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We discuss how to build a greenhouse and the best DIY tips to follow. We also included contractors’ costs and free quotes.
Many people have gardens where they grow food crops or flowers for harvesting in the summer. Unfortunately a scarcity of warm weather or too much wet weather can completely decimate crops by just not giving them enough sun or warmth to ripen properly. The answer is to provide an indoors shelter which allows the plants to have as much sunlight as possible while protecting them from the elements. This is where the greenhouse and its many variants become indispensable to the gardener and their crops.
Today’s article will try to focus your thoughts on
A traditional greenhouse, sometimes known as a glasshouse, came about from the need to give young plants a head start in the growing season. There are many days in early spring when the days are bright and sunny yet too cold for young plants to be exposed to the unprotected air and wind. Night time especially can still have frosts until late spring especially if the skies are clear. All of these can slow the growth of a young plant and seriously inhibit its ripening later on in the season. For this reason you need to have an enclosure which will protect the young plant from cold winds and frosts while allowing sunlight to be harvested by the plant.
The obvious answer to this problem is to use glass as the transparent protection for the young plants, and indeed this material was used from the time when glass began to be made commercially. Originally, because it was so expensive, the only people able to afford large quantities of glass were the wealthy landowners. In a time when everyone grew the majority of their own food, being able to serve and eat exotic fruits and vegetables were a sign of wealth and status. Whoever could afford glass had various greenhouses devoted to growing not only exotic plants but also extending the growing season of more mundane home-grown food plants.
In all the time that greenhouses have been around, there have been two basic types:
Unheated greenhouses concentrated on giving the plants grown locally as long a growing season as possible by protecting the baby plants and seedlings from cold winds and frosts. This type allowed seeds to be planted in trays and pots and germinated in a sun-drenched position.
Once the plants had grown to be more hardy and the cold nights had finished for the year, these plants would then be planted out in the garden to give them the space or height needed to grow to their full potential. Because they had a head-start and were able to germinate early in the year, they were also able to produce fruit and ripen while the days were still long and hot.
If you wanted to produce more exotic plants more suited to tropical conditions you had to provide some way of heating the enclosed space as glass is not the best type of insulator available. This led to the concept of having a heated greenhouse. Some greenhouses had furnaces situated in the greenhouse itself while others had furnaces elsewhere and ran steam pipes through the greenhouse. The advantage of using hot pipes was that they could be buried in the soil to warm the ground enabling quick and early germination of seedlings as well as providing hot humid environment for the tropical plants. Another way of providing heating was to install in the greenhouse a working compost heap.
Compost when undergoing the transition from garden debris to usable compost produces a lot of heat which can be used if done properly. Many British stately homes had greenhouses producing pineapples and bananas by using heated growing beds. These fruits would have been displayed and offered to their guests at expensive dinner parties to enhance the landowner’s reputation. Even relatively easy subtropical plants such as orange and lemon trees were very common. At a time when the nearest source of citrus fruits was from the Mediterranean countries at great expense, this would have been something to be proud of.
Some forward thinking people realised that they could use this warmth to increase their quality of life in an era before central heating. They built sunrooms onto their houses incorporating growing areas for subtropical plants. These became known as ‘Orangeries’ for obvious reasons, and it was fashionable to take tea or coffee with guests in the warmth of their ‘Orangery’. In fact many species of exotic orchid were grown and made widely available from these warm sunrooms.
As glass became cheaper, so the unheated variety of greenhouse became more universally known and was eventually used by the less affluent middle and working classes. It was soon realised that any size box with a cover could be made out of glass so seedlings that had been germinated and raised in a greenhouse were planted in the ground and temporarily sheltered by a small glass structure known as a cloche or a coldframe. This process became known as ‘hardening off’ and was essentially a method of getting a plant used to the open air and the temperature differences away from the greenhouse.
The only real problem associated with these early greenhouses, cold-frames and cloches was that they were made from glass and were therefore very brittle and very heavy. The brittleness of glass also meant that there had to be large amounts of wooden supports and small panes of glass. Let’s face it; glass greenhouses were dangerous especially if you had strong winds, heavy snows or small boys with soccer balls. They were easily broken.
