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THE GREENHOUSE

 

SELECTING THE TYPE OF GREENHOUSE

The correct name for a greenhouse clad in glass is 'Glasshouse'. As this section includes greenhouses covered in other materials, the name greenhouse is more appropriate. The selection of a greenhouse can be based on many considerations. The available space will usually determine the size chosen. Most people would like the largest greenhouse they can fit in. However cost constraints and available free time are equally as important in considering the size .

Greenhouses can be quite cheap or very expensive. Weak flimsy frames, covered in polythene are the cheapest, and will be better than nothing. They don't last very long and aren't really suitable for heating. They are also prone to high levels of condensation and big temperature fluctuations. This type are really just polytunnels made in the shape of a greenhouse.

Where a really good greenhouse is wanted at the lowest possible price, the Aluminium frame glasshouses are the best choice. These types are better for plants too - by having a thin frame and more glass, they allow in maximum light. The main drawback is they are not particularly beautiful to look at, especially in an ornamental setting.

For a higher price and a better look, wooden frame glasshouses are a good choice. The emphasis is more on how nice they look, rather than what is best for light levels. The wooden frames are thick, and usually closely spaced. This looks highly ornamental but doesn't allow for best light levels within the house. However in Summer that is not such a bad thing. Wooden greenhouses will last a very long time, possibly a lifetime if well maintained.

Even more expensive, but very nice if you can afford it, is the cast iron framed greenhouse. Usually done in a retro styling from the Victorian age, and in many different designs that recreate those grand designs, but on a smaller scale.
The cast iron greenhouse could be considered a lifetime investment. People who move house several times in a lifetime should think twice before spending so much money. This is not the type of greenhouse which can be dismantled and moved.

 

 

 

SITE LOCATION AND POSITIONING OF THE GREENHOUSE

There may not be any choice where the greenhouse can go in a small garden. The most important things to consider are, how sheltered will the greenhouse be from strong winds? and how far away will it be from trees? Trees certainly must not overhang the greenhouse or block out light. Those are the two essential considerations.

Other things to consider is the convenience of using the greenhouse in relation to the rest of the garden. Whether a greenhouse runs North to South or East to West is hotly debated. The fact that people can't agree, must mean that it can't be obvious which is the right way, and therefore probably doesn't matter very much. Being close to a tap is important. Even if rainwater is gathered from the greenhouse roof into a water butt, in a dry Summer that butt could well be empty when needed.

Using rainwater in the greenhouse can be a way of introducing pests and diseases. People believe rainwater is best. This can't always be true. Rainwater can be high in toxins and even nowadays may be acidic. To keep a greenhouse as clean and sterile as possible, tap water is probably better. Use the rainwater on the garden plants instead. Research has proved that the temperature of the water doesn't make any difference to the plants (as long as it isn't hot water) even when the tap water is very cold. The practice of leaving a can of water sitting to reach room temperature isn't of any benefit.

It is helpful to be able to reach the greenhouse all the way round for cleaning etc. Even a path just one slab width, all the way around will be enough, Don't plant or cultivate right up to the greenhouse.

Apart from those gardeners fortunate enough to live in very quiet, or very select areas, a stone through the glass from time to time is quite likely if the greenhouse is positioned on the side of the garden adjoining a public footpath, or other public area, such as a park or recreation ground. Being next to a golf course is also a bit of a short straw, as flying golf balls and glass do not mix too well. It's surprising how many gardeners do not even think of these potential problems when deciding on the placement of the greenhouse.

 

 

INTERNAL LAYOUT OF THE GREENHOUSE

Few gardeners have room to waste in their greenhouses, so it is important to construct staging in such a way that 2 and maybe even 3 tiers of shelving can be accommodated. Plants requiring some shade can be placed on the lower benches and those requiring maximum light on the highest. The propagating area must be situated in a semi shaded part close to the source of power (usually electricity). Electricity in a greenhouse must be installed to conform with building regulations. These change from time to time so there is no use in going into them in this article in any detail. However it is for sure that electricity in a greenhouse must have it's own trip switch on the fuse box and be protected by a RCB, not just run from a plug socket in the house and across the garden ( that is only acceptable for short term electricity, such as mowing the lawn, and even then a removable RCB should be plugged in first to comply with the law) . There are also rules on how far a cable must be below ground or how high above ground level it should be. Fittings within the greenhouse should be of the industrial style grey box plug sockets with the rubber surrounds.

Air heating is usually either from bottled gas or Electrical Fan heaters. Neither is a cheap way to heat, especially with Electric fan heaters but usually the only option. If the heating can be incorporated into the household mains natural gas supply then the cost will be much lower, although more expensive to begin with due to the cost of installation. DIY on gas appliances is illegal. All work must be carried out by a registered gas installer.

Propagators are very efficient, and use little electricity. It can be far more economical to have more of these and a lower air temperature.

In a small greenhouse the best layout is a path down the middle, in line with the door and the benches positioned either side and at the top. Larger greenhouses can have a central bench as well as benches around the edge. The path then goes all the way around the central bench. Dividing the greenhouse into two, by using sliding doors, with a hot end and a cold end is a very good idea in large greenhouses. There is no sense in heating it all, when all the space isn't needed.

