Irrigation is the process of supplying water to dry land. It is one of the oldest and most important agricultural techniques, allowing farmers to grow crops on land that would normally be unproductive.
In a residential context irrigation is only necessary for aesthetic purposes, although those wanting to grow their own vegetables would obviously struggle if the soil was too dry.
Depending on the soil type and drainage, some sort of irrigation system may be required for an attractive and manageable garden to be maintained.
Things have advanced massively since the days of deliberate flooding. Simple canals and computer regulated machinery can now be used to carefully regulate soil saturation to the optimal level, with minimal water wastage. Such methods are usually confined to large agricultural developments, but scaled down versions are available to horticulturists.
Installation of such systems is most commonly a professional task, below are detailed the different types of irrigation system available and conditions which dictate their use.
Soil Types
Infiltration, the rate at which water passes through the ground is mainly dictated by soil type. Plant cover and soil saturation also play a small part, but these are both directly affected by the irrigation system anyway and so need not be considered. The main categories of soil are as follows:
- Gravel- This soil type holds very little water owing to the large gaps between stones with water moving over 20 millimetres per hour.
- Sand and Silt – These soils have a medium to high infiltration rate, meaning they hold water for only a short time. Loam (a combination of sand, silt and clay) unsurprisingly in the middle.
- Clay – This is the most compact soil type found in the UK and has a very low infiltration rate. In the summer months it can contract in the heat, causing large cracks to appear, even if the ground has a decent covering of turf. These large cracks increase the infiltration rate massively, but the water moves well beyond the root level of most small plants and grasses and so will not help the turf itself.
As a general rule, small amounts of water should be applied at regular intervals to most types of soil. This means that water is not wasted on sandy soils, as large volumes would pass through the soil straight away, and provides a chance for the water to soak through more clay based soils to prevent them from becoming waterlogged.
In addition to irrigation there are two other techniques for treating very impervious soils such as clay. A roller with spikes that remove small cores of soil from the ground which allow roots more room to grow and facilitate water movement down through the soil.
Another method is to add a chemical surfactant to the water which lowers the surface tension of the water, which again allows it to move through the ground more easily. Both these techniques can be used in conjunction with other irrigation systems.
How to prepare for the installation of irrigation services
Garden landscaping
- It's fair to say that the installation of an irrigation system can involve a fair amount of work. This can be minimised with careful planning and foresight. If the property is to be built on a new plot and the garden to be landscaped onto bare ground, almost any of the systems detailed can be used (depending on which is the most suitable).
- If the area that is to be irrigated has already been deliberately landscaped with fences and plants in place, the options are slightly more limited as these can obstruct pipes and turf may need to be taken up. If a pipe-based drip system is to be used it is most convenient for it to be installed before the turf is laid to minimise work.
- Ideally this should be done when there is no risk of a frost. If this can not be avoided, the area should be drained down after the installation and then irrigation begun fully in the spring.
Garden design and plant layout
- Before the system is installed, the garden should be split up into irrigation zones. These are sections of land which have different irrigation requirements, which will of course depend on drainage, soil type, aspect, plant type and cover.
- The requirements of each area can then be catered to with either a different level of water, administered through the same system; or covered by a separate system altogether. Computerised synchronisation of each of the irrigation components may seem somewhat overzealous, but this can be done relatively cheaply considering the likely price of the entire project, and is easily made up be using water more efficiently. If the zones were not dictated by plant type, then the garden should be planted with these zones in mind.
- Plants can easily be damaged by over watering, and so the water requirements and tolerance to drought and flooding should be similar for all the plants in each zone. Careful consideration of the water requirements will also help to save water and energy. In conclusion, the system should be installed with the zones in mind, but this of course requires the garden to be completed. If working from scratch, it is worth designing the garden and irrigation system alongside each other.
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Choosing a system
Drip Irrigation
This is traditionally the application of a constant steady flow of water to soil at low pressure. A series of tubes is placed either just above the soil surface, preferably below the leaf canopy of any plants, or in the soil itself at or above root level. Water loss is minimised through these measures as there is very little splash owing to the low pressure and short distance to the ground.
Reduced splash increases the amount of water which reaches the desired area of soil and means there is less opportunity for evaporation to take place directly into the air.
The purpose of the leaf canopy is to capture as much light as possible while minimising the amount of rain or moisture which is directed horizontally away from the plant roots. It is best therefore in terms of water conservation to set any irrigation system below this level.
Burying the drip system is reduces water loss even further by preventing run off across the surface, which can occur at very high rates on dry impervious ground. It also reduces the chance of damaging the system while weeding. The soil surface is also kept dry which can reduce invasion by weeds.
