Answer: First of all, amending only the planting hole isn't really a good idea. The roots will tend to stay in the amended soil rather than spreading out into the poor, native soil. This can result in poor development later on and even girdling (strangulation) of the plants. A better idea is to amend a large area to encourage root growth out and away from the main stems of the plants.
Your plants should be at the same soil depth as they were growing in the nursery containers. So, dig a large enough hole that when you set the nursery pot in, the plant will be growing at the same level as it was in the pot. On a slope, this means the higher part of the slope is the growing level and the lower level should be extended out to form a watering basin. This water basin will erode over the first or second growing season, which is fine because it will have served its purpose. You'll want to water each plant deeply once (or twice) each week during the first growing season. Best wishes with your planting project!
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