The Ultimate Guide to Greenhouses

If you love growing fresh fruit or veggies in your garden but feel limited by the growing seasons, you may want to invest in a greenhouse. Greenhouses allow you to extend the growing seasons and can help you grow crops all year round. Here, you’ll find everything you need to know about greenhouses including how they work, what to grow and how to choose the ideal one.

How They Work

Greenhouses work simply by light being converted to heat. When plants absorb sunlight in the greenhouse, they convert it to heat energy and release the heat into the greenhouse. The glass or plastic sheeting that makes up the greenhouse allows light rays to enter the structure where they are absorbed and converted to heat. The heat that is released by the plants is trapped by the glass causing the greenhouse to remain warm.

Different coloured plants will respond differently to the sunlight. For example, darker coloured plants will absorb more light and therefore will become warmer, and lighter colours will absorb less light and reflect more meaning they don’t release as much heat.

There are 2 reasons why greenhouses maintain heat:

  1. After an object absorbs light energy, the heat energy is released very gradually meaning it continues giving off heat for longer
  2. The heat energy cannot pass through glass and plastic sheeting easily. It, therefore, gets trapped inside the greenhouse

Can You Manage the Temperature of a Greenhouse?

For your plants to remain happy and healthy in your greenhouse, they must be in a suitable living environment. Having high levels of humidity or if the temperature of the environment is too high or low can result in stressed plants that are more prone to mould and mildew.

To control the temperature and humidity levels of your greenhouses there are a few methods:

Fans

Fans can be used to promote consistent air movement in your greenhouse. A horizontal airflow fan (HAF) can be mounted on the roof and sides of the greenhouse as a cost-effective option that helps keep your crops growing. Alternatively, an extraction fan will cool down the greenhouse by drawing air from the outside and exchanging it with the air inside the greenhouse which will keep the interior cooler and reduce humidity.

Wet Walls

To lower the temperature of the greenhouse, you can use the wet walls method which uses a gutter at the top where water trickles through to the wet wall to a collection pipe. This water then goes through a refiltration system and is recirculated. By using a combination of a wet wall and an extraction fan, you can cool your greenhouse down by 10-15 degrees.

Vents

There are two commonly used types of vents: roof vents and side vent walls. Roof vents are a passive cooling method that uses natural convection of hot air. Side vent walls can be used to protect plants whilst increasing the airflow within the greenhouse. When choosing a vent as your temperature control solution, ensure that you have a weather station to monitor the temperature, humidity, solar levels, wind and rain.

Shade Cloths

Control the level of exposure that your plants have to solar energy with shade cloths. These are curtains that roll out over the greenhouse to protect your plants from burning from the rays. There are two types of shade cloth: knitted and woven. Knitted shade clothes last 7-10 years whilst woven last 10-12 years. Woven is also 30% heavier and tends to be more expensive, however, both types of shade cloth are UV resistant and can withstand extreme sun exposure.

Radiant Heating

Radiant heating systems work by radiating heat from a hot surface to cooler surroundings. In a greenhouse, piping is installed beneath the foundation which is connected to a water heater. When the hot water travels through the piping, the air between the greenhouse floor and the structural foundation is heated, and as we all know – heat rises.

Benefits of a Greenhouse

Protect Your Plants

Greenhouses make the ultimate shelter to protect your plants against harsh weather conditions and pests. With the temperamental weather in the UK, it makes sense to invest in a greenhouse so that your plants have a stable climate to grow in throughout the seasons.

Avoid Pesticides

The enclosed space for your plants means that you don’t have to spray harmful chemicals onto your plants to protect them from pests. Therefore, you can enjoy pesticide-free food that is healthy and safe.

Garden Throughout the Seasons

To make sure you can enjoy your summer foods all year round, a greenhouse is an ideal solution. Greenhouses allow you to start your growing season any time of the year and have control over what you grow and when.

More Growing Options

Because you can control the temperature and humidity of your greenhouses, you can grow a bigger range of fruits, vegetables, flowers and exotic plants. A greenhouse gives you the freedom to grow whatever you want, as long as you understand the environment your plants need to grow, the choice is yours!

What You Can Grow in a Greenhouse

Greenhouses are ideal for growing a range of plants all year round. However, especially if you’re new to gardening, it can be tricky to decide the best things to grow. Here are the easiest and most common crops to grow in your greenhouse:

Chillies

Chillies are perfect for small spaces and are super easy to grow in a greenhouse. They thrive in bright light and warm temperatures and so are an ideal option for your greenhouse.