Some chemical insecticides and fertilisers are most efficiently applied via a drip irrigation system in terms of timing and precision of amounts to be used. This can lead to significant savings in money and maintenance time of the garden, care must be taken to ensure that the product is suitable for this type of application and will not damage the irrigation system.
There are many different manufacturers of the system components each with a vast range of products. One of the main factors that varies between systems is the emission device. This is point where water is released and can affect the amount of water released and the flow rate.
A good company will explain the differences between the products and help you to choose the most suitable.
It is very important that the correct sized valves, emission devices and diaphragms are used for the system to be efficient.
Hydraulic calculations must be made to make these decisions so you should ask the company to show you their workings even though you are unlikely to understand them. If the person you are dealing with looks completely flummoxed, it could be a sign that they are not as qualified as they’d had you believe.
To maximise the effectiveness of a drip irrigation system, it should be fully automated and connected to a series of sensors, the installation of these is discussed below.
There are several disadvantages and potential problems with a drip irrigation system. Costs of the product and its installation can be relatively high compared to more simple alternatives, although these may eventually be outweighed by savings in water bills.
The systems are vulnerable to blockage by organic matter, either in the water supply or algal growth in the pipes themselves. Chemicals and filtering systems can be used to minimise these problems. These problems should be brought up when considering drip irrigation and discussed with the installation company to fully assess suitability of such a system
Sprinklers
Sprinklers can be used to set up a simple irrigation system, and would normally be used with a simple tap timer. Sprinklers can be moved manually to ensure an even distribution of water over the ground, but a series of small fixed sprinklers are what is more commonly used in an irrigation system.
The “throw” of a sprinkler is the area of land which receives water from it and sprinklers are placed “head to head” meaning that they are placed sufficiently close together that there are not gaps of dry land between them.
This can mean that the sprinklers must either be large in size or number and so may not be suitable for irrigating some areas.
The garden’s function should be of primer consideration when deciding whether a sprinkler system is suitable. Pop up sprinklers are the best suited for lawns as they are out of sight most of the time. Most systems are fitted with internal filters to prevent them from being blocked by hard water. Before you purchase your sprinklers make sure this is the case.
Sprinkler systems must be completely drained before the winter to prevent damage, and some part may even need to be removed. A sprinkler system may last over fifteen years although they require regular servicing and replacement of parts.
Pumps
Small porous pipe dripper and microspray systems can be run simply from a tap. As the water is required to travel further however, the pressure required must be generated by a pump. Pumps of different sizes and strengths are available according to the type and size of the irrigation system. If the system is classed as a “permanently installed underground system” then bylaws state that it must be fed by a tank and pump.
This requires for a tank to be purchased and installed which may complicate planning stages and increase price. You should consider this excess price with the total price in mind and if it seems particularly high, discuss alternative options with the installers.
Always ask the company who is selling and installing the pump to explain processes such as “pump cycling” which can often reduce the efficiency of an irrigation system but can easily be solved with small adjustments.
Timers and sensors
Electronic timers and sensors which adjust the watering cycle according to rainfall, sunlight and soil saturation can be installed. This reduces water loss while ensuring plants receive water at the right time. The most simple system is a battery operated timer that will simply turn a tap supply on or off which supplies water to the whole area.
More complex computer driven systems may take information from across the system and adjust water pressure and output according to the requirements of each zone. Before purchasing such a system make sure that you will be able to fully operate the computers, as even the most self-sufficient systems need fine tuning.
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Choosing a Company
You should aim to find a company that is large enough to take on the work easily, but small enough that there is still a guarantee of a decent and personal service. An important factor is the timescale in which the job can be completed and whether you are insured if the work runs past the agreed date. This is particularly important if other landscaping work depends on the irrigation system being in place and functional.
A site visit should take place before quotes are obtained and detailed planning is carried out. A rough estimate of costs could be made from plans and photographs. You should always looks for a Water Industry Approved installer and ask for references and examples of previous projects.
More modern and advanced companies use computer programs to design and plan the systems, you should still expect a good level of human input and understanding however. Enquire about other professional qualifications regarding garden landscaping and design, although these are less relevant if the company is simply installing the system.
There is a great range of products available each with their own merits and drawbacks, having been designed with a certain type of system in mind. A reputable company will be able to explain these and help you choose. You should be wary of a company that tries to push you into purchasing a particular range as they may be working on commission and so will not have your best interests at heart.
Also make sure that the equipment you purchase and the installation is fully guaranteed and that they are prepared to carry out the required servicing on the system.