Oak leaves are very acidic, between 4.5 and 4.8 on the PH scale. Furthermore, soil with a neutral PH is ideal for fruit plants. Therefore, oak leaves will not harm, making the soil entirely acidic. Just a little bit of the PH value can decrease. Oak leaves are beneficial for fruit trees because, in addition to their mulching benefits, they aid in maintaining the fruit trees' ideal, neutral PH. In contrast, apple trees and other complex woody plants benefit greatly from a mulch of oak leaves. And that's not the only benefit of using oak leaves as mulch around fruit trees. Mulch made from oak leaves doesn't decompose, so you can use it on any tree. Surprisingly, they were immune to forces that might otherwise alter the soil's composition. To that end, if you have a fruit tree and want to protect its trunk, it's not a terrible idea to use oak leaves as mulch from a distance of six inches.