Deep watering that is infrequent saturates the entire root zone and minimizes the total loss of water due to evaporation. By watering only about once a week even as the surface area dries moisture is still available more deeply, where roots will grow in search of available moisture. By watering infrequently, roots are encouraged to grow down to find water.
The most critical phase of a plant or tree survival is when it is becoming established. Getting sufficient water to the roots is critical. Having a way to deliver that water slowly enough to soak deeply into the soil is essential. Using the right drip irrigation method is a great way to assure that happens, no matter where your plants are located. Another issue is growth ring for roots... they tend to match the diameter/perimeter of the limbs and trees above so if you water, try to water just outside the perimeter of the tree growth area to encourage the tree to extend its roots wider away from the center of the trunk.
Methods of Irrigation
Manual - Bucket/Spray, gutter redirects and sprinklers:
These are the most common and any DIYer can use various forms of water collection systems to aid in their efforts to collect and sometimes redirect water around the yard or into containers or planters. Manual is slow and not very convenient unless you borrow your kid's John Deere Jeep and have them lug around the water from plant to plant... hoping they don't run over your newly planted Black Eyed Susans.
Buckets and Garbage Cans:
Some people trap water in large 50-gallon rain barrels or another tip is to use a 30-gallon plastic trash can or barrel drill a few small drainage holes, fill with water and let the water slowly drain out - this of course is a bit unsightly, unless you like a black, 30-gallon trash barrel near your Weeping Willow Tree... some folks use the inexpensive 5-gallon paint buckets with small holes drilled in or with drip/soaker hoses jury-rigged to the bottom to allow for slow drainage. It is possible to camouflage or hide your large rain bucket within wooden boxes or fences - be sure to use a screen to keep out mosquitoes.
Automated irrigation systems:
These are fantastic but are difficult to DIY, can get pretty fancy and quite costly. Some cities are planning to add surcharges to homeowners that use these systems or have them installed in new/existing homes. Sprinklers are great, direct or indirect misting and can easily be placed anywhere you want to target spots that need attention. Downside with sprinklers can be wastage and evaporation - there's nothing quite like watering your sidewalk or driveway.
For beds and containers, the best way to keep plants hydrated right at the root zone is with drip irrigation. The water is delivered through a supply line that typically is flexible: plastic tubing. Along the supply line small holes are punctured into it where needed, allowing water to drip out at those points. Flexible tubing can also be tapped into the line, directing water precisely to the base of any plants or containers. The rate at which water drips from the end of the tubing is controlled by a plastic tip called an emitter. They come in different sizes depending on your desired flow rate. Drip irrigation kits and supplies can be purchased at garden centers and home improvement stores. They're easy to install. Add an automatic timer and you'll have a worry-free way to water effectively... Some downsides include clogged drip connectors, costly, works best for small individual plants and can get cumbersome running various lengths of hose that you have to hide or bury.
Portable drip irrigation in a bag:
There comes a point where it becomes impractical to extend a drip irrigation line too far into your yard or to a remote setting of your landscape. That can create a problem, forcing you to consider ever more efficient ways to water trees and shrubs. Treegator is a product that addresses that very issue. It's essentially a portable drip irrigation system in a bag. The "bag" is a leak-proof bladder that has tiny pinholes in the bottom. Wrap the Treegator around the trunk, fill it with water and, during the next six to 12 hours water is released slowly into the soil.
There are currently two models. One is a cone-shaped style that holds 20 gallons of water. The second has a lower profile and holds 14 gallons. They are an ideal solution for watering trees and shrubs in a way that allows the water to slowly soak the area around the roots. More information and ordering information is available at www.treegator.com. Downsides include, odd green pyramid on every tree in your yard, can be a bit costly.