The rise of the new plastics technology at the end of the twentieth century provided an acceptable and safe alternative to glass. Rigid transparent plastics such as polycarbonate provided double and triple glazed versions suitable for large expanses of lightweight roof and wall panels. Flexible polyethylene sheet allowed large areas to be covered essentially making transparent plastic tents. This evolved into the modern polytunnels which are used to such great advantage by horticulturists, market gardeners and homesteaders. It is not unusual to have polytunnels up to 100 yards long providing sheltered growing areas for fruit, vegetables and flowers.
We now have small solid greenhouses suitable for small gardens made of safe lightweight materials such as polycarbonate while large plant wholesalers and homesteaders have huge flexible polytunnels made from polyethylene sheets. Both these materials are cheaper to buy than glass, safer as a construction material and safer to use as plant protection with humans around.
The double and triple glazed polycarbonate sheets also trap sunlight and warmth allowing you to have a heated greenhouse using solar power only.
Ok. We have now got up to today’s situation. You now know a bit about how greenhouses came about and why they are constructed from certain materials. I would not advise anyone to build a green house from glass (unless you buy a kit, with glass included). Always use polycarbonate sheets not only for convenience in cutting to size and safety but also for the lower costs involved in buying and fitting.
First of all let’s think about how you can build a greenhouse yourself. We won’t talk about upcycling yet, we’ll do that later on, but for now we can talk about buying new materials. The types of materials you need to construct a greenhouse fall into five categories
The base can be either a hardstanding such as concrete and paving slabs or soft such as gravel and soil. The advantages and disadvantages of these are as follows:
Concrete bases allow you to fix your greenhouse to a firm base in case of strong winds and also allow you to have a level base. The lack of loose earth means that you can be inside in all weathers and not have to cope with muddy ground. The plants will have to be planted into trays, pots and containers of all types giving you independence when it comes to moving plants outside. It also means you can give different plants the soil types they prefer. Because the plants have no contact with the ground, you will have to ensure that they are properly watered and fed.
Concrete foundations provide a a strong level perimeter strip with a soft inside area. This combines the advantages of concrete hardstanding and soft inside material.
Paving slabs give you the advantages of concrete while also allowing you to lift pavers to expose ground and planting areas. You can easily dig fertiliser into the soil to increase the fertility and you don’t have to worry as much about watering the plants as they are in contact with the outside water- table. The positions of the pavers can be changed to suit the different types of vegetation you have planted and you can make dry paths around the plants. You are limited to the area of a paver as the minimum planting area or minimum walking area.
Laying gravel allows you to define planting areas and walking areas with the ability to change if required. Gravel is relatively cheap compared to pavers and if dug into the soil, can improve drainage. Gravel and no-gravel areas can be as large or as small as required although in practice the minimum practical width of a path would be about 18” wide.
Having the greenhouse floor as soil allows you to plant anywhere, although in practice it would be better to segregate planting areas and walking areas. The soil will become hard packed where the walking areas are but can become muddy if the ground outside becomes waterlogged.
The ideal choice for a greenhouse base is to have a raised concrete strip foundation defining the perimeter to ensure the structure is level and above ground which will ensure the structure avoids flooding inside. Inside the structure you can define soil areas using wooden boards so the soil can be banked up inside, with no mixing between soil and gravel or undermining of pavers.
Fitted to the raised concrete foundations we have a wooden beam made from treated 4” x 2” or 4” x 4” sawn timber bolted to the concrete. The wood is joined at the corners with a simple half-lap joint to ensure the shape stays at the shape required. Perhaps we should say a bit here about the shape of the greenhouse. The floor shape (footprint) can be any that you desire but bear in mind that certain footprints make it easier to build the structure; rectangular and square being the most obvious ones but in certain circumstances circular footprints can be used as well. We will talk more about this later.
