Plastic Greenhouses and Growing Tunnels
Plastic greenhouses and growing tunnels can give an allotmenter a head start to the growing season.
The main advantage of plastic greenhouses is that they provide a quick and convenient way of creating a warm growing environment in early spring. The plastic captures the hint of the sun, and protects young plants from any chilly winds.
Growing tunnels have the added advantage of germinating your seedlings in situ, saving you the time and effort of needing to transplant them. This needs to be weighed against a trek to the allotment in late winter to erect the growing tunnel and the risk of being unsuccessful on securing germination in cold soil.
About Plastic Greenhouses
The best plastic greenhouses are a cheaper alternative to greenhouses, but they also have advantages in their own right:
- Plastic greenhouses come in smaller sizes than glass greenhouses
- They are easy to erect
- They are easy to take down
- You do not need to worry about building a firm base for plastic greenhouses (like you need for a glass greenhouse)
- There is no glass to break (and fall apart into your garden or allotment)
- Plastic greenhouses extend the growing season (especially early sowings) and can increase success with heat loving vegetables
Before purchasing a plastic greenhouse, you may like to consider their disadvantages:
- They can get damaged in the wind
- They typically use zip doors – and these can be fragile and break easily
- The plastic gets damaged by the sun
- Some designs of plastic greenhouses lead to water pooling on their rooves, and this weight can damage both the plastic and the supporting poles
My experience has taught me not to think of plastic greenhouses as a durable investment – rather a convenient one. The lifetime of the best plastic greenhouses can be extended by:
- Positioning in a sheltered spot
- Securing plastic greenhouses either by using wire or guy ropes and tent pegs
- Taking plastic greenhouses down at the end of summer to protect them from the winter elements
Depending on the weather and the quality of plastic greenhouse you buy, my suggestion would be to allow for a lifespan range from 1-3 years. Therefore the best plastic greenhouses may actually be the ones that you can easily, and cheaply, buy replacement plastic covers for.
If you are considering purchasing a plastic greenhouse, you may like to consider:
- The shape of the roof
Does it allow water to run off easily?
- The strength of the plastic
Is the plastic re-enforced, often with a woven green mesh stuck onto the plastic?
- Are replacement covers available?
This is actually a good aspect! Rather than a sign of sub-standard materials, expect to need to replace the cover of plastic greenhouses, and therefore investigate the ease and cost of doing this.
- The strength of the poles
The covers may be replaced, but the poles will not. Are the poles made out of strong materials?
- Shelving or racking
Does the plastic greenhouse come with shelving or racking? This can be helpful, especially in the spring for growing or hardening off seedlings
Does the growhouse come with guy ropes or tent pegs, or at least does it have the hooks to allow you to secured the greenhouse?
This may be obvious, but does the plastic greenhouse fit where you would like to place it?
About Plastic Growing Tunnels
There are actually three types of growing tunnel, or at least coverings of growing tunnels, each with their own advantages:
- Plastic or Polythene growing tunnels
These offer the warmest environment for seedlings and are ideal for spring germination in cold soil. The plastic traps the heat inside the tunnel, warming the soil and providing an ideal environment for germination. The narrowness of the growing tunnel means that there is no need to worry about watering the seedlings as the soil will naturally stay moist from rain on the surrounding ground. The biggest risk will come with the onset of warmer weather when the hot sun may potentially scorch the young plants.
- Fleece growing tunnels
Fleece growing tunnels may not be as warm as plastic growing tunnels but they have their own advantages. They will retain enough heat during the night to protect young seedlings from frost damage, whilst on hot days the fleece will take the edge off scorching sunshine. Fleece also allows air movement that helps keep the plants healthy and, if properly secured around the edges, will form an effective barrier against all sorts of insect attack.
- Net growing tunnels
These growing tunnels are more for protection than for extending the growing season. Netting comes in many grades and varieties depending upon its desired use, but on a growing tunnel its most frequent use is to protect against caterpillar or bird attack during late spring and summer growth. Netting will allow you to water the plants during the growing season and allow the plants to receive their full quota of sunshine.
Many of the buying considerations for growing tunnels are similar to those for plastic greenhouses. I suggest considering:
- Whether replacement covers are available
Spring and autumn weather can bring some of the most severe weather conditions and even the most durable covers can be damaged. You may also want to investigate whether the growing frame comes with a set of covers (plastic, fleece and net) so that you can change the cover as the growing season progresses.
Unfortunately it is not only your plants that will enjoy growing inside a growing tunnel. It is worth considering whether the design of the tunnel allows you to easily move the tunnel or access the plants inside for weeding. During the growing season, hoeing around the tunnel is especially important for net covers to prevent weeds becoming caught in the net. These can be hard to remove without causing damage.
The higher the growing tunnel the larger the plants you can grow within. Apart from the cost implication, a higher tunnel may also be more susceptible to weather damage.
These are ideal for large individual plants to protect them in the early stages of growth, for example squash, courgette, melon, and even tomatoes.
Plastic cloches can be very useful. It is important to make sure that their bottom edge is covered with soil. Without this, strong winds can blow them off the plot!