Fertilising guide
How to fertilise Arborvitae (Thuja occidentalis)— schedule & NPK
Also called arborvitae, eastern arborvitae, American arborvitae, white cedar, eastern white cedar, northern white cedar, tree of life.
More about arborvitae
About Arborvitae
Thuja occidentalis · also called arborvitae, eastern arborvitae · houseplant
Arborvitae is a hardy evergreen conifer grown outdoors for hedging, screening and in large containers. It wants full sun, deep well-drained soil and even moisture while establishing. It is not on the ASPCA list, but its foliage and oils contain thujone — a neurotoxin — so treat it as toxic to pets and livestock and verify any exposure with your vet.
Growth habit: Dense, pyramidal to narrowly columnar evergreen conifer with flattened sprays of scale-like, aromatic foliage that is bright green in summer and may turn bronze in winter. Branches are erect and spreading, giