It may be easier to spread out the watering efforts during the first, most intensive phase after planting. You can plan to water some your plants each day rather than all of them, and cycle back around. You can also look at aids like Treegator watering bags for your larger plants (specifically the “donut” shaped style) which will let you fill up the bags all at once and provide a slow release of water for the plants over several hours. 

Always water directly at the base of your new plant – Their roots haven’t had time to spread out yet, so sprinklers and overhead watering often won’t get the water where your new plants need it. Watering at the base of the plant also prevents the foliage from staying damp, which can lead to health problems for many plants. A watering wand can make directed watering easier when you're doing it by hand. Low and slow watering helps, and if the water is running off over the mulch surface, it is not getting to your plant.

Your plants will need more care and water if they are planted during the hottest and driest months, and you may need to adjust your watering accordingly. Similarly, you'll need less supplemental water for trees and shrubs planted in cooler season, and fall into early winter is a great time of year to plant evergreens and any large plant material.