is lighter and shatter-resistant. Twin-wall panels diffuse light and add an insulating air layer, while clear single-wall panels preserve outward visibility. Check how panels are retained, particularly on exposed sites, and follow the manufacturer's anchoring requirements.

Acrylic and styrene are common on compact timber growhouses. They reduce the risk associated with glass in busy patio spaces, although scratch resistance, clarity and panel retention vary by design.

5. Check doors, vents and working height

Door width matters when carrying trays, compost or large pots. Check the clear opening, not simply whether the door is single or double. Sliding doors do not swing into a narrow path; hinged doors need a clear arc and a way to secure them in wind.

Ventilation should be planned before planting. One roof vent may be adequate for a small structure in mild conditions but cannot guarantee safe summer temperatures. Look for a usable door, opening roof vents and a route for low-level replacement air. Automatic openers can help, but only when compatible with the vent and correctly adjusted.

Eaves height affects comfort and crops near the sides. Ridge height alone can make a greenhouse sound spacious even when the useful shoulder-height zone is narrow.

6. Understand the base and anchoring

Every greenhouse needs a level support that will not twist as the ground moves. An included metal perimeter base is helpful, but it still needs secure fixing to the prepared site. Optional bases should be priced before comparing totals. Timber structures without floors need support that keeps the frame square and avoids persistent contact with wet ground.

Paving is clean and reversible; a perimeter foundation can leave soil beds inside; concrete is robust but permanent. Whatever the material, drainage and anchoring are part of the same decision. Read our greenhouse bases, positioning and installation guide before preparing the site.

7. Budget for the working greenhouse

The complete cost can include a base, anchors, staging, extra vents, automatic openers, water storage, delivery restrictions and professional help. It is usually better to buy a slightly simpler structure with a properly prepared base than to spend the whole budget on the frame and improvise the foundation.

A quick route to the right size

• Choose a mini growhouse when you mainly need protected shelves and have less than a metre of depth.
• Choose a 4 × 4 lean-to when a compact walk-in is more useful than long shelving and a suitable wall is available.
• Choose a 6 × 4 freestanding greenhouse when you want a central aisle and a small conventional footprint.
• Choose a 6 × 8 greenhouse when you can keep the extra length accessible and expect to combine staging with tall crops.
• Choose an 8 × 4 lean-to when wall length is available but projection into the garden is limited.

For a more detailed measurement method, continue to what size greenhouse do I need?. If this is your first installation, use the first greenhouse checklist before ordering.

Final checks before buying

Confirm the exact base and overall dimensions, package sizes, access route, door opening, vents, included base parts, anchoring method and replacement-panel availability. Read the assembly manual for the precise variant, because glazing and frame options within one product family can change the installation sequence.

The best greenhouse is the one that fits the whole working zone, supports the crops you will actually grow and can be safely maintained for years—not simply the largest nominal size that can be squeezed between boundaries.

The RHS greenhouse-selection guide is useful independent background to the format, frame and glazing decision. For a shortlist after those checks, compare recommended UK greenhouses rather than selecting solely by the nominal size.