This is the part of the greenhouse which defines its finished three dimensional shape. Depending on the materials used this will define the variations in shape you have available. If you choose wood or bamboo materials to make this structure you will have to define the shape in a series of flat planes and straight lines. If you produce quadrilateral shapes such as rectangles or squares then you will end up with the traditional greenhouse shaped structure. If you want to produce a geodesic dome (look up the definition in Google) then you will need a series of identical triangular shapes fitted together.
If you use flexible plastic or metal materials flexible enough to have both ends in contact with opposite sides of the perimeter framework then you can construct half hoops which when covered will produce shapes reminiscent of half cylinders lying on their side. Old (or new) alkathene water pipe can be used to provide a flexible half hoop suitable for building a polytunnel type greenhouse. There are many websites giving plans for home-made greenhouses and I leave it to you to choose one yourself. Here is an example of a method to build a polytunnel:
Rigid and semi-rigid. If you choose to use a rigid or semi rigid material such as glass, double or triple walled polycarbonate sheets or single wall corrugated polycarbonate sheets then you must have a framework constructed of flat planes (with the exception of single skinned corrugated polycarbonate which has limited flexibility in the direction which makes the corrugations horizontal. There is enough flexibility to bend corrugated polycarbonate around the hoop supporting framework. Unless you have laminated or artificially strengthened glass the panes of glass will have to be small, meaning panes of no more than 18” x 12”.
Glass will have to be fitted into rebated frames with a padded adhesive such as putty or silicon mastic with a wooden bead to keep the glass in place. Polycarbonate sheets can be drilled and screwed on the surface of the frame (or in rebates) using rustproof screws and flexible spacers and washers. The spacers and washers are used to prevent cracking of the brittle polycarbonate if the screws are tightened too much. If you decide on glass as the covering material then you will need a rebate in each frame in which to seat the glass pane as you will not be able to fix through it. Any rigid plastic material can be drilled and screwed with normal rustproof screws and flexible washers.
Flexible. A flexible covering such as polyethylene film can be unrolled over the supporting framework and stapled into position temporarily followed by rigid battens. This effectively sandwiches the film between the framework and the battens so the film will not tear and work loose.
You will always need some way of entering and exiting the structure so doors are required. It is better to have a doorway at either end so that in extremely hot weather you can open both doors to take advantage of a through draught. You should also allow pollinating flying insects access to the plants so they can do their job.
Windows are useful in the roof if you want ventilation and the ability to remove hot air from inside while still retaining security and preventing land based insects, animals and humans from accessing your produce. If you are building your own then doors and windows can be simply made by covering a wooden frame the size of the opening with rigid polycarbonate. Fix the door or window to the frame using a pair of hinges. Don’t forget to put a lock or a padlock on the door to safeguard your crops when you are away.
What accessories can you have with a greenhouse? Simple really, but you will have to run electricity and water to the greenhouse first. Remember that if you are running electricity outside you will need external grade switches and power sockets as well as a separate circuit breaker. Some ideas for accessories include:
If you aren’t particularly worried about your greenhouse looking perfect or if you want to be seen to be helping the environment as well as saving those precious dollars, it is quite easy to substitute someone else’s waste into useful bits and pieces for your greenhouse. If you have a bit of an artistic flair then you can make some really quirky greenhouses that can look better than bought ones.
Pallets. Wooden pallets that are used for carrying goods transported by truck can be very useful. Do not just take them if you see them lying around. They belong to someone and cost money. If you know of a haulage company or supermarket that has any broken pallets, they will usually give those away as they are no good for anything. When you get them home they can be used for many things.
Second hand windows. It is possible to build a complete greenhouse using second hand or reject windows. Contact a double glazing company and ask if they have any old windows they have taken away from a job that are destined to be thrown away. If you can only get hold of a few then build a set of cold frames instead.
Clear plastic disposable water bottles. A clever way to build walls for your greenhouse is to collect clear plastic water bottles, remove the caps and cut off the bottoms. Thread them onto bamboo canes the height of your walls. The bottle walls will allow light through yet insulate your plants from the cold. To make a greenhouse 6ft x 8ft area and 6ft high you will need approximately 1,500 x 2 Litre plastic bottles and approximately 140 x 6ft garden bamboo canes. Make wooden rectangular frames onto which you can staple the canes and screw the four wall panels together to make a box. To make a roof, simply cut the bottles lengthways in half. By fixing the half bottles onto wooden battens the length of the pitched roof, you will have a plastic roof able to collect rainwater.
