Do trees need fertilizer?
Usually not. An established tree, especially in a lawn that gets fertilized, does not need fertilizer unless a soil test or symptoms say so. Fertilize when a $15–$30 soil test shows a deficiency, growth is poor with no other cause, or the soil is compacted urban fill. Use slow-release nitrogen in early spring or fall; never feed a stressed tree.
Forest trees are never fertilized and grow for centuries. Yard trees get fertilized every year by people who mean well and companies that sell the service, and it rarely does anything for them. A tree is not a tomato: its roots cover a huge area, it recycles its own leaf litter, and its growth is limited by water, light, and root space far more often than by nitrogen. Fertilizer has a narrow place, and the starting point is a soil test, not a bag.
| Situation | Fertilize? | What to do instead or as well |
|---|---|---|
| Established tree in a fertilized lawn | No | It already gets lawn fertilizer through its roots |
| Established tree, healthy, normal growth | No | Mulch ring; water in drought |
| Newly planted tree, first year | No | Water about 10 gallons per inch of trunk per week; mulch |
| Tree under stress: drought, construction, storm damage, disease | No | Fix the stress first; fertilizer makes it worse |
| Thin leaves or dieback on one side or the top | No | That is roots, water, or disease; see an arborist |
| Soil test ($15–$30) shows low nitrogen or a specific deficiency | Yes, to correct what the test found | Slow-release nitrogen or the specific nutrient, at label rate |
| Small pale leaves and short twig growth across the whole canopy, no other cause | Yes, after a soil test | Slow-release nitrogen, early spring or fall |
| Tree in compacted urban soil, parking strip, or a container | Often yes | Slow-release nitrogen; relieve compaction; mulch |
| Yellow leaves with green veins (chlorosis) on oak, maple, or pin oak | Not standard fertilizer | Usually iron or manganese locked up by high soil pH; soil test, then a targeted treatment |
How do I know if my tree needs fertilizer?
Two pieces of evidence, together. The first is a soil test from your state cooperative extension lab, which costs $15–$30 and reports pH and nutrient levels for the root zone; pull samples from several spots under the canopy. The second is the tree itself. Fertilizer deficiency looks like a whole tree growing slowly: twig growth of only an inch or two a year on a young tree, leaves smaller and paler than the same species down the street, but even across the canopy. Trouble on one side, at the top, or on individual limbs is almost never a nutrient problem. That is roots, water, or one of the common tree diseases, and feeding it does nothing. A low test result plus uniform poor growth is a yes. Anything else is a no until you find the real cause.
What fertilizer is best for trees?
Slow-release nitrogen, granular, broadcast over the root zone. Nitrogen is the nutrient trees are most often short of and the one that leaches out of soil; phosphorus and potassium are usually plentiful and only worth adding if the soil test says so. Slow-release forms feed over months instead of forcing a flush of soft growth. Spread it evenly from a few feet out from the trunk to the drip line and beyond, since roots typically extend 1–3 times the canopy radius, at the rate on the label, and water it in. Fertilizer spikes concentrate everything in a few holes and feed a few roots. Deep-root injection by a service gets fertilizer under a lawn without burning the grass, but it is no better for the tree than granular and not worth doing without a test. What an arborist can and cannot do with soil treatments is on can an arborist save my tree?
When is the best time to fertilize trees?
Early spring, just before buds break, or fall after the leaves drop but before the ground freezes. In both cases the roots are active, the soil is moist, and the nutrients are in place for the next growth flush. Avoid summer: fertilizer then pushes growth into heat and drought and adds to the water demand. Avoid late summer through early fall on deciduous trees, because the soft new growth it produces does not harden before frost. Once a year is plenty. Water it in, and put the mulch ring back or top it up; mulch breaking down is the slow, steady feeding that forest trees live on.
Can fertilizer hurt a tree?
Yes, in several ways. A stressed tree, whether from drought, construction damage, storm loss, transplanting, or disease, does not have the root system to support new growth, and fertilizer forces it to try. The rule is fix the stress first: water it, mulch it, get the compaction or the pest dealt with, and give it a year. A newly planted tree is the same case and should not be fertilized in its first year; see how and when should I plant a tree? Too much nitrogen on a healthy tree produces long, weak shoots that attract aphids and scale and snap in ice storms. And lawn weed-and-feed products contain broadleaf herbicides that trees take up through roots under the lawn; a maple with curled, distorted leaves in late spring has often been dosed by the lawn treatment.
Does lawn fertilizer feed my trees?
Yes, and this is why most yard trees never need their own. Most tree roots live in the top 12–18 inches of soil, exactly where lawn fertilizer ends up, and they spread 1–3 times the canopy radius, so a mature tree's root zone covers most of a typical lawn. A tree standing in turf that gets fed three or four times a year is taking up far more nitrogen than any tree in the wild, If the lawn is fertilized, cross tree fertilizer off the list and spend the money on what the tree does lack: deep water in a drought and a mulch ring instead of grass at the base.
No independently confirmed professional review is on file yet.
Not yet independently reviewed. Figures are typical US ranges for planning purposes, not quotes.