Greenhouse Gardening

by frankbeswick

A greenhouse, sometimes known as a glasshouse, is an excellent addition to any garden that enables you to widen the range of vegetables and fruit that you grow.

Widening the range of crops that you grow and the time when you can work is important to gardeners,especially in damp and wet climates like the one that I live in,so a greenhouse is a very useful and enjoyable addition to a garden. Greenhouses come in a variety of shapes and sizes, and are composed of differing materials. But they can often be a gardener's delight and a place where many happy hours can be spent, in most kinds of weather, though in extreme conditions you may need to be in a safer place.

The image above shows a small growhouse that I keep for propagating seedlings.
Photo by Frank Beswick

A little private space

I  had plans for today, but I didn't ask Mother Nature, whose intentions were somewhat different from mine. And she timed it well.  I reached the allotment at 13:45 set to plant up a whole bed of leeks. Then it began to pour with rain. At first a few drops that might have been a passing shower, but it went on for the rest of the afternoon. It's annoying, for we have just had the two best days of the year, rich sunlight, warm temperatures, then rain again. But it mattered little, as I simply went into the greenhouse, a small structure eight feet long and six feet wide, to spend an hour or so doing jobs. As it is six feet high at the ridge it can easily accommodate my five feet seven and a half, so it is a comfortable  place to work.  

Last year a colleague and I were clearing a plot after its tenant left, when Jeff spotted an abandoned grapevine in a pot, which he gave to me. I had never grown grapes before, so I wondered how to best cultivate it. The greenhouse was the obvious choice, so I gave the grape a pot of its own and placed it in a corner. Over the year it grew, but fruited not,however grapes take time. I did not over-fertilize or over-water, as grapes can cope with drier conditions. But a few weeks ago I spotted buds! The grape was thriving, and it was also trailing, so I rigged up a few loops of string to fasten it to the frame. But today, I spotted them,  tiny little clusters of fruit, baby grapes. Now for the next step. A bit of research is  going to be needed, for I know that the grape must be pruned, some clusters must go to enable the favoured ones to mature, otherwise they will be small and sour.    

But the first job was watering. You must ensure that the plants are well-watered. Tomatoes in particular can suffer from blossom end rot if they are inadequately watered. This is a condition in which the base of some tomatoes has a dry scar-like area replacing the red, moist flesh. There are no fruits yet, but I am taking no chances. I did not apply tomato feed today, as I applied it yesterday, and once a week is enough. But I am going to get some liquid seaweed for the plants, all of them, not just the tomatoes. It is a great fertilizer. 

I also trimmed some of the lower shoots of the tomatoes, as you need to control the green growth, as excessive greenery lessens the amount of fruit on the plant. The day's jobs in the greenhouse were completed by some weeding and tidying, as I had been a bit untidy in allowing spare pots to pile up on the floor, so they were tucked away in corners, awaiting someone who wants to give them a good home. Why weed the greenhouse? Not all my floor is paved, and besides the flagstone path I have covered the ground with wood chip,and so some weeds sneak in.Weeds versus humans, an unending battle!


Inside the Greenhouse

A view into the greenhouse
A view into the greenhouse

In the greenhouse

The tiny cluster to the right is a bunch of grapes
The beginning of a bunch of grapes
The beginning of a bunch of grapes
Frank Beswick

Variety in Greenhouses

Greenhouses come in a variety of shapes and materials. The broad divide is between greenhouses and polytunnels, which you can see in the advertisement above. Polytunnels tend to be made of polythene, and they need to be properly erected, as any spot where the polythene flaps will soon tear in a strong wind, though a well-erected polytunnel can stand strong winds. They are usually pinned to the ground by their frame and have their sides dug into a trench which is then filled in. However, the polythene will decay in sunlight after a few years and so the fabric will need regular replacement. There are cheaper tunnels suitable only as temporary structures for the summer season, but in Winter they must be taken down to prevent them from blowing way.

The greenhouse will have a frame of wood or metal, and aluminum is popular, as it is light and relatively inexpensive.Some houses are made of cedar and are considered classy structures for wealthy gardeners. Mine is aluminum! The sides can be either glass or polyurethane. I use a mixture. Glass is better  for preserving heat, and I inherited glass when I purchased my greenhouse second hand, but it frightens me. Glass when it breaks makes for a savage cut, and I have grandchildren, so I must think of their safety when they come to the allotment. Polyurethane is hard to break, making it far safer than glass is

But whatever you do the greenhouse should be protected from wind, and as regular readers know wind for me on my plot is allotment enemy number one. The house should  be laid on a base of either concrete or paving stones, I have paving stones laid around the base of the walls. Before the glass is in place you need to drill into the stones and bolt the structure to them, all around the walls. But to reinforce the structure I used a very powerful cement that I squeezed from tubes into the gap between the stones and the frame, and I used plenty of it. So far the structure has held. But I am not complacent. When the Autumn/Fall comes I will check the nuts to ensure that none have worked loose and will ensure that the W clips that hold the windows in place are still fully holding.

But critical to wind protection is to position the greenhouse correctly. I had to ensure that as the prevailing winds come across my allotment from the West, the door was not facing west, so my door faces south. Otherwise, if wind gets in it has to get out, and it can exit taking windows with it. This happened once to me on a previous plot, and the greenhouse went bang,sending one shattered pane twenty two feet. That was a lesson learned.  


Heat,Air and Pests.

