How to Fertilize Arborvitae Trees | Feed For Deeper Green

Fertilizing arborvitae isn’t complicated, but getting the timing and placement wrong can burn feeder roots or push tender growth that winter kills. The goal is one solid feeding in early spring that fuels the growing season without stimulating late-season flushes. Here’s the exact method that works, plus the mistakes that send trees into decline.

When To Fertilize Arborvitae

The best time is early spring, just before or as new growth begins. UConn’s extension service recommends fertilizing in early spring after a soil test, while Epic Gardening and Gardening Know How both point to the same window: spring before and during new growth. The season closes at the summer solstice — Gardening Know How advises stopping around June 20–22, depending on the year.

That cutoff matters. Late-summer or fall feeding triggers new growth that won’t harden off before frost, leaving the tree vulnerable to winter burn. Arborvitae in regularly fertilized lawns may not need any additional feeding at all, since they already draw on lawn fertilizer; amendment is only helpful where the soil test shows a need.

Which Fertilizer To Use On Arborvitae

Look for a slow-release, high-nitrogen formulation. UConn names 20-15-15 or 10-5-5 as solid choices; 20-20-20 and 10-10-10 also work well. The higher first number feeds the foliage that gives arborvitae their dense, green look. Slow-release granular forms are ideal because they meter nutrients out over months rather than dumping everything at once — a key difference since arborvitae feed steadily through the season.

If you’re choosing between products, see which slow-release fertilizers tested best for arborvitae before you buy. Whatever product you pick, follow its label instructions for exact rates and timing — the numbers below are the general extension-service guideline, not a substitute for the label.

How To Apply Fertilizer The Right Way

Application is straightforward but precise. UConn’s preferred method is to spread fertilizer on the soil surface over the entire root system rather than concentrating it in one spot, which reduces the risk of concentrated zones damaging tender feeder roots. The extension service’s rate is 1 pound of fertilizer per 100 square feet of root area.

Gardening Know How’s step-by-step is the one to follow:

• Water the soil first if it’s dry — never apply fertilizer to drought-stressed plants.
• Pull back any mulch so the granules reach the soil.
• Sprinkle the fertilizer evenly around the tree’s perimeter, keeping granules well away from the trunk.
• Water thoroughly afterward to work the granules in.
• Time the feeding just before a good rainfall, which helps carry nutrients to the roots.

Epic Gardening confirms the same method: measure the granular fertilizer and sprinkle it in an even coat around the tree’s drip line — the area beneath the outermost reach of the branches, where the feeder roots live.

For newly planted arborvitae, skip the surface feeding. Instead, Gardening Know How notes that fertilizer can go in the backfill or at the bottom of the planting hole before the tree goes in — though only if a soil test shows the need. Otherwise, let new trees establish without fertilizer for the first season.

Common Fertilizing Mistakes To Avoid

• Fertilizing against the trunk. Keep granules away from the bark; concentrated fertilizer there can burn the tree. The root zone at the drip line is where the feeder roots are.
• Fertilizing drought-stressed trees. A dry tree can’t safely take up fertilizer. Water first if the soil is dry, and never feed a tree that’s already struggling with moisture stress.
• Feeding newly planted arborvitae. New trees need to establish roots, not push foliage. Skip fertilizer unless a soil test shows a clear need.
• Late-season feeding. Fertilizing after midsummer stimulates soft new growth that won’t harden before winter — a classic cause of winter burn.
• Overapplying. More fertilizer doesn’t mean more growth. Concentrated zones damage feeder roots, and excess nitrogen can burn the tree or leach into groundwater.

One spring feeding is typically all an established arborvitae needs. If the soil test shows no deficiency and the tree sits in a fertilized lawn, skip the extra feeding entirely — the tree is already getting what it needs.