How to Fertilize Trees: What to Use, When to Apply, and When to Skip It

Most established trees in residential yards don’t need fertilizer. That’s the honest answer nobody selling you bags of 10-10-10 wants you to hear. A healthy shade tree with access to decent soil, natural leaf litter, and occasional mulch already gets what it needs. I’ve got a 40-year-old Valley Oak in my backyard that’s never been fertilized once, and it throws shade across half the yard every summer.

But some trees do need help. Young trees still establishing roots. Trees in compacted clay or stripped topsoil from recent construction. Ornamentals that aren’t pushing the growth or flowers you expect. Evergreens that have gone pale. For those trees, the right fertilizer at the right time makes a real difference. Here’s how to do it without wasting money or burning roots.

Does your tree actually need fertilizer?

Before you buy anything, look at your tree. Healthy trees tell you they’re healthy.

Skip the fertilizer if:

• New twig growth is 6 inches or more per year
• Leaves are full-sized and dark green (or appropriate color for the species)
• The canopy is dense and even
• The tree is mature and established (10+ years in the ground)

Fertilize if you see:

• Pale, undersized leaves, especially on a species that should have dark green foliage
• Less than 2 inches of new twig growth per year on a tree that should be growing 6 to 12 inches
• Sparse canopy with thin branching when neighboring trees of the same species are full
• Soil disturbed by construction, which strips away topsoil and the organic matter trees depend on
• A young tree (under 5 years old) that has stalled after initial planting

Oregon State Extension notes that established trees growing near regularly fertilized lawns often don’t need supplemental feeding. The lawn fertilizer runoff is already reaching their roots. Double-dosing with a tree-specific application on top of lawn feeding can push excessive growth and create more problems than it solves.

What NPK ratio to use for shade and ornamental trees

NPK stands for nitrogen (N), phosphorus (P), and potassium (K). The three numbers on every fertilizer bag tell you the percentage of each by weight. A bag labeled 12-4-8 contains 12% nitrogen, 4% phosphorus, and 8% potassium.

Shade trees and ornamental trees need a different ratio than fruit trees. Where fruit trees want balanced formulas (1-1-1 or 1-2-1) to drive fruit production, shade and ornamental trees need nitrogen-heavy blends to support canopy growth and overall vigor.

The recommended ratio for shade and ornamental trees is 3-1-1 or 3-1-2. Clemson Extension and Oregon State Extension both confirm this. In practice, that means products like:

• 12-4-4
• 12-4-8
• 16-4-8
• 20-5-10

These deliver three to four times more nitrogen than phosphorus, which is what a shade tree’s canopy growth actually demands.

For newly planted trees, Penn State Extension recommends a more balanced formula like 5-10-10 for the first year, since young trees need phosphorus to build roots before they need nitrogen for canopy growth. After the first year, switch to the standard 3-1-1 shade tree ratio.

For fruit trees, the ratios are completely different. Our guide to fertilizing fruit trees in February covers the species-specific NPK requirements. Using high-nitrogen shade tree fertilizer on an apple tree is the number one reason homeowners get gorgeous foliage and zero fruit.

How much fertilizer to apply

University extension services agree on the math: base your application rate on trunk diameter, not tree height or canopy size.

The formula: 1/4 to 1/2 pound of actual nitrogen per inch of trunk diameter. Measure the trunk 4 feet above ground level (called DBH, diameter at breast height).

Here’s how that works in practice. Say you have a 10-inch diameter maple and you’re using 12-4-8 fertilizer:

• At 1/3 pound nitrogen per inch: 10 inches x 0.33 = 3.3 pounds of actual nitrogen needed
• The bag is 12% nitrogen, so: 3.3 / 0.12 = 27.5 pounds of product

That’s a lot of fertilizer for one tree. Which is another reason most homeowners should default to a lighter hand. For trees under 6 inches in diameter, use half the rate (1/8 to 1/4 pound nitrogen per inch).

The simpler approach: If you don’t want to do the math, UC Davis recommends 10-10-10 at 1 pound per 100 square feet of root zone area. Calculate the area under your canopy, buy the right amount, and spread it evenly. This is less precise but works fine for most residential situations.

Maximum amounts: Cap any single application at 6 pounds of actual nitrogen per tree, regardless of trunk size. More than that risks root burn and nitrogen runoff into storm drains.

Where to apply it

This is where most homeowners get it wrong. They dump fertilizer right next to the trunk and call it done. The feeder roots that absorb nutrients aren’t next to the trunk. They’re out at the drip line and beyond.

Apply fertilizer in a ring starting 2 feet from the trunk, extending out to at least the drip line. UC Davis research shows tree roots actually spread 1.5 times the canopy diameter, so extending your application beyond the drip line is even better.

Use a broadcast spreader for large trees. For smaller trees, hand-broadcasting works fine. After spreading, water thoroughly. A 30-minute soak with a garden hose or sprinkler washes the granules into the soil where roots can access them. Surface fertilizer that sits on top of the grass does nothing useful.

Never pile fertilizer against the trunk. Concentrated nutrients against bark tissue can cause chemical burns and invite disease.

