How to Fertilize Arborvitae (Thuja): Best Fertilizer, Timing and Common Mistakes

Arborvitae, commonly sold under the botanical name Thuja, usually needs less fertilizer than many gardeners assume. Healthy established plants growing in suitable soil may require little or no supplemental feeding, while unnecessary fertilizer can damage roots or encourage tender late-season growth.

The best approach is to judge the plant first: examine growth, foliage color, soil condition, moisture and pH before adding nutrients. A soil test is especially useful when arborvitae is growing poorly or showing unexplained discoloration.

Does arborvitae need fertilizer?

Not always.

University of Maine Cooperative Extension notes that most established trees and shrubs do not require additional fertilizer when they are planted properly and growing normally. Fertilizer should not be the automatic response to every case of yellow or brown foliage.

UConn Extension recommends fertilizing arborvitae in early spring when soil testing or plant performance indicates a need. Trees growing beside regularly fertilized lawns may already receive enough nutrients and may not require a separate application.

This makes arborvitae different from annual flowers or heavy-feeding vegetables: routine feeding several times per season is usually unnecessary.

When should arborvitae be fertilized?

If fertilizer is needed, early spring is generally the best time.

UConn recommends spring application, while University of Maine advises avoiding fertilizer after midsummer because late feeding can stimulate new growth that does not have enough time to harden before winter.

What is the best fertilizer for arborvitae?

There is no single fertilizer formula that every arborvitae requires.

UConn Extension recommends following soil-test results. Where supplemental fertilizer is needed, it gives examples of nitrogen-containing formulations such as 20-15-15 or 10-5-5.

The most important point is not the exact brand or N-P-K ratio, but avoiding unnecessary nutrient applications.

Suitable options may include:

• a granular fertilizer formulated for trees and shrubs;
• a slow-release nitrogen-containing fertilizer;
• finished compost where soil organic matter is low;
• a fertilizer formulation specifically recommended by a soil test.

Do not assume that a product labeled “evergreen fertilizer” is automatically appropriate. The nutrient balance should match the soil and plant condition.

How much fertilizer should arborvitae receive?

UConn Extension gives a general recommendation of one pound of fertilizer per 100 square feet of root area for the example formulations it recommends.

However, the actual amount depends on fertilizer analysis and soil-test results. A concentrated product and a lower-analysis fertilizer cannot be applied at the same weight and expected to deliver the same amount of nitrogen.

Fertilizer should be distributed over the root zone rather than piled around the trunk.

Concentrating fertilizer in a small area can create excessive salt levels and damage feeder roots.

Where should fertilizer be applied?

The active root system of an established arborvitae extends beyond the immediate base of the trunk.

Broadcast granular fertilizer over the soil surface across the root zone rather than placing it in a narrow ring directly against the stem.

UConn recommends surface application over the root system so that nutrients are available to a larger portion of the feeder roots and concentrated fertilizer zones are avoided.

If rainfall is not expected, water appropriately after application according to the fertilizer label.

Do not fertilize drought-stressed arborvitae

This is one of the most important mistakes to avoid.

Fertilizers contain soluble salts. When soil moisture is already low, fertilizer can increase stress on roots rather than solve the underlying problem.

University of Maine and University of New Hampshire Extension both advise against fertilizing drought-stressed woody plants.

Restore proper soil moisture first and determine whether the foliage problem is actually caused by drought.

What soil pH does arborvitae prefer?

Arborvitae tolerates a relatively broad soil pH range.

UConn lists approximately pH 6.0 to 8.0 as suitable, while University of New Hampshire describes arborvitae as preferring approximately pH 6.0 to 7.0.

University of Maine also cautions against automatically acidifying soil around arborvitae. Unlike some other conifers, arborvitae can perform well in neutral to moderately alkaline soil.

This is important because gardeners sometimes assume that every evergreen requires strongly acidic soil.

A soil test should guide any attempt to change pH.

Yellow arborvitae does not automatically mean nutrient deficiency

Yellowing is one of the most common reasons gardeners reach for fertilizer, but foliage discoloration has many possible causes.

These can include:

• drought stress;
• poor drainage or root rot;
• winter injury;
• transplant stress;
• normal seasonal foliage changes;
• spider mites;
• root damage;
• nutrient deficiency.