 

 

MAINTAINING A GREENHOUSE ENVIRONMENT

The greenhouse environment must be maintained to a standard that is best for the majority of plants within it. Some plants will never be totally happy in a mixed greenhouse, because of their special requirements. Such plants would ideally have a greenhouse to themselves with the growing conditions optimised. A good example is Cucumbers and Tomatoes. These cannot be grown in the same greenhouse and both given the ideal growing conditions. Either it will mean a compromise or complete failure of one or the other. People will keep on trying to grow the two together, but neither crop will give its best. Cucumbers require a very hot and humid atmosphere . Tomatoes require a dry and well ventilated atmosphere.

Most plants are happy somewhere in between, and where a mix of plants are kept in a greenhouse, then in between is the best way. A combination of lots of ventilation on fine sunny days as well as regular damping down of the floor will give a good mix of humidity and fresh air.

Auto vents are good for people who are away from home daytime. They aren't perfect, as auto vents don't take into account how windy it is outdoors, If the weather is hot and sunny, but at the same time blowing a gale, the vents will be open at a time when they should be shut. High winds in a greenhouse not only wreck the plants inside but could well damage the greenhouse itself. As most of us don't spend our entire life at home, the auto vents are still the best option.

When doors and vents are open, it is a good idea to secure some fine garden netting over the openings. It is very disheartening to come home and find the neighbours cat curled up on one of the trays of seedlings, or find that a bird has been having a dust bath in trays of sown compost. Very easy to not think about these things happening, but they so often do.

LIGHTING IN A GREENHOUSE

Lighting within a greenhouse can mean simply a light bulb somewhere to allow the gardener to see after nightfall, or it can mean artificial lighting in the form of Growlamps. These are very effective in extending the seasons and for growing plants out of season. The simplest way to do it is to use fleuresent strip lighting. These are not really very good unless there are lots of them placed close together.

Mercury bulbs are popular because they are cheaper to buy. They produce too much heat in a small area, in relation to the amount of light they produce (measured in lumens) so therefore are not very efficient in turning watts of electricity into light. However the light produced from mercury bulbs is high in blue light, which is the light that plants like best. Do not use mercury lighting in confined places, like closed propagating cupboards or boxes, or the plants will fry.

Far better, but far more expensive is the Metal Halide bulbs. These produce a lot of blue light, and come very close to natural daylight. They turn nearly all the electricity into light, with very little heat produced. Very high output of lumens per watt. They can't just be plugged into a socket, they have to be used with a special box that gives the bulb a peak or surge of electricity at start up time to kick the bulb into life.

Bearing in mind that these grow lamp bulbs are sold in wattages between 125watt and 500watt ( only 400w to 500w is adequate ) and for that amount of electricity they light a miserly 1 sq metre or so, they are only for people who do not mind huge electricity bills with little in return. It is quite easy to manage without them in an amateur setting. They are used extensively commercially for inducing out of season flowering, and for winter crops, where light levels in December and January are too poor for acceptable growth.

 

 

AUTUMN AND WINTER MAINTENANCE

Fair weather gardeners will be planning on putting the greenhouse to rest for the Winter from about October time. Others will be thinking about clearing Summer grown crops, such as Tomatoes and putting the greenhouse to good use by bring in outdoor grown plants like pot grown late Chrysanthemums.

Between clearing the Summer crops and either shutting up the greenhouse for the Winter or bringing in plants from outdoors it is a good idea to do some maintenance while the greenhouse isn't too full.

Brush down the frame and glass to remove spider webs etc, then give the frame and glass a good wash and scrub. Some household detergent in the water will not harm plants. Wooden frames may need painting or varnishing. Iron framed may need just painting. Aluminium doesn't need any maintenance other than washing.

The benches can be washed and scrubbed and disinfected. Staging topped with gravel can be levelled and then sterilized with Jeyes Fluid or similar. A good way to get the hard to reach areas clean and free from pests and diseases is to use an Insecticide smoke. These look rather like fireworks and are ignited in the same way. Close up the greenhouse as tightly as possible. Place the smoke somewhere central. Light the wick and then run, closing the door behind. The greenhouse will fill with smoke and kill off any bugs and insects and eggs of larvae etc. Do not go back in to collect your hat that you accidentally left behind, or for any other reason. Leave for a day then open the door first, followed by the vents. By this time it is safe to enter, even though the smell will linger for several days.

Other maintenance to consider, is the annual servicing of gas appliances (only by a professional) used within the greenhouse and checking that all electrical equipment and fitting are safe. Check condition of cables and plugs. If the greenhouse is not used over winter remove and store the appliances somewhere dry and safe.

The greenhouse can now be fully stocked again with plants brought in from outdoors or closed up for the winter.

 

 

SEASONAL USES FOR GREENHOUSES

There are 4 seasons and a use for the greenhouse during all of them. Without some heat there isn't much that can be done in winter however. Spring may be regarded as the main propagating period. Full use should be made of propagators and soil warming cables to raise plants from seeds and cuttings.

