Allotment Greenhouse Guide

The features you have to look out for when choosing an allotment greenhouse do not differ a great deal from those when you are purchasing one for your own garden.

A bright interior, good ventilation, easy access are just a few considerations that are common to both situations but on an allotment there are a number of others, not least whether the local council or land owner will allow you to install a structure of any size.

You may well need special permission and this must obviously be obtained before going ahead with your purchase. However, when any formalities are sorted out, what type of greenhouse should you go for?

Different Types Of Allotment Greenhouse

Timber Or Aluminium

Many people would say that timber models have a more appealing natural appearance, they also absorb and retain heat better. However cost and practicality should also be considered, metal greenhouses are cheaper and as a general rule allow in more sunlight, they are also easier to assemble and move if for any reason you give up the allotment. As shown in this Halls Popular Green 6ft x 8ft Greenhouse.

Glazing

Whichever glazing you choose, Horticultural, Toughened or Polycarbonate, there are again advantages and disadvantages. They all offer good light transmission but, for safety reasons, it is best to avoid Horticultural glass, especially if you have children helping you on the allotment, as it breaks into dangerous shards.

Toughened glass is safer as it shatters into small pieces but, better still, Polycarbonate is twin walled and offers superior insulation, saving you money if the greenhouse is heated. Perhaps most importantly for an isolated allotment, these two types of glazing are less likely to suffer wind damage.

Size

A modestly sized greenhouse is all that you need for an allotment perhaps 8ft  x 6ft, you're not running a commercial operation and this will give you all the capacity required for sowing seed and potting on while growing indoor tomatoes and other crops that require just that little bit of extra warmth.

Optional Extras

Ventilation is very important in any greenhouse to regulate temperature especially if it is on an allotment some distance away and you might only visit the plot irregularly. In addition to a louvre vent to maximise ventilation, installing automatic vents would be a great idea, so that in hot weather your plants won't wilt.

For similar reasons in the height of summer, blinds or shading paint should be used to protect plants from scorching.

Most plants on your allotment will prefer rain to tap water so, if your greenhouse doesn't have gutters, fit them and channel the water via a rainwater collection kit into a butt and invest in a water can.

Finally, security must be an issue. There may be valuable items in the greenhouse and allotments tend not be well protected, so a lockable door might be a good idea. As shown in this Swallow Kingfisher ThermoWood Greenhouse.

The Best Location For A Greenhouse

Choose a position that isn't under trees or shaded and preferably not too close to a public footpath to avoid the threat of vandalism. The entrance should face away from the prevailing wind to lessen the chance of glazing being blown out and a nearby water tap would be useful.

For the base, slabs or treated fence posts or railway type sleepers on a bed of sand or gravel are preferable to large amounts of ecologically suspect concrete. With a spirit level, ensure that the foundations are perfectly horizontal. They must also be square and a little larger than the greenhouse's quoted dimensions as these might be approximated or lost in translation from imperial to metric.

Why Should I Get An Allotment?

You can grow a vast range of fruit and vegetable varieties, much more than is on offer in a supermarket and chosen for taste rather than their appearance or long shelf life. You know the growing conditions and, if you are organic, that no chemical sprays have been used or the apples haven’t been waxed.

And don't forget the health benefits, there's nothing more therapeutic, mentally and physically, than working the ground on a sunny day away from any domestic worries and stress.

There’s been a huge increase in the demand for allotments over the past few years. Although High Street shops and your local supermarket are convenient places to buy food, their shortcomings are many and various. There seems to be lots of choice, but is this really the case? When was the last time you saw Picasso or Pentland Javellin potatoes for sale ? Have you ever seen a named variety of carrot or beetroot displayed ?

Do you know anything about the strawberries you are buying except that they’ve probably been flown in from Israel ? There's nothing better than eating seasonal food, that how it's supposed to be consumed - asparagus from the Vale of Evesham in May not from Mexico in October.

Ok you might not have strawberries all the year round from an allotment but logic says that freshly picked produce is going to be more tasty than a product that has been transported around the world. And that’s even before looking at any ecological considerations.

Understandably production from an allotment decreases during the winter, although it is possible for all round growing, and of course parsnips and sprouts can come straight from the ground to your plate on Christmas Day.

But most vegetables can be frozen or stored, for example properly dried properly onions will last into the new year, and beetroot stored in damp sand will have the same longevity. If not quite as good as freshly dug out of the soil, stored vegetables and fruit still have many advantages over shop bought produce and there is nothing more satisfying than tasting the fruits of your labours.

How Can I Get An Allotment?

Most are owned by your local council and can be rented at a very low cost. Contact the council and find out who is responsible, due to their popularity you normally have to put your name on a waiting list.

You may be lucky to obtain an allotment straightaway but this might be on a site that is overgrown and hard to let. If you like a challenge that’s fair enough but it might also lack facilities or suffer from vandalism.

It’s more likely that you’ll have to wait a year or so, perhaps several, to get a good plot. During the last war there were 1.4 million allotments, today this figure is down to about 300,000 after thousands were sold off in the 1980s and 1990s due to a lack of demand. Ironically, some council waiting lists have now grown so large that they have been closed.