Virginia Tech notes that some arborvitae cultivars naturally develop yellow-brown or bronze coloration during winter. Cultivars such as ‘Emerald’, ‘Nigra’ and ‘Techny’ tend to retain greener winter foliage than some others.

Applying fertilizer without identifying the cause can therefore make the problem worse.

Can you diagnose nutrient deficiencies from foliage color alone?

Not reliably.

The old version of this article associated specific symptoms such as yellow tops with potassium and magnesium deficiency, white coatings with iron deficiency and brown-purple branch tips with phosphorus deficiency.

These visual symptoms are not sufficiently specific to support a diagnosis by themselves.

Discoloration can result from environmental stress, disease, insects, damaged roots or winter weather. If a true nutrient deficiency is suspected, a soil test and, where appropriate, plant-tissue analysis provide much stronger evidence than color alone.

Watering is often more important than fertilizer

Arborvitae needs adequate soil moisture, particularly during establishment and dry periods.

University of Maine recommends deep watering during dry weather while allowing the soil to approach dryness between waterings rather than keeping the root zone constantly saturated.

Both too little and too much water can cause foliage discoloration.

Poorly drained soil can deprive roots of oxygen and encourage root problems, while prolonged drought can cause browning and dieback.

How much sunlight does arborvitae need?

Full sun generally produces the densest growth.

Virginia Tech describes Eastern arborvitae (Thuja occidentalis) as performing best in full sun. Plants can tolerate some shade, but foliage becomes less dense as available light decreases.

UConn recommends approximately eight hours of direct sunlight for best growth.

No fertilizer can fully compensate for a plant growing in an unsuitable amount of light.

Can compost be used around arborvitae?

Yes, compost can be useful where soil organic matter is low.

Finished compost contributes organic matter and can improve soil structure and water management without delivering the large nutrient pulse associated with concentrated synthetic fertilizer.

A layer of organic mulch can also help reduce moisture loss and moderate soil temperature.

Keep mulch away from direct contact with the trunk. Deep piles against the stem can retain excessive moisture and contribute to bark and root problems.

Should you use manure on arborvitae?

Fresh manure should not be placed around arborvitae roots.

Fresh manure may contain high concentrations of soluble salts and nitrogen and can damage roots.

If manure is used, choose well-composted material and treat it primarily as an organic soil amendment rather than as a reason to apply additional heavy fertilizer.

Should you use wood ash around arborvitae?

Only when soil conditions justify it.

Wood ash contains potassium and calcium but also has a strong liming effect and can raise soil pH quickly.

University of New Hampshire Extension warns that wood ash can increase pH more rapidly than limestone if overapplied.

Because arborvitae already tolerates neutral and moderately alkaline soil, repeatedly spreading ash without testing can push pH unnecessarily high.

Are homemade yeast and herbal fertilizers useful?

There is no strong reason to prefer homemade yeast solutions or fermented herbal mixtures over conventional soil management for arborvitae.

The nutrient concentration of homemade preparations is unpredictable and may vary considerably between batches.

Adding urea or ammonium nitrate to a homemade plant infusion also turns it into a nitrogen fertilizer whose actual application rate becomes difficult to control.

For established woody landscape plants, a soil test and a known fertilizer analysis provide a much more reliable approach.

Does arborvitae need foliar fertilizer?

Routine foliar feeding is unnecessary for most arborvitae.

Woody plants normally obtain the majority of their mineral nutrition through roots.

Foliar nutrient applications can have specialized uses for confirmed micronutrient deficiencies, but repeatedly spraying the foliage every two weeks is not a standard arborvitae-care recommendation.

Why does newly planted arborvitae turn brown?

New plants frequently experience transplant stress while their root systems establish.

University of Maine notes that arborvitae planted late in the season can also suffer winter injury before becoming fully established.

Before fertilizing a recently planted arborvitae, check:

• whether the root ball is drying out;
• whether the planting hole drains properly;
• whether the root flare is at the correct depth;
• whether winter exposure caused damage;
• whether roots established before hot or cold weather.

Adding fertilizer does not correct these planting problems.

Common mistakes when fertilizing arborvitae

Simple arborvitae fertilizer schedule

Frequently asked questions