Remember when sowing that a tray of seeds takes up very little room, but once those resulting seedlings are pricked out or potted, then the greenhouse will soon fill up. By sowing later (late March instead of late February) the risk of heavy frosts will have passed. Greater use can then be made of cold frames to raise the plants. Plants grown cold will be slow and maybe slightly unhealthy to begin with, but they will make the best plants in the end.

The higher heat levels in the greenhouse can be reserved for the fussier and more tender plants. By summer, bedding annuals raised from seed and vegetables started in the greenhouse will be out in the garden. Certain pot plants like Fuchsia and Geranium will be happier displayed and grown outdoors with some dappled shade.

The high Summer temperatures of a greenhouse are better suited to a range of foliage houseplants of tropical origin, and growing plants that would not produce a good crop outdoors. Tomatoes, Cucumbers and Melons are examples.

Many plants are grown outdoors during Summer in large pots and brought into the greenhouse in Autumn for flowering and over wintering. Examples of these are late Chrysanthemums, Carnations, Fuchsia, Geranium, Regal Pelagoniums. Cuttings can be taken in September of Fuchsias and Geraniums if the plants have enough non flowering growth. The cuttings must be kept cool, and Spring is a better time to do it, even though many people favour Autumn.

With enough heat, a lot can be done in Winter. Growers of show vegetables and flowers never have a break. The seeds and cuttings are started during Winter to produce the larger plants. Winter flowering pot plants like Cyclamen, Cineraria and Solanum will keep a greenhouse full of interest during the dark months too. Artificial lighting is needed to accompany high temperatures, if drawn thin plants are to be avoided.

 

 

SOWING AND PROPAGATING WITHIN A GREENHOUSE

It is a good idea to have a separate potting shed or some other suitable area with a bench, away from the greenhouse. Trying to do the sowing and pricking out, and cuttings in the greenhouse will mean a lack of elbow room, as well as compost and plant material dropped about the greenhouse.

Once sown and covered, or cutting inserted, carry the trays or pots to the greenhouse, then water them, then place them in the propagator. Depending on the requirements, either cover to exclude light, or just lightly shade those seeds requiring light to germinate.

Cuttings need warm bottoms to encourage rooting, but cool tops to prevent rapid transpiration through the foliage. A plant without roots cannot afford to loose water from its leaves. It can't take anymore up, until rooting takes place. Keep the cuttings misted to help prevent further loss of water.

When growth starts again on the cuttings, it is safe to assume the cuttings have rooted. Those cutting that do not begin growth and instead shrivel up are the ones that have failed to root. Discard them once it is obvious they have failed. With the correct conditions a 100% take is quite possible with many of the easier plants like Fuchsia.

When seeds germinate move the tray from the bottom heat straight away, and place on the staging in full light. As soon as the seedlings are large enough to handle they can be pricked out. Take them back to the potting shed to do this. Don't let the seedlings get too large, especially if they have not been sown as thinly as they ought to have been. The seed leaves should be fully developed, but the true leaves only just starting to show.

As Winter turns to Spring and then late Spring move more and more out of the greenhouse into Cold frames, or even just open standing out grounds, if the plants are hardy, or risk of frost has past.

Refer to the Crop guides for individual sowing and growing advice.

 

 

 

SUMMER MANAGEMENT OF A GREENHOUSE

In winter we are trying to keep as much precious heat in, whereas in summer we have to keep as much out as possible. Small glasshouses, and even worse polythene greenhouses, will suddenly rise in temperature, just by the sun coming out for a few minutes. Temperatures in small glass houses will go as high as 120 degrees C in a UK summer and in Polythene greenhouses as high as 140 degrees C. However much water is splashed about the temperature is hardly cooled at all, and the humidity becomes unbearable, both for people and most plants.

Without turning the greenhouse into a wind tunnel, opening doors at each end, if the greenhouse has doors at each end, will allow through ventilation. Slow fans of the type that move large amounts of air by having large slow propellers, rather than small fast ones are well worth installing. They look like canisters hanging from the eaves. Used a lot commercially, they are just as suitable in amateur settings.

A whitewash of thinned white matt emulsion is a cheap and easy way to shade greenhouses. Matt paint gradually comes off as the summer progresses and is conveniently all gone by Autumn. Don't use Silk emulsion or Gloss as it will not come off. Other similar brand name products are available which achieve the same thing. Fine mesh netting is another good way to shade a greenhouse. Bamboo blinds which let half the light through, are also a very attractive, and effective way of shading.

Keep the greenhouse clean and swept throughout the summer months. Damp down regularly, and wash paths and under the benches with a disinfectant solution, to maintain good hygiene. Take holidays in the winter, rather than rely on a neighbour to water the greenhouse while away for a week or two. The chances are they will be half hearted about it, and the contents of the greenhouse will suffer, or in the worst cases shrivel up.

When looking after a greenhouse, there is no better way, than doing the job yourself. A greenhouse is really a personal place. There isn’t often much harmony when two or more people get involved with one greenhouse. It is therefore essential that a gardener with a greenhouse is truly dedicated to it, and prepared to never be too far away from it in the Summer months.