To speed up the process, contact the council regularly. Take a photograph of any sub-standard plots and email the appropriate council officer. Although councils have become increasingly keen to evict plot holders who have let their allotment go to waste, you can’t rely on their vigour in this matter. Allotments are loss makers for the council so they might not be top of their list of priorities. Persistence is the key.

There are also some sites on private land that you may enquire about and the National Trust launched an initiative some years ago, creating 1200 new plots in various locations.

If all else fails remember that due to the Small Holdings and Allotments Act of 1908, you can approach the council with five other council tax payers and request that they provide allotments. However, even if you gain a local authority’s interest, the process may be slow, as planning permission must be obtained for land that hasn’t been used previously for horticulture.

What Can I Grow On An Allotment?

You probably have some idea as to what to grow, obviously your favourite vegetables will top the list and you'll want to experiment with varieties that are difficult to obtain from the shops. 

As to what to grow and when, although it will certainly happen, plan not to grow more than you require, some produce will store well but others such as salad leaves deteriorate quickly and fresh is always best.

Sow in moderation over a period of weeks not all in one go. Grow 'expensive' vegetables - main crop potatoes, although tastier than those from the shops, might not be financially worth the effort. Experiment a little to find out what grows best, if anything doesn't do well it's not the end of the world.

Just by looking around at other plots will indicate what vegetables grow well but before attempting to grow anything you should get to know your soil and conditions.

The perfect plot where you will be able to grow the widest range of vegetables will have well drained soil, not too sandy or heavy, with a ph around 6.5 – 7. South facing, receiving all day sunshine unhindered by trees and overhanging branches would be good, and sheltered from the prevailing wind and with water taps within easy distance.

But perfection is hard to obtain, so first look at the site and assess the prospects. Your choice of vegetables, and how well they will grow, depends on certain criteria - some, but not all, of which can be manipulated. It may be possible to get rid of branches that shade the allotment, but not the trees. You can't alter which way the sun goes around but you can have a large influence on soil composition. You can't move the site down south if you are up north, but you can grow vegetables that are more in tune with that climate.

The soil's acidity or alkalinity can be adjusted to a certain extent by the application of lime for example to reduce acidity, while manure has the opposite effect. This needs to be done regularly as rainfall will naturally wash away whatever is applied. Manure or compost is generally applied in the autumn and as a spring mulch but lime will have most effect a few weeks before sowing.

Plan ahead properly, sketching out what goes where in the first and subsequent years. 

What Are The Different Types Of Soil?

There are five basic types of soil, they all have certain advantages when it comes to growing and they all present individual problems that demand particular management.

Clay

The main problem with clay is drainage, as a result it should be nutrient rich but hard to work. Dig over in the autumn, introducing organic matter, and let the weather do its work. Lime will improve drainage, but you must balance the amount you use with what you want to grow. If it’s very heavy, work in course grit, you can also use raise beds to help the soil both dry out and warm up.

Sand

Easy to work, but any nutrients are easily drained, so large amounts of organic matter can increase its water retentiveness and additional fertilizer can be used to replace nutrient deficiency. Try to mulch as much as you can and cover the soil with lots of vegetation all year round to minimize nutrient loss. If you are growing vegetables, sow green manure, when this is dug in it will add nutrients and improve the soil structure.

Silt

With a structure similar to clay, the biggest problem is drainage. It’s unwise to to walk on this type of earth when it is wet as you will only compact it even more. Dig it over in the autumn so that frost can help to break it down, introduce coarse grit and organic matter and use raised beds to warm up and dry out the soil.

Chalk

This, similar to sand, is a free draining soil from which nutrients can easily be leached. It’s also very alkaline. Digging in the autumn is not really necessary, leave that to the spring before you sow anything, and as there’s probably not a lot of top soil, don’t dig too deep. Add organic matter to increase acidity and aid drainage. Make sure that the ground has a good covering of vegetation throughout the year, including green manure in the winter and mulch with peat, grass cuttings and manure.

Peat

This type of soil has a tendency to be acid so use lime to balance the pH especially for vegetables and fruit. Peat is made up of decomposed vegetation so there is no need to dig or add any organic matter, but you may have to use an organic fertilizer to combat any nutrient deficiency.

How Can I Improve The Soil?

It is important that you understand the make-up and characteristics of your soil to put a strategy in place that will help to, if not guarantee, achieve maximum fertility and productivity. Soil matures over a number of years, don’t expect a quick fix. But there's no doubt that the addition of organic matter and fertilizers, used conjunction with good management, such as crop rotation, will increase your chances of success.

All soil will benefit from the addition of organic matter, it will help water and nutrient retention in sandy soils and drainage if your soil is heavier. The most widely used soil conditioners are compost and manure but alternatives include mushroom compost, wool shoddy, seaweed, composted pine bark, spent hops and peat.

