Greenhouses buying guide

Greenhouses

Greenhouses open up a whole new world of possibilities in your garden. They offer a protected growing environment for tender plants and seedlings, letting you extend the growing season and enjoy homegrown fruit and vegetables for longer. But what do you need to consider before buying one? With such a wide variety of shapes, sizes and types on offer, check out our essential guide to finding the right greenhouse for you.

Select a style

Before you go any further, ask yourself two questions: how much space do you have available and what would you like to grow? If you have plenty of room in your garden and/or would like to grow a wide range of plants, a traditional greenhouse with an apex roof is right for you. Height matters: the taller the eaves, the better the light transmission, so look for a greenhouse that’s at least 1.5m tall. The downside of a large greenhouse can be the cost of heating it during winter.

If you have limited space in your garden, or would prefer to keep your lawn clear, a lean-to greenhouse could be the answer. They are designed to stand against a wall or fence and cost less to heat than all-glass models. Be aware, though, that south-facing positions can result in overheating whilst a north-facing lean-to greenhouse may not get enough sunlight.

Is your garden too compact? Are you not sure you need a greenhouse all year round? Consider an alternative such as a polythene greenhouse , which doesn’t need a base and can be folded away, or a space-saving mini greenhouse (which opens at the front and is ideal for summer crops) or a budget-friendly cold frame (a box with a sloping glazed lid) is great for sowing seeds that need cool conditions.

Decide on position

You should site your greenhouse where it gets maximum sunlight and avoids shadows from neighbouring buildings or trees. Positioning it close to your home will make it easier to access power for lighting and heating. If you can, orientate your greenhouse to fit your growing needs: east-west will slightly extend light levels during winter whilst north-south is best for summer crops such as tomatoes.

Measure out the base

If you’re going for a traditional or lean-to greenhouse, you’ll need to install a perimeter base plinth, using bricks or steel reinforcements. To visualise how much of your garden a greenhouse will take up, measure out the base on the ground with some bamboo canes or string.

Do you need to get your wheelbarrow in and out of your greenhouse? Check door and internal dimensions are adequate. You’ll also want to stand up and move around inside comfortably, so check the height. Have you got plenty of easy access for carrying tools and trays of plants to and from your house, garage or shed ? Walk between your existing buildings and the imaginary doors of your new greenhouse to check.

Choose your glass

You’ll need to decide which of the three main types of glazing suits you best:

  • Standard horticultural glass: standard horticultural glass is crystal clear, lets 90% of light through, doesn’t degrade in sunlight and it reflects heat back into the greenhouse. The downside is it can be tricky to clean and may potentially crack in extreme frosts.
  • Toughened glass: toughened glass is crystal clear, safer than standard glass because it will crumble instead of splintering, it’s great for doors or anywhere people may fall onto the glass. It is however more expensive than standard glass.
  • Polycarbonate safety glazing: polycarbonate safety glazing provides better insulation because two sheets of polycarbonate acts like double glazing. It’s shatterproof and stronger than standard glass. The downside is that it only lets 83% of light through, it’s harder to clean, may discolour in sunlight, it’s unstable in high winds and less visually pleasing.
  • Ventilation: ventilation is very important – look for greenhouses with roof vents, which should ideally be on both side of an apex roof, as well as side vents. Louvered vents are good at regulating airflow but can be hard to draught-proof in winter.

Add finishing touches

Once you’ve got your greenhouse up, make the most of the internal space with multi-tiered shelving, staging and potting benches. Place a water butt nearby for an eco-friendly supply and think about installing a heater. Use a thermometer to check temperatures: a minimum of 7C (45F) is recommended to sustain tender plants over winter. Now it’s time to fill your greenhouse with pots, troughs, seed trays, growbags, plug pots and hanging baskets – and get growing.

Expert tip

“Don’t allow the temperature inside your greenhouse to rise too high or drop too low. In summer, apply a shade paint to the outside of your greenhouse and open doors and vents to increase airflow and reduce heat levels. In winter, clip a layer of horticultural bubble wrap inside your greenhouse frame to reduce heat loss and block cold draughts.”

Jonathan Clark, Tesco Garden buildings & structures buyer

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