While automatic sprinkler systems are the most effective way of watering a lawn, drip irrigation, some drawbacks notwithstanding, is the preferred method for the rest of the garden plants. The essential difference between the two is that sprinklers throw water indiscriminately over the area they cover, as opposed to drippers that emit water in designated spots. Judging by the fact that sprinklers are still widely used for watering flowerbeds, trees and shrubs, it seems that the advantages of drip irrigation are not sufficiently clear to many gardeners. Before dealing with these, let's outline first the disadvantages involved with drippers.
*Installing a drip irrigation system is more expensive than a sprinkler system in terms of materials and labor. Furthermore, the life span of the dripper lines is limited to about 10 - 15 years - sometimes a lot less if periodic flushing is not carried out. While it's necessary to replace the actual sprinkler heads now and again, the underground piping ought to last well beyond a lifetime.
*The sight of irrigation pipes strewn on the ground is neither pleasing nor aesthetic. In addition, dripper lines are often damaged by birds or rodents, and periodic maintenance of the system is more demanding than for sprinklers. These last problems can be overcome however, by spreading an organic mulch over the pipes.
Despite the drawbacks, the overall advantages gained by using drippers are overwhelming, especially in the matter of water conservation. In fact the use of drip irrigation is vital if the term "water conservation" is to be upgraded from a slogan to a reality. Assuming that the system is installed and operated correctly, how can it save water in comparison to watering with sprinklers?
*Sprinkling water on the bare earth between the shrubs and trees causes a good deal of run-off, meaning that a considerable proportion of the water emitted cannot be taken up by the plants. This problem is particularly acute on slopes and gradients. Drip irrigation on the other hand, emits water at a rate at which it can be absorbed by the soil.
When it comes to trees and shrubs, there is no need in any case for water to cover the entire area. Drippers spaced at constant intervals, say 0.5 m × 1.0 m (1.5 ft × 3 ft) that is 0.5 m between the drippers, and 1.0 m between the lines, will supply water evenly and sufficiently for the roots to take up. Furthermore, shrubs and bushes prevent some of the water from reaching the ground, while drippers ensure that all the water applied, percolates down to the root zone.
*Sprinkling on bare earth, rather like heavy rainfall, causes mechanical damage to the structure of the topsoil. Organic mulch solves this problem of course, but at the expense of wasting water, because the mulch layer itself absorbs much of the water that is emitted. With drippers however, all the benefits of mulch are attained without a similar waste of water.
Although water conservation is the primary reason for adopting drip irrigation, the method has other important benefits.
*The rate of weed germination is significantly reduced as dry areas are interspersed between the moist ones.
*The majority of pest and disease organisms thrive in humid, warm conditions. Sprinkling on warm evenings for example, means that the air around the plants' foliage is saturated with moisture until the early morning sun, reduces the humidity somewhat. This is great for fungi such as powdery mildew, but disastrous for many garden plants, especially for rose bushes. Watering by means of drippers does not seriously raise the humidity in the crucial vicinity of the plants' foliage.
Conversely, it is sometimes argued that a splash of water on the leaves is beneficial for washing off dust, and for reducing infestations of organisms like spider mites, that prefer dry conditions. All this is true but does not justify the use of sprinklers, as the occasional use of the garden hose, (carried out in the early morning!) is usually enough for these purposes.
