Many methods of watering used by gardeners today are not environmentally responsible!Our purpose in watering plants is to do it correctly and not to waste water - especially during drought conditions.
Do not try to water by hand! It is time consuming and rarely puts down enough water to do the garden any good.
The proper watering technique simulates a gentle rain over a long period of time, putting down 1" - 1 1/2" each time you water. You should water for 8 - 12 hours every 10 days or only 3 times per month. Uncompacted clay soils cannot absorb more than 1/4" of water per hour.
You can measure your water output by placing 3 coffee cans, marked to a 1 1/2" level, in the area of your sprinkler. Place one close to the sprinkler, one in the mid-range of the sprinkler, and one at the farthest reaches of your sprinkler. Time how long it takes your cans to reach the 1 ½" mark, and that will become your watering time. If you are using the proper sprinkler head, this should take from 8 - 12 hours. We have found 2 ½" over a 24 hour period has worked the best.
You shouldn't worry about disease or mildew resulting from "watering from above" - "Mother Nature" always waters that way! In fact, research shows that this type of watering is less harmful than the dew that falls overnight and sits on the plants for long hours. It is also all right to water at night - Mother Nature does that a lot too!
How about the underground sprinkler systems?
They are wonderful! You don't have to drag a hose around, they can be set automatically or manually, and they save time. However, they usually don't meet the needs of the plants. You must set underground sprinklers properly to emit a gentle rainfall over a long period of time, and not more often than once per week during dry periods (best is every 10 days using 1 ½" of water). Recycle timers can be set to follow the above recommendations, for example set them for water on for 20 minutes, water off for 40 minutes, water on for 20 min, off for 40 min, etc., until you reach the desired amount.
Soaker hoses put out double or triple the water needed and can waste water, consider using recycle timers for these as well.
If you use above ground sprinklers, you should definitely try the ones that we use here at the Nursery. Our gardens are watered using a brass impulse head with a 9/64 nozzle for gentle watering. Our sprinklers are not adjustable. They only go in a complete circle. Andre gave me the following explanation for this:
Our sprinkler is designed with a small nozzle (9/64 opening) so that it puts down less water per hour than most other sprinklers. This means it waters more slowly and thus the water you do use on your lawn or garden has more time to seep into the ground and there is less likely to be water loss due to runoff. Many of the sprinklers on the market today are adjustable to water various parts of a full circle and rely on a kickback device to accomplish this. These sprinklers require a nozzle with a larger opening (thus more force) to trigger the kickback, and therefore put a lot more water down per hour and you usually get much more waste due to excessive runoff.
Andre’s sprinkler goes in a full circle and has a screw-in diffuser to adjust the distance of the water throw.