‘Bubble wrap’ packaging material. The common packaging material consisting of two layers of polyethylene sheets with air bubbles between can make a good insulation material for your greenhouse panels. You can collect second hand packaging or buy a 50yds roll at very cheap prices and at different widths.
There are just a few simple rules when you are upcycling and making things from someone else’s waste.
1. Don’t scavenge from private property unless you have permission.
2. Don’t use unsafe materials when building your greenhouse.
3. Don’t make a structure that is unsafe.
4. Don’t create more waste than you are reusing.
5. The finished article must have a function.
6. Use the materials you are recycling in as close to their original form as is possible.
There are many other ideas for upcycling in and around the garden. Just look online.
Building your own greenhouse from new materials or upcycled materials to your own design can be extremely satisfying but will take time. And that is something that most of us haven’t got a lot of. Even if you hire a professional to build one to your specifications, it will take longer and may work out more expensive than buying one either as a kit or from a greenhouse manufacturer and installer.
This is where a bought greenhouse comes into its own. You can buy relatively modest greenhouse kits which come as a collection of ready-made panels for walls, roof, door and gable ends into which you fit panes of glass or polycarbonate. All that is required is for you to supply a level base of the correct size and a perimeter framework made from treated timber onto which the panels are screwed. The finished structure will probably have a footprint of about 4ft x 6ft or 6ft x 8ft, being 8ft high at the roof’s highest point.
If your budget or your available space is not big enough for something of this size then you can buy for a few dollars a tiny greenhouse made of rigid plastic framework covered in a transparent polyethylene cover with a detachable front (this is also its door). The smallest one like this is approximately 3ft wide x 18” deep x 5ft high. It is obviously not designed as a walk-in structure but can be regarded more as a three shelf unit with a clear plastic cover. These work best if fixed to an existing wall such as a shed or garage to provide support or they can easily blow away.
These are ideal for bringing on trays of seeds or providing shelter for more established plants from cold winds.
If you have a large amount of available space (and a corresponding budget) then you can have either a solid greenhouse or a polytunnel made from standard sections to the size you want.
Really there is a greenhouse to fit all spaces and all budgets depending on your requirements.
With so many different sizes, shapes and construction materials available the ordinary gardener may become confused when trying to decide which one to buy. Here are some questions to ask yourself to clarify in your mind what exactly you want:
1. Size. Are you a starter or a grower? What exactly is your own personal vision? Do you enjoy outdoor gardening and all you want is somewhere to germinate and grow a few seeds from scratch so they have a head start before spring arrives? If so then all you will probably need is a ‘starter’ greenhouse with a potting bench, some soil and some seeds. Away you go!
Perhaps you are a gardener who likes to grow everything from seed or produce a selection of vegetables and flowers not usually possible in your local environment. You will need a structure big enough for your plants to grow and expand to their full size, bear fruit or blooms under carefully controlled environmental conditions. In this case you will require a ‘grower’ greenhouse with more room and possible different glazing specifications. You might need heating and ventilation as well. With some planning and ‘green fingers’ you could stock a stall at the local farmer’s market with fruit and vegetables months before their outdoor versions are even ripe.
If you just want something small to protect your outdoor plants from cold winds or frost until the days warm up then maybe all you need is a ‘coldframe’. These are simply boxes with a bottom that is open to the ground and a top that has a hinged transparent lid. You can carry it around the garden and put it where most convenient or over whichever plant needs protecting. Coldframes and cloches are small, unobtrusive and do not require building consent, foundations or permits.
Let’s ask the question “How big is big enough?” The smallest walk-in greenhouse has a footprint of about 4ft x 4ft. While a large one can be about 20ft x 16ft or even larger, suitable for a small commercial operation.
Always buy the largest greenhouse your site and budget can afford.
