Getting the timing wrong on arborvitae fertilizer can undo a whole season of growth. Feed too late in the year, and the tender new shoots that result will freeze back when cold weather hits. Feed too early, and the nutrients wash away before the roots can use them. The sweet spot for almost every US yard is a single application in early spring, just before the buds swell.
When To Fertilize Arborvitae: Spring vs. Fall
The primary window runs from March through early April, before new growth emerges. This is when the plant’s roots are waking up and ready to take up nutrients. Fertilizing after the summer solstice (roughly June 20–22) is risky in most areas because it pushes growth that won’t harden off before frost.
Fall fertilization is only worth considering in mild-winter climates, and even then the rules are tight: apply no earlier than mid-September, and stop at least one month before the first expected frost. In severe winter regions, skip fall feeding entirely — the flush of growth it triggers is the most common cause of winter dieback in arborvitae.
What Type of Arborvitae Fertilizer To Use
A slow-release granular fertilizer with a high first number (nitrogen) works best for established trees. Look for ratios like 20‑15‑15, 10‑5‑5, or a balanced 10‑10‑10 where the nitrogen value is the highest. Avoid formulas designed for acid-loving plants like azaleas — UConn’s arborvitae fact sheet recommends evergreen-specific blends instead.
For a concrete product recommendation, our tested roundup of the best arborvitae fertilizers covers the top slow-release options for spring application, including exact NPK values and coverage rates. Trees planted in a lawn that gets regular fertilizer likely don’t need extra feeding — the grass feeding already covers them.
How To Apply Fertilizer Without Damaging The Tree
Root burn is the biggest risk, and it comes from two mistakes: putting granules too close to the trunk, or failing to water them in. Follow this sequence for any established arborvitae:
- Water the soil around the tree thoroughly before you start. Moist soil helps dissolve the granules and prevents root burn.
- Pull back any mulch from the base so you’re applying to bare soil, not on top of bark chips.
- Spread the granules evenly from the trunk area out to the drip line — the outermost edge of the canopy. Keep granules at least a few inches away from the trunk itself.
- Water everything in immediately after spreading, or time the application just before a good rainfall.
When NOT To Fertilize Arborvitae
Never fertilize a newly planted arborvitae in its first year — the shallow, developing roots will burn from the nitrogen concentration. Let the tree settle into nutrient-rich soil instead. Also skip fertilizer if the tree is drought-stressed, if the ground is frozen, or if a frost is forecast within 30 days. Over-fertilizing with excess nitrogen forces weak, unsupported growth and makes the plant more vulnerable to disease.
FAQs
Can I use a balanced lawn fertilizer on arborvitae?
A lawn fertilizer with a high nitrogen content can work, but only if it’s slow-release. Fast-release lawn formulas can burn arborvitae roots, especially if applied near the trunk. Stick with an evergreen-specific blend when possible.
Should I fertilize arborvitae in August?
No. August is past the safe window in all but the mildest climates. Any fertilizer applied after midsummer pushes late growth that won’t survive winter. Wait until the following early spring.
How do I tell if my arborvitae needs fertilizer?
Look for pale or yellowing foliage, stunted new growth compared to previous years, or needles dropping from the interior branches. Healthy arborvitae hold deep green color and put out 4–8 inches of new growth each year. A soil test is the only way to confirm a deficiency.
References & Sources
- UConn Home & Garden Education Center. “Arborvitae Fact Sheet.” Covers fertilization timing, application methods, and NPK recommendations for arborvitae.