Taken from Eclectic Gardener @ www.teachinggarden.org
Written by Alan Hickman

I don’t remember when we last had a good soaking rain that put any significant moisture into the soil, and, as I write, the prospect for precipitation is no better than "chance of showers." Perhaps this is a good time to review watering, watering equipment and the use thereof.
Watering is not a one-size-fits-all operation. Established trees seldom need help finding adequate moisture. Most established perennials can go for weeks without rain and even some annuals - once they have their roots down - can get by for at least a week or two without additional water.
Even moisture-loving plants can be kept happy with a little forethought and planning. The three ferns which do best in my garden are planted beside the steps in to the house. When I make the dogs’ supper, I empty their water dish over one of the plants; the ground stays moist and I don’t waste water.
The condition of the soil and the amount of cover the soil has are critical factors affecting moisture retention and plant welfare. With Brampton’s clay soils, the addition of copious amounts of coarse sand is fundamental to creating a loam suitable for growing flowers or vegetables. If the soil shrinks and cracks when it dries, then there is not nearly enough sand in the mix. You can add peat moss ‘til you go bankrupt and it will still do nothing to create a good loam. The incorporation of organic material merely masks temporally the basic deficiency in the soil structure.
Except in a desert, nature will not allow the surface of the soil to remain bare - at least not for long. In the woods the soil is covered with a deep layer of litter and, on treeless land, every square centimeter supports some sort of grass or forb.
On the forest floor, dry upper layers of leaves and twigs prevent evaporation of soil moisture while the moist under layers provide habitat for all manner of organisms which aerate and add organic matter to the mineral soil. On prairies and in meadows, the close-packed plant stalks and leaves shade the surface and reduce wind speeds at soil level to practically zero. Moisture loss is minimal and trapped bits of plant debris from past years create an humid blanket and a food source for soil organisms.
In horticulture, bare soil is a recipe for accelerated water loss and for weeds. Cultivated areas need to be mulched with three or four inches of fluffy, easily broken down, organic material to replicate natural conditions. Shredded leaves and bits of grass and twigs from last year are an obvious component of any garden mulch. For the rest, use whatever you can get your hands on cheap - preferably for nothing - and in quantity.
The heavier the soil, the more critical it becomes to conserve such moisture as there is. At Peel Teaching Garden, where there is no protection from day-long sun and where the wind is unbroken, soil that has been kept under a foot or two of straw since the winter, is moist, workable and ready for seeding. In other parts of the garden, a pick would bounce rather than penetrate the surface.
Eventually, if a drought lasts long enough, every garden needs to be watered and - if those I see while driving around town are any indication - many people haven’t got a clue how to do it.
The object of the exercise is to get moisture into the ground to where a plant’s roots can use it. Watering the air and spraying foliage is just a waste of water, time and money. If you have a thick layer of mulch, the best and quickest way to water is with an open hose. Set the faucet to give a rapid flow of water - but not a soil excavating jet - and, keeping the end of the hose about six inches above the ground, go around each perennial plant a couple of times. In five or ten seconds each plant will get its nominal inch of water and then the hose can move to the next specimen. The mulch layer will serve to distribute the water around the plant as well as to protect the soil surface from erosion.
In a larger garden, the black, porous, soaker hoses are invaluable. Because each perennial needs a loop of hose around it, 50' of soaker won’t go nearly as far as you think it will, so be prepared to get a lot more. Also you can’t join endless soakers together in a long string. Domestic water pressures and flow rates are too low to get significant water at the far end of a long leaky line. From experience, two 50' soakers fed from a ‘Y’ in the middle is about all an outside tap can supply.
Although soakers deliver water quite slowly over a long length, if the soil is very clayey and dry, they can still cause puddling and wasteful run-off. If you are not going to be around while the system is running, an automatic metering device can be purchased for a reasonable price.
As a starting point, a meter could be set to run for five minutes and turn off for five - to allow the water to soak into the ground - and to cycle like that. After say three hours, set the timer to shut the water off. The total amount of water delivered can be measured by putting a margarine tub under the soaker. Adjust the setup to run until an inch of water has dripped into the container and that will be enough for at least a week.