At times when the sun is not shining heat is needed, especially in a place like Britain where there can be frosts until the end of May. Tomatoes and some other plants die in frost, so at times a heat source is needed. I used to use a paraffin heater, but it was unreliable and sooty, so now I use candles, which take the chill off the air on colder nights. Were I in North Britain I would definitely get a heater, though, but North West England is not too bad for cold, it is just windy and damp.

But saving heat should not make you oblivious to air circulation. If the air is allowed to go stale and still around plants, especially in damp conditions, fungal diseases can set in. Botrytis is a horrid one that requires destruction, and the same goes for members of the mildew family. Remember also, that as tomatoes belong to the same  family as potatoes they are susceptible to potato blight, which likes damp conditions and still air. Once blighted, the tomato will have to be destroyed. So ensure that the house is ventilated properly. Leaving the door open for a short period everyday will work wonders for ventilation, especially in a breezy area such as mine.

Cleanliness is vital for the destruction of pests and diseases. Once a year after Summer is over and the plants are finished, the greenhouse needs to be thoroughly cleaned. Wash the windows and if there is any algae growing there, spray it. I like to use sprays containing pelargonic acid, which is biodegradable. It is lethal to weeds, but take precautions for your eyes and keep away from children. The cleaning should involve all pots and crannies being washed out with detergent to ensure that any pests or their eggs are not overwintering. This is important, as there are some greenhouse pests that can survive winter in the snug warmth of the greenhouse, and eggs certainly do. 



While for many growers the greenhouse is where the  crops are grown to harvest, there are many who have a house for propagation of plants that will be replanted outdoors. If you look at the thumbnail sketch at the top of the page you will see that I have a small growhouse where seedlings are propagated, some of which you see in the picture below, which shows Broccoli seedlings.

To propagate you must be organized. Remember, you will be growing from seed, which is what I have not been doing in my greenhouse. I keep that for the growhouse in the back yard shown above. To grow from seed you can use seed compost, which gives you the best results, but you can use general purpose compost, which has worked well for my seeds.Seed compost is not very nutritious, as seeds do not need a high level of soil nutrient, as they begin to grow from their own internal resources.

You need benches to take the small pots in  which you plant your seeds. You also need a variety of pot sizes so that you can pot on when the seedlings outgrow their pots. You will need potting compost. Potting compost follows on from seed compost, and it is of a higher nutrient level, as the seedlings are taking nourishment from the soil when they are potted. But it is not over-rich, as some composts might be too rich for some seedlings.

Technology is needed. I visited an allotment site recently as part of my duties as vice-chair of my allotment society and was impressed by the array of greenhouses in which they grow products for sale. Each had its own heater powered by mains electric.But you can use a simpler heating  system. Some growers irrigate their  greenhouse crops with a variety of irrigation systems. One is  a trickle hose that operates at mains pressure but has little holes along the sides to allow water to trickle out into the beds. Others use drip irrigation systems from above. As for me, I use a watering can! I still obtain a good range of produce from my structure despite the lack of technological sophistication. I like to use technology, but I am not a fan of it for its own sake, and if I can get away with low tech I am content.

As you are growing in containers you will need to ensure that the soil quality and water remain suitable.Containers dry out quicker than the ground does, so it is vital to attend to the watering.Soil in containers wears out, so it needs to be refreshed. I renew mine each Spring, but I feed it during the year, sometimes with liquid tomato feed, other times with liquid seaweed, and also  with pelleted chicken manure, a small handful of which will well nourish a pot of  vegetables.


Seedlings being propagated
Seedlings being propagated
Frank Beswick

Another Greenhouse

I have been busy preparing the ground for a new structure. Two good friends,a husband and wife couple,  are leaving the allotment, sadly, and rather than sell their greenhouse to a new tenant, they are giving it to me. I will need to lay a base of paving stones, and then the whole structure will be unbolted and shifted on strong poles carried by four men to be laid on my plot. I have made the pathway clear for it. Then it will be bolted down and secured with pink grip.

What to grow? This will be where I start propagation in earnest. So far propagating from seed has been a minor part of my gardening.Hopefully next year things this deficiency will be put right.

Updated: 05/12/2016, frankbeswick
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frankbeswick on 06/18/2016

My greenhouse is a basic design and my allotment site has only just acquired electricity, so I do not use supplemental lighting. I grow at the moment: tomatoes, an eggplant, peppers, a grape vine and courgettes. I am getting another greenhouse when a friend moves on to another allotment, but that will not have supplemental lighting.

DerdriuMarriner on 06/18/2016

frankbeswick, Thank you! Do you just not grow in your greenhouse the plants that have a need for some periods of darkness or for supplemental lighting?

frankbeswick on 05/13/2016

Thanks for this observation. We dwell in very different areas, and yours is far warmer than mine, so your experience will complement my experience. Just to show my situation: tonight 13th May, I am going to have to take anti-frost precautions in the greenhouse after a chilly weather forecast! Heating will have to be used.

You are right. A greenhouse can become too hot, and that's why we need to carefully control the heat,water and air flow.

Pollination can be a problem. That's why I have never grown sweet corn in the greenhouse, as it is wind pollinated and so I cannot rely on the breeze necessary to move the male pollen. A shame really, as sweet corn is always a bit of a challenge where I live, due to our being near its maximum latitude. Keeping a door open in hot,lightly windy weather when bees are operative helps pollination. Large commercial growers often keep bees in each of their greenhouses. I have many bumble bees near my plot, and they are the best pollinators, far better than honey bees

blackspanielgallery on 05/12/2016

My concern has been with pollination, since bees cannot easily access the plants.
Greenhouses reflect infrared rays, which is why they keep heat in. In this area we can actually get a greenhouse too hot.

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