Allotment Greenhouse Guide

To make your allotment as productive as possible, growing a wide variety of fruit and vegetables, as well as extending the growing season, many people consider installing a greenhouse on their plot. Read our guide for tips and tricks on the perfect greenhouse for your allotment.

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?

The Types of Allotment Greenhouses

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.

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.

Positioning

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.

How To Get An Allotment

Most are owned by the council and can be rented at very low cost. Contact the council and 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 perhaps several, to get a good plot. Thousands were sold off in the 1980s and 1990s due to a lack of demand but now some council waiting lists have grown so large that they have been closed.

To speed up the process, contact the council regularly. Councils have become increasingly keen to evict plot holders who neglect their allotment, so take a photograph of any sub-standard plots and email them. Persistence will pay off in the end.

There are also some sites on private land and the National Trust launched an initiative some years ago, creating a 1000 new plots in 40 locations, and 200 more have recently been made available.

As a last resort and if all else fails, under 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.

The Perfect Allotment

Perfection would be a south facing plot that receives all day sunshine unhindered by trees and overhanging branches. Sheltered from the prevailing winds and with water taps within easy distance. Well drained soil, not too sandy or heavy, with a ph around 6.5 - 7.

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.

First of all, analyse the soil. You can buy a ph tester kit to get an idea of the acidity / alkalinity or send the soil for a professional analysis to discover the exact make-up. Just by looking around at other plots will indicate what types of plant grow well.

Judging by what you find, and whether it is a heavy or light soil, incorporate soil conditioners to improve the structure. Most soils will benefit from lots of organic matter, it will help water and nutrient retention in sandy soils and drainage in heavier earth. As required, work in conditioners such as animal manure (invaluable but make sure it is well rotted), mushroom compost (slightly alkaline for acid soils), seaweed (rich in trace elements), spent hops (good conditioner with a few nutrients) or many others.

Raised Beds

Raised beds enable more vegetables to be grown at a greater concentration. Boards, railway sleepers or something similar can be used to create the that can then be filled with top soil and organic matter to form a deep fertile environment.

There is little soil compaction and hence no need for digging as crops are within arm's reach and can be easily harvested. Weeds are also effectively dealt with, either eliminated or suppressed with a mulch. However, bear in mind though that these beds are not suitable for certain crops such as runner beans and brussels sprouts.

What To Grow

You probably have some idea as to what to grow, obviously your favourite vegetables will probably 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 fast maturing crops at intervals to ensure a continuous supply.

Grow a good variety in moderation, so that you have rocket, spinach and lettuce for your sandwiches rather than a glut of one filling. Grow 'expensive' veg - economically main crop potatoes might not be 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.

Crop Rotation

Whatever you plan it is best to rotate the crops. Grow the same veg in one bed every season and the particular nutrients that crop thrives on will become exhausted. Pests and diseases such as club root will also be more likely. By rotating the crop over three plots you will also save on resources, only for example spreading lime or manure where particular vegetables demand it.

With the exception of a permanent site for crops such as rhubarb or asparagus, a three year rotation pattern should be sufficient. 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 and the root vegetables go to the plot formerly occupied by peas and beans, that have moved onto the old brassica plot. And so on into the third and subsequent years.