When to fertilize trees

Late winter to early spring (February through March) is the best time for most shade and ornamental trees. The tree is still dormant or just breaking dormancy, and the fertilizer has weeks to dissolve and reach the root zone before active growth begins. Root systems start absorbing nutrients when soil temperature hits 40 degrees F, which happens in Northern California by mid-February most years.

Fall (late October through November) is the second-best window. A fall application feeds the root system during its fall growth phase and stores nutrients for the spring flush. Some arborists prefer fall fertilization because roots are actively growing while the canopy is shutting down, so nutrients go to root development rather than leaf growth.

Avoid fertilizing in summer and late fall. Summer heat stresses trees, and fertilizer stimulates growth the tree doesn’t need to be making when it’s conserving water. Late fertilizing (after mid-November) can push tender new growth that gets killed by frost. I learned this lesson with a young crepe myrtle. Fed it in October, it pushed a flush of soft new shoots, and a December freeze burned every one of them.

Frequency: Most shade trees need fertilizing once a year at most. Young trees in poor soil might benefit from twice annually (spring and fall). Established trees in decent soil might not need it at all. If you’ve been fertilizing annually and the tree looks great, try skipping a year. If it still looks great, your tree was telling you it didn’t need the help.

Shade tree species: what they actually need

Oak

Mature oaks rarely need fertilizer. Their massive root systems mine nutrients from a wide area, and natural leaf litter provides a slow-release nutrient cycle. The exception is oaks in compacted urban soil or near construction. If your oak is declining, get a certified arborist assessment before throwing fertilizer at the problem. Oak decline is more often caused by root damage, soil compaction, or disease than nutrient deficiency.

If fertilization is warranted, use a 12-4-8 or similar ratio at the lighter end of the dosage range (1/4 pound nitrogen per inch of trunk diameter). Oaks are adapted to lean soil. Over-fertilizing them promotes the kind of fast, soft growth that’s susceptible to pests and disease.

Maple

Maples are moderate feeders that respond well to spring fertilization, especially in their first 10 years. A balanced 10-10-10 or nitrogen-forward 12-4-8 in late February or early March supports the leaf canopy that makes maples worth planting. Sugar Maples and Red Maples in Northern California’s alkaline clay soil sometimes develop chlorosis (yellowing leaves with green veins), which signals iron deficiency rather than a lack of NPK. Treat chlorosis with chelated iron, not more fertilizer. For specifics on maple health and common issues, our types of maple trees guide covers species differences.

Dogwood and Redbud

Understory flowering trees like Dogwood (Cornus florida) and Eastern Redbud (Cercis canadensis) are light feeders adapted to the forest floor. A single spring application of balanced 10-10-10 at half the standard rate is plenty. These trees evolved in nutrient-poor leaf litter, and heavy fertilization pushes vegetative growth at the expense of the flowers that make them worth growing. If you planted them for spring blooms, go easy on the nitrogen.

Crepe Myrtle

Crepe Myrtles (Lagerstroemia indica) are moderate feeders that bloom on new wood. A spring application of 12-4-8 fertilizer supports the vigorous new growth that produces summer flowers. Apply in March when new leaves emerge. Don’t fertilize after June, or you’ll push late-season growth that delays flower bud formation and is vulnerable to fall frost. If your crepe myrtle blooms poorly despite good sun, the issue is more likely improper pruning than nutrition.

Evergreen trees: fertilizer needs by type

Evergreens have different nutritional needs than deciduous trees because they retain their foliage year-round.

Pine, Spruce, and Fir

Most needle evergreens are adapted to nutrient-poor soils. In a residential yard with decent topsoil, mature pines and spruces rarely need fertilizer. Overfertilization actually makes pines more susceptible to bark beetles by stimulating soft new growth that beetles prefer.

If a young pine or spruce is growing slowly, a light spring application of 12-4-8 at half the standard rate is enough. Apply it in April, after the last frost but before new candle growth starts.

Arborvitae and Cedar

Arborvitae and Cedar (Thuja and Cedrus species) benefit from annual spring fertilization more than most evergreens. They’re often planted as hedges or screens where dense, uniform growth is the goal. Use a 10-10-10 or evergreen-specific fertilizer in early spring. The nitrogen supports the tight, layered growth that makes arborvitae work as privacy screening. Green Giant Arborvitae in particular responds well to spring feeding during its first five years of establishment.

Holly and Broadleaf Evergreens

Broadleaf evergreens like Holly, Laurel, and Photinia prefer a slightly acidic soil. If your soil pH is above 7.0 (common in Northern California), standard fertilizer may be less effective because alkaline conditions lock out iron and manganese. Use an acid-forming fertilizer or add sulfur to lower pH. A soil test tells you where you stand.

Organic vs. synthetic: which is better?

Both deliver nutrients. The difference is speed and what happens to your soil long-term.

Synthetic granular fertilizer (the bags at the hardware store) delivers nutrients fast. Trees can access them within days of watering in. A 10-pound bag of 10-10-10 runs $12 to $20. The downside: synthetic fertilizer feeds the tree but ignores the soil biology. Over time, soil that gets only synthetic inputs loses organic matter, microbial activity, and structure.

