How to Fertilize Arborvitae Trees? | One Spring Feeding Does It

Fertilize arborvitae trees once a year in early spring with a slow-release, high-nitrogen granular fertilizer like 20-15-15 or 10-5-5, spread at a rate of 1 pound per 100 square feet of the canopy drip line.

Getting the feeding right for your arborvitae isn’t complicated, but it is easy to get wrong. The most common mistake actually kills trees: timing. You only need one application per year, and if you miss the window in early spring, it is better to skip the season than to fertilize late and risk winter damage. This guide covers exactly when to apply, which fertilizer to use, and how to spread it so your trees stay dense and green without root burn.

When Should You Fertilize Arborvitae?

Early spring, before new green growth appears, is the only window you really need. In most US regions that means March through early May, before the summer heat arrives. Fertilizing once at this point supplies all the nutrients the tree needs for the entire growing season.

What Is the Best Fertilizer for Arborvitae?

A slow-release granular fertilizer with higher nitrogen than phosphorus or potassium works best. Look for NPK ratios like 20-15-15, 10-5-5, or a balanced 10-10-10. These formulas support dense green foliage without pushing weak, leggy growth.

How to Apply Fertilizer to Arborvitae Trees

The steps are straightforward, but the details matter. Here is the process that keeps your trees healthy and avoids fertilizer burn.

Step 1: Check Soil Moisture

If the soil around the tree is dry, water it lightly until damp before you spread any fertilizer. Applying dry granular fertilizer to dry soil is the fastest path to root burn.

Step 2: Clear Debris and Pull Back Mulch

Rake away weeds, leaves, and old debris from the entire area under the tree’s canopy. If you have mulch, pull it back so the fertilizer lands on bare soil.

Step 3: Measure the Right Amount

Calculate the root zone by measuring the area under the tree’s widest branches — the drip line.

Step 4: Apply Evenly

Spread the granules in a circle around the tree, keeping them 6 to 8 inches away from the trunk to prevent trunk burn. Cover the whole area under the canopy evenly.

Step 5: Water Thoroughly

After spreading, water the area well to help the fertilizer soak into the root zone. Then replace the mulch you pulled back earlier. If you want to pick the best mulch for this job, our tested roundup of top-rated arborvitae mulches covers exactly which ones improve soil health and suppress weeds.

What Arborvitae Fertilizer Ratios Actually Matter?

The three numbers on a fertilizer bag represent nitrogen, phosphorus, and potassium. For arborvitae, nitrogen is the most important because it drives leaf and stem growth. University of Connecticut extension specialists recommend high-nitrogen formulas like 20-15-15 or 10-5-5 for these evergreens, while UConn’s arborvitae care guide notes that a balanced 10-10-10 works when slow-release is used.

Common Mistakes That Damage Arborvitae

Several well-intentioned habits harm these trees more than neglect. Here is what to avoid.

• Fertilizing new plants: Never add fertilizer to the planting hole or backfill soil. Newly planted arborvitae need no food for the first year — the roots are too tender and the existing soil has enough nutrients to settle in.
• Fertilizing drought-stressed trees: If your trees are dry and wilted, feeding them will burn the roots. Water deeply and wait until the tree recovers before applying any fertilizer.
• Applying after summer’s first day: Fertilizing from late June onward pushes soft new growth that will not harden before frost. That tender growth often dies over winter and can take the whole branch with it.
• Scratching fertilizer into soil: Arborvitae have shallow, surface-level roots. Digging or scratching fertilizer in damages those roots. Instead, just spread granules on the surface and water them in.
• Getting granules against the trunk: Fertilizer touching the trunk causes bark damage and can create entry points for pests. Keep the ring of granules well away from the main stem.

Should You Fertilize Arborvitae in Fall?

A very light feeding in early fall — no earlier than mid-September — is acceptable in mild climates, but you must stop at least one month before the first expected frost. For most gardeners, skipping the fall application entirely is safer. The one spring feeding gives the tree everything it needs.

Do You Need to Fertilize Arborvitae Every Year?

Only if the tree shows signs of needing it. If your arborvitae has dark green needles, puts on 6 to 12 inches of new growth each year, and shows no browning or thinning, it does not need fertilizer. Apply fertilizer only when growth is slow, needles turn yellow or brown, or after the tree has been damaged by insects or disease.

Fertilizer Application Methods Compared

Final Checklist: Fertilize Arborvitae the Right Way

Feed once in early spring before new growth starts. Use a slow-release, high-nitrogen granular fertilizer. Spread 1 pound per 100 square feet of the canopy area, keeping granules 6 inches from the trunk. Water thoroughly after application. Skip fertilization for new trees, drought-stressed plants, or trees with healthy growth. Stop fertilizing after the summer solstice.