What you use and how much will depend on your soil’s structure and the plants you wish to grow. For example mushroom compost is slightly alkaline so will be good for acid soil, pine bark has no nutrients so is best used as a mulch to retain moisture and increase acidity, while seaweed is particularly rich in trace elements.

Fertilizers will supplement manure and compost, ensuring that your soil contains the correct amount and proportion of major elements such as nitrogen, phosphorus and potassium together with trace elements that include iron, zinc and copper. Blood, fish and bone, hoof and horn, wood ash and rock potash are examples of organic fertilizers that will add these essential elements in different proportions to rectify any deficiencies in your soil.

Is Crop Rotation A Good Idea?

Grow the same vegetables in one bed every season and the specific nutrients that a particular crop thrives on will become exhausted. Pests and diseases such as club root will also be more likely. These problems will be prevented if you rotate the plots where you grow the three types of vegetable – brassicas, legumes and root - over a three year period.

There are exceptions such as rhubarb and asparagus which can have a permanent site. For the others, in the first year one plot can have brassicas including cabbages, sprouts and cauliflowers; another root vegetables such as potatoes, beetroot, parsnips plus onions, marrows, tomatoes; while growing on a third plot will be peas, beans, sweetcorn, spinach, lettuce.

Then in the second year, brassicas move to where the root vegetables were the year before and the root vegetables go to the plot formerly occupied by peas and beans, that have moved onto the old brassicas plot. And so on into the third and subsequent years.

By rotating the crop you will also save on resources, only for example spreading lime or manure where particular vegetables demand it.

What Are Raised Beds?

Boards, railway sleepers or something similar surround raised beds that are filled with top soil and organic matter to form a deep fertile environment of your own creation. Deep beds are similar but you dig down about a spade's depth, removing perennial weeds and fill with organic matter and soil. Don't make the beds too large as you should never walk on them compacting the soil. An excellent example would be the Forest Caledonian 6ft x 3ft Raised Bed.

These types of bed enable more vegetables to be grown at a greater concentration. There is less or no digging as there is little soil compaction and drainage is improved. Crops are within arm's reach and can be easily harvested. Weeds are also effectively dealt with, either eliminated or suppressed with a mulch. Bear in mind though that these beds are not suitable for certain crops such as runner beans and brussels sprouts.

What Are The Advantages Of A Raised Bed?

There are several reasons why raised beds have become extremely popular.

You can control in a much more effective way the soil’s pH. Most vegetables prefer neutral to acidic growing conditions. So if you have naturally alkaline soil, by raising the bed you can create a more acidic environment.

As the bed is deep and the soil not compacted, the roots have lots of room to grow downwards. Hence vegetables can been sown in blocks instead of rows and grown closer together, significantly increasing yield.

Easy access is also guaranteed since the bed is only 4ft across and can be tended from either side. As you don’t tread on a raised bed, the free draining soil structure should be maintained and only a little forking before planting is required.

As for maintenance, add a layer of compost or manure every spring and mulch to discourage weeds. A crop of green manure at the end of the season would be useful.

What Are The Disadvantages Of A Raised Bed?

There are only a few drawbacks. If you buy the boards, there is the initial expense and effort in creating the beds. You may need a friend to help with the work.

Since the soil should have good drainage, extra watering may be necessary especially for seedlings and young crops.

Not all vegetables can be successfully cultivated. For example, potatoes need earthing up and staking runner beans in soft soil isn’t satisfactory.

However, when all these factors are considered, raised beds certainly do make sense. Increased productivity will soon outweigh the initial expenditure and, unless you enjoy digging, they are very much a labour saving idea.

How Do I Build A Raised Bed?

To construct a raised bed, you’ll need two boards measuring about 1in x 4ins x 4ft long and two others of the same thickness and height but as long as you like, 6ft or 8ft would be a good choice.

Nail or screw 12in pegs near the end, and flush with the top, of each board. With the pegs facing inward, use a mallet to drive them into the ground, so the boards form a rectangle. A long spirit level is useful to ensure that they are level.

Now fill the bed with a mixture of well rotted manure, compost and top soil to create a fertile mix.

If you're unsure about constructing one yourself, several manufacturers have easy to assemble raised beds made from excellent quality timber, for example, this Zest Sleeper 6ft x 1ft Raised Bed.

What Is No Dig Growing?

It's just what it says, gardening that requires no digging which is the scourge of most vegetable growers, especially those with bad backs. It is based around not treading on and therefore compacting the soil, and spreading compost over the soil, then letting the worms do all the hard work for you.

If you are growing vegetables on an existing traditional bed, dig it over one last time and remove any perennial weeds. Then add a thick (3ins) layer of compost or organic matter or both. This needs to be repeated annually in the autumn, however if you have any surplus material you can add it throughout the year especially after harvesting early vegetables.

Over time you will find that there is less weeding because you are not disturbing the weed seeds, more worms hence better aerated soil and more nutrient rich casts, and a greater amount of mycorrhiza fungus that allow plant roots to absorb nutrients. Water retention will also improve, which will particularly help raised beds that are prone to drying out faster than open ground.