Tomatoes

Another greenhouse favourite for many gardeners is tomatoes. Growing your own tomatoes can result in delicious crops that offer a longer growing season than those grown outdoors. There are different varieties, but it’s best to start with the bush variety as they are better for beginners.

Cucumbers

Cucumbers are a great vegetable that is perfect for summer salads. Homegrown cucumbers are delicious and provide a refreshing addition to your kitchen. They’re also space-saving as they are grown upwards so are perfect for smaller greenhouses!

Potatoes

One of the best crops to grow all year round. Potatoes started in early Winter will be ready to enjoy by March. Potatoes are enjoyed all year round so make a perfect choice to start growing at any time.

Peas

If you sow your peas early enough, they will be ready for eating by early spring. Peas are easy to grow and highly nutritious making them a perfect addition to any gardener’s greenhouse. 

Cabbage

Cabbages are a greenhouse favourite as they’re rich in vitamin C and antioxidants and are a perfect ‘cool season vegetable. They’re extremely easy to grow making them ideal for beginners.

Downfalls to Owning a Greenhouse

It’s Expensive

Greenhouses not only have a high upfront cost, but they also cost a lot to run. Depending on the style, type and size of greenhouse you are considering, you could be spending hundreds or even thousands of pounds throughout the year. You may also need additional purchases such as temperature control solutions and gardening supplies.

Pests & Disease Can Spread Rapidly

Although a greenhouse is great protection against external threats, if threats do find their way into the enclosure, pests and diseases can spread more rapidly which can affect your entire crop. Therefore, more proactive approaches will be required to prevent this from happening.

High Maintenance

Because the temperature of a greenhouse fluctuates throughout the day, you will need to closely monitor the temperature of your greenhouse otherwise you are putting your plants at risk of experiencing temperatures they can’t survive in. You will also need to constantly monitor the hydration levels as the soil tends to dry out more quickly in warmer environments.

Lack of Pollination

Some plants rely on pollination to thrive. However, in a greenhouse, their pollination requirements are not met due to the lack of bees and wind. This means intervention may be required to ensure pollination takes place. You can do this by using a paintbrush or cotton swab to transfer pollen or by gently shaking or tapping flowers.

Lack of Space

A greenhouse can take up substantial space in your garden. Before purchasing your greenhouse, ensure you can easily fit one in your garden whilst still having space for your family to be able to enjoy the garden too.

How to Choose the Best Greenhouse

Depending on your experience level may determine which greenhouse you go for. If you’re just starting out in gardening, the first rule is to buy as large a greenhouse as you can afford and have space for it. Ideally, an 8ft x 6ft greenhouse would give optimal space for a beginner, but smaller is fine. Here is a quick guide to buying a greenhouse whether you’re a new or seasoned gardener:

  1. Choose the size of your greenhouse. Greenhouses come in a range of sizes in 2ft increments. The most popular size is at least 6ft wide so that you have enough room doe shelves on both sides that also allows you to move around freely.
  2. Choose the shape of your greenhouse. You can choose from three main shapes of greenhouses: traditional, lean-to and round. You can also get newer dome shapes too!
  3. Decide on timber or metal. Metal greenhouses are usually cheaper and have lower maintenance, however, timber is a popular choice as it’s more attractive and is better at maintaining a constant temperature.
  4. Choose your glazing. There are different types of glass available for your greenhouse. Horticultural glass lets in the most light and is long-lasting. Toughened glass is more expensive but shatters more safely so perfect for homes that have kids or pets.
  5. Choose ventilation. Ventilation is essential, especially in summer. Ideally, you’ll need two hinged roof vents and a side vent, but this depends on the size of your greenhouse.
  6. Decide on the flooring. A firm-level floor like paving slabs or gravel makes easy access and drainage. It can also be wetted down in summer to keep the air humid.

Greenhouse FAQs

Will greenhouses stay warm in the winter?

Yes, you can keep your greenhouse warm in winter by using insulation material or heating solutions to keep your plants in their ideal climate.

Are greenhouses waterproof?

No greenhouses are 100% waterproof as water can come in under the bottom or may find a way in through a leak. It’s therefore important to make sure there is somewhere for the water to escape naturally.

Are Greenhouses Sustainable?

It’s hard to determine exactly if greenhouses are good or bad for the environment, however, they do not need to run on electricity and can instead utilise thermal energy which will consume less power.

Some greenhouses are fuelled with artificial heat which contributes to the pollution of the atmosphere. If a greenhouse isn’t powered by artificial heat, it’s practically harmless to the environment. If you are currently using an artificial heat source, maybe you can replace this with the sun’s natural rays.