Generally, mature trees do not like to be disturbed around their root systems. White ash (Fraxinus americana and its cultivars) is more tolerant though.

Rather than chemical fertilizer, organic fertilizers such as compost are a better bet for your plants.There are several reasons to use organic rather than chemical fertilizer:

• Chemical fertilizer salts can build up and inhibit the tree's ability to take up micronutrients from the soil. Because the nutrients in chemical fertilizers are more readily available than in organic fertilizers, it's very easy to overfertilize and cause this damage.
• Chemical fertilizers primarily contain nitrogen, phosphorous and potassium, but not other macronutrients or the micronutrients and microbes that plants also need.
• Chemical fertilizers can reduce the activity of beneficial organisms that kill pest insects, decrease the spread of disease, and help plants gather nutrients and water.
• The ingredients in these fertilizers stimulate plant growth but don't promote life or soil health. They don’t replace the many trace elements that are gradually depleted by repeated plantings. Organic fertilizers, on the other hand, break down over time, improving the structure of the soil and increasing its ability to hold water and nutrients.

For information on types of organic fertilizers and their use, see Cornell University's Using Organic Matter in the Garden.

For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service