2. Choice of opaque or transparent glazing. When you choose your brand new greenhouse you will usually find you have a choice of clear,
opaque or semi-opaque panels. The different opacity determines how much sunlight your plants will get.
a. Clear panels. These are designed specifically to favour seeds and seedling growth. Your seedlings will grow quickly and have a strong, energetic start in life. These panels are usually made from glass or single walled polycarbonate.
b. Opaque (or diffused) panels. Plants that are being grown to maturity usually prefer diffused light. They achieve optimum photosynthesis and grow into a better shape and form. They become more compact and sturdy rather than spindly and tall from reaching towards direct sunlight. Panels made from multiwalled polycarbonate and polyethylene provides a good diffuse light.
c. Semi-diffuse panels. As you might expect, this is a compromise between the clear and opaque panels. Sometimes you can have an opaque roof with clear sides. This will allow more light into the greenhouse when the sun is at its lowest in the sky such as spring and autumn.
If you don’t actually know which type of panel you need or you want to play it safe because your requirements might change in the future, you can always just buy a greenhouse with clear panels and either paint the transparent material with white emulsion paint or drape some horticultural fleece across the windows. Either method will provide a temporary opaque panel which can be easily changed as your needs change.
3. Insulation. If you live in a zone which has snow and ice as part of your winter weather, then you will want to have some kind of insulation to keep your plants warm and cosy. Multiple walled polycarbonates are the greenhouse equivalent of home double and triple glazing. Twin walled polyethylene is also a good insulator but has more flexibility than polycarbonate allowing you to insulate polytunnels and domes. You will also have to consider snow accumulation on the greenhouse roof. Choose one with an appropriate snow-load rating to prevent collapse after a heavy snow fall. If you are building your own, make the pitch (angle) of your roof steeper to allow the snow to slide off.
If your winters are mild and you are simply looking for a ‘warm season extender’ then insulation is not so crucial. Single wall polycarbonate is perfect for this as is glass, but the fragility of glass can become a problem in hailstorms or windy weather when branches fly around. The most economical is polyethylene sheeting but you will have a limited lifespan of a maximum of about 5 years before the ultraviolet light degrades the polyethylene, so you will have to factor in the extra costs of replacements.
4. Your location and landscape. Mark on the ground with string and stakes where your greenhouse is going to be located. See how this will impact on not only your views, sight lines and outdoor activities but also your neighbours’ views. Consider the prevailing weather and wind. Maybe you can use an existing wall or line of trees to provide shelter from the wind, but make sure it isn’t always in shade or your greenhouse won’t be trapping the sun’s warmth.
Find out about your local zoning regulations. Some new developments require you to ask permission before erecting a greenhouse and other areas may impose restrictions on footprint size or height. If that is the case then maybe a smaller greenhouse (or two) will get around any restrictions. You might even be able to convince the planning office that your greenhouse is storage shed and get around the restrictions like that. If your greenhouse is a ‘lean-to’ type and fixes onto the side of your house, then the structure may be classed as an addition. This will attract even more regulations and restrictions so check beforehand and be sure of your facts. Be aware also that a greenhouse attached to your house with an adjoining door will increase the humidity indoors and may cause excessive moisture problems.
Check the manufacturer’s instructions for installation. They may require a concrete foundation or a concrete slab as a base. Make sure you are able to meet their requirements and provide the correct fall on the floor with adequate drainage.
If you are buying a kit, remember that it will be easier to install using two people. If you don’t have much experience with DIY then you may have to buy new tools or learn new skills to make the installation a success.
5. Check the reputation of the manufacturer. Any greenhouse you buy costs money and involves a lot of time and effort to erect and install. Do your homework beforehand and find out about the manufacturer and any bad reviews that may have. It is no use buying an expensive greenhouse only to find that the panels don’t fit together or that there is no proper after sales service. Read their website and do an internet search for reviews. Bear in mind that unhappy customers will always shout louder than happy ones so remember that the reviews may be unintentionally biased. Always read the fine print and ask yourself some basic questions:
Ask around at local gardening clubs or online gardening forums for information. Many people are very helpful and you may get offered many years’ experience with various types of greenhouse.
