Polytunnels are structures covered in stretched plastic material, usually in a half-cylinder shape. They serve much the same function as greenhouses, protecting plants from winds, cold temperatures and many garden pests. However, their main benefit is creating a warm, humid environment, letting you grow delicate vegetables or plants out of season. Polytunnels are either walk-in types or low-style models less than 45 cm (18 inches) tall. Vegetables grow in both versions, but you can get a larger, more varied crop in a walk-in polytunnel.
Pick a polytunnel. Models range from lightweight garden to heavy-duty tunnels that require lots of manual labour and some engineering knowledge to construct. Beginners should opt for pop-up or easy-build polytunnels. Prices range from around £40 to many thousands for the larger versions.
Build your polytunnel on level ground in a spot that gets a lot of sunlight. Watch out for tree or wall shadows if placing at the edge of your garden.
Map out a plan of your polytunnel ground space. Calculate how much room you have for pots or raised beds. For example, you'll want a walkway in the middle at least 90 cm (3 feet) wide to access and prepare growing areas.
Decide how you want to organise your polytunnel. Install shelves if you want to grow lots of smaller vegetable crops such as lettuce, radish and cress. Use ground pots, grow bags or raised beds for tomatoes, beans and other climbing or tall vegetables.
Choose the right type of vegetable seed. Select vegetables that won't grow well outside, or varieties that you want to keep growing long after the season is over. Tomatoes, mangetout, aubergine and carrots all grow well. Avoid cool weather vegetables such as kale, broccoli and spinach.
Plant your seeds as instructed on the seed packet. For example, you can plant tomato seeds directly into flattened grow bags in a polytunnel. Spray your seeds with water using a mist sprayer. Don't use a heavy hose or watering can in the polytunnel. Plants will generally require less watering.
Install a thermometer to check temperatures in your poytunnel. During summer, temperatures can reach levels that can destroy plants. Try to maintain temperatures of 20 to 25 degrees C (68F to 77F) by opening polytunnel door flaps and installing a fan if needed.
Water your vegetables frequently, but do not allow the soil to get waterlogged. Harvest vegetables when they're ripe and plump.
Choose your vegetables based on how difficult they are to grow outside, and how expensive they are to buy in shops.
Pinch off yellowing or brown leaves from plants. These may be dying or infected with fungus.
Watch out for too much humidity in your polytunnel. This can cause diseases to spread.
Water plants if the leaves start to curl inwards.