Mature peach trees that are well established in the landscape or orchard require regular, but relatively light annual maintenance to ensure their health and fruiting vigor. According to the University of Georgia, mature trees are considered to be those peach trees that are fours years of age and older.
Ensure ample direct sunlight for your mature peach to keep it healthy and producing substantial fruit harvests. Prune away or remove any nearby trees to structures that may be shading your peach tree as shade will diminish fruiting. Ensure morning sun particularly, as dew needs to be evaporated off of the fruit or disease can result.
Water your mature peach tree deeply and regularly, applying a bare minimum of 36-inches of water over the course of a year. Increase the rate of irrigation in July and August, applying between 35 and 40 gallons of water per day, per tree.
Fertilize your mature peach trees twice each year, once in early March and again in early August. Apply a cup of 10-10-10 fertilizer for every year of the tree's age, up to a maximum of 10 cups per year, each spring. Apply a cup of calcium nitrate for every year of the tree's age, up to a maximum of 4 cups, each fall. Skip the calcium nitrate in years where the previous seasonal crop was lost to a late spring freeze. Apply according to label directions around the entire root zone of the tree but away from the trunk.
Prune your mature peach tree each year lightly to remove low, drooping branches and dead or damaged wood in the spring before new growth appears. Place cuts back to a point of healthy wood or down to the parent branch, just outside the slightly swollen branch collar. In July, prune out any vigorous, vertical shoots that are growing upright inside the canopy causing crowding or shade, but leave the smaller shoot less than 12-inches in place. Cut down clean with the parent branch.