Will placing citrus peel or citrus tea (orange or lime) on an anthill repel or kill the ants or other insects? Citrus peels are thought to contain a substance that is fatal to insects (d-Limonene).
When planting a new tree or shrub replace the soil in the planting hole with organic material such as compost. Everyone knows that plants love "organic stuff" and will grow rapidly.
The result in that the organic material will actually hinder further root growth long term. Moisture is another issue, it will actually wick away from the organic material back into the native soil and thus deprive the roots of the moisture newly planted trees and shrubs need. Use the native soil removed when digging the planting hole to backfill after planting. Your trees and shrubs will do much better.