Does my tree need fertilizer, and how should I fertilize it?

Many homeowners fertilize trees out of habit, but most established landscape trees don't need it — and over-fertilizing can do real harm. The key is to fertilize based on need, not routine.

Most trees don't need fertilizer when:

• They're growing in a lawn or bed that already gets fertilized
• They show normal annual growth and healthy green leaves
• They're mature and well-established

Signs a tree might benefit:

• Pale or yellowing leaves (with normal veins greener — possible nutrient deficiency or high-pH chlorosis)
• Very short annual twig growth compared to past years
• Recent transplant in poor or disturbed soil
• A soil test showing a genuine deficiency — this is the only way to know for sure

How to fertilize correctly (if needed):

1. Test the soil first. It tells you what (if anything) is actually lacking and your soil pH. Yellowing is often a pH/iron issue that nitrogen won't fix.
2. Use a slow-release formulation; apply in fall (after growth stops) or early spring.
3. Spread evenly over the root zone out to the dripline, not in a pile at the trunk.
4. Don't over-apply nitrogen — it forces soft growth that attracts aphids and is prone to disease, and it can pollute waterways.

Often more helpful than fertilizer: a proper mulch ring (see mulch question) and correct watering, which fix the issues people mistake for "needs feeding."