The popularity of greenhouse purchasing in your area will govern the number of dedicated greenhouse installation contractors available. If you haven’t many dedicated contractors in your area then you will have to consider choosing from contractors with related skills. The majority of contractors erecting and installing greenhouses will have a more general trade such as:
A lot of greenhouse manufacturers supply their own installers who arrive with the materials in prefabricated kit form and erect, install and fit accessories so you are given ownership at the end of the job with a fully working and tested greenhouse. The main advantage of using the manufacturer’s erectors is that they will have been trained on the installation of the greenhouse range. They will have all the required tools and will have access to the specialised instructions provided by the designers. Because the structure will be erected by the company, the company knows under what conditions the structure was assembled so the warrantee will be valid from the start.
Whichever contractor erects and assembles the greenhouse you will have to ensure that certain requirements are being met.
The cost of buying a greenhouse kit will vary depending on the size, materials and what accessories you choose. Obviously it will be cheaper to build the structure yourself but using a contractor will ensure the job is done quickly, professionally and with a warrantee. You will have to factor in the cost of excavation to provide a level area on which to build and the preparation and pouring of concrete foundations. Likewise the cost of installing electricity and plumbing will need to be considered. Larger structures may require permits which will cost extra. Considering an average sized greenhouse:
|Contractor installed||$14,000||Average size|
|DIY installation||$3,500||Average size|
|Basic beginner’s greenhouse||$250||6ft x 8ft hoop polytunnel|
|Experienced grower’s greenhouse||$3,000 to $7,000||For a 12ft x 12ft greenhouse|
|For commercial use||?13,000 to $30,000 (average cost is about $25 to $30 per square foot.||For a 500 to 1,000 sq. ft. These also have HVAC systems as well as automatic watering and extra grow lights. Flooring is permanent concrete with proper drainage.|
|Glass||$2.50 per square foot.||Minimum specification is double strength glass|
|Polyethylene||$0.15 per square foot.||Plastic film. Can be strengthened using a woven mesh. Very popular with hoop greenhouses.|
|Fibreglass||$75 per 6ft x 8ft panel|
|Polycarbonate||$55 per 8ft x 4ft sheet||Can be single skin, double or triple skin providing insulation from cold and protection from hot sun.|
|Cedar wood||$1 per linear foot||Insulating, beautiful, durable|
|Steel||$2.50 per linear foot||Strong, harder to work with.|
|Concrete||$10 per squarer foot||Requires nonslip texture and drainage.|
|Paving slabs||$8 to $12 per square foot|
|Gravel||$0.75 to $3 per square foot||Needs weed block fabric underneath.|
|HVAC & lighting||Over half of the total cost would cover this including installation by licenced contractors. On average over $8,000 on a $16,000 structure. Automatic systems are only necessary on larger structures. On smaller ones the gardener can do this manually|
|Grow lights||$30 to $150 each|
|HVAC systems||$100 up to many thousand dollars|
|Potting benches||$100||For 6ft long bench|
Today we have talked about the various types of greenhouse and associated structures that are available. In order to learn how to design and build a greenhouse for your own personal requirements we had to understand a little about the history and evolution of the greenhouse phenomenon. We discussed the materials that can be used and when to choose the different types of material. We talked about building your own from new materials as well as from upcycled alternatives and we also talked about buying a greenhouse kit or ready made structure from the various manufacturers available. To erect an average sized greenhouse is easy to do if you have basic DIY skills but for anything larger it is always worth employing a professional contractor or asking the manufacturer to supply their own installers.
With a greenhouse it is so easy to expand your ideas and experience of what gardening entails. As well as making it easier to grow plants that commonly occur in your area; you may be able to grow many new and exotic vegetables that were only a dream before buying or making your own greenhouse.
With the increasing occurrence of variable weather conditions, gardeners and growers worldwide are learning to take control and provide a stable and welcoming environment for their plants. They can achieve this partly by using greenhouses and partly by using other garden sheltering structures. Though the wind may blow, temperatures fluctuate and nights are chill, in the greenhouse all is calm, warm and constant and your plants will always flourish.