Organic fertilizer (composted manure, bone meal, fish emulsion, cottonseed meal) releases nutrients slowly over weeks to months as soil microbes break it down. It feeds the fungal networks, earthworms, and bacteria that make soil healthy. The downside: slower results and higher cost per unit of nutrient.

My approach: Compost first, supplement second. I spread 2 to 3 inches of composted material under my trees every spring, from 12 inches off the trunk to the drip line. That handles the baseline nutrition for established trees. For young trees or trees that need a boost, I add a handful of granular 12-4-8 on top of the compost and water everything in. Total cost for five trees: about $30 to $50 per year.

A 40-pound bag of composted steer manure costs $5 to $7 at any garden center. Arborist wood chips (which decompose into excellent soil amendment) are free from most tree service companies. Combine the two and you’re feeding both your trees and the soil they live in.

Soil testing: the $25 shortcut

A $15 to $30 soil test through your county cooperative extension office tells you exactly what your soil has and what it lacks. I wasted years and hundreds of dollars applying balanced fertilizer to soil that already had plenty of potassium and phosphorus. The only thing my Sacramento Valley clay soil was low on was nitrogen and organic matter.

How to sample: Pull soil from 6 to 8 inches deep at four or five spots under your tree’s canopy. Mix them into one composite sample. Send it to your county extension lab or the UC Davis Analytical Lab. Results come back with specific recommendations for your soil type.

Test every 3 to 4 years. Soil chemistry changes slowly, so annual testing is overkill. But one test pays for itself immediately by preventing you from buying products your soil doesn’t need.

Common fertilizer mistakes

Fertilizing a tree that doesn’t need it. This is the most expensive mistake because it costs money and can actually harm the tree. Excess nitrogen pushes soft, fast growth that’s vulnerable to pests, disease, and frost damage. If your tree looks healthy, leave it alone.

Using the wrong NPK ratio. Shade tree fertilizer on a fruit tree gives you all leaves and no fruit. Fruit tree fertilizer on a shade tree shortchanges the nitrogen that drives canopy development. Match the ratio to the tree’s purpose.

Applying at the wrong time. Late-season fertilizing (July onward) pushes tender growth into frost season. Summer fertilizing stresses heat-tired trees. Stick to late winter or early spring for most species.

Dumping fertilizer at the trunk. The absorptive roots are at the drip line, not at the base. Trunk-dumped fertilizer burns bark and misses the roots it’s supposed to feed.

Ignoring the math. A bag of fertilizer with application instructions printed on the back is not a suggestion. More is not better. Overfertilization burns roots, contaminates groundwater, and promotes the kind of weak growth that breaks in storms.

Skipping the soil test. You wouldn’t take medicine without knowing what’s wrong with you. Your tree shouldn’t either. A $25 soil test prevents hundreds in wasted product and potential damage.

Fertilizer spikes, liquid feed, or granular?

Granular fertilizer (broadcast) is what Clemson Extension recommends for most residential trees. Spread it with a drop spreader or by hand across the entire root zone. It’s the cheapest option and distributes nutrients evenly. This is what I use.

Fertilizer spikes are convenient but concentrate nutrients in small pockets around each spike. Roots near the spike get too much, roots between spikes get nothing. They also cost significantly more per unit of nutrient. Skip them.

Liquid fertilizer (mixed with water and applied with a hose-end sprayer) works for quick fixes but doesn’t last. Nutrients leach through the soil faster than roots can absorb them, especially in sandy soil. Better for container plants than landscape trees.

Deep-root injection is a professional service where an arborist injects liquid fertilizer directly into the root zone under pressure. It costs $100 to $300 per tree but delivers nutrients exactly where they’re needed. Worth it for high-value trees with specific deficiency problems identified by soil testing.

When to call a professional

If a tree is declining and you can’t figure out why, stop guessing with fertilizer and call an ISA Certified Arborist. A professional can diagnose whether the problem is nutritional, structural, pest-related, or disease-related. Throwing fertilizer at a tree with root rot or borers doesn’t help and can make things worse.

An arborist consultation runs $150 to $350. That’s cheaper than a year of wrong fertilizer applications, and you’ll get an actual diagnosis instead of guesswork. Verify credentials at treesaregood.org. For tips on choosing a qualified tree care service, take the time to check credentials and insurance.

The bottom line

Healthy established trees in decent soil usually don’t need fertilizer. Young trees, stressed trees, and trees in poor soil benefit from a spring application of nitrogen-forward fertilizer (3-1-1 or 3-1-2 ratio for shade trees) spread from the trunk outward to the drip line. A soil test tells you exactly what’s needed so you’re not guessing. And compost, applied 2 to 3 inches deep every spring, is the best long-term investment you can make in your soil.

For fruit tree fertilization, which follows completely different rules, see our February fruit tree feeding guide. If you have fig trees, our fig tree fertilizer guide covers their unique low-nitrogen needs. Palm trees are another special case entirely, with potassium-heavy formulas covered in our palm tree fertilizer guide. And for the full spring maintenance routine that includes fertilizing, mulching, pruning, and inspection, our spring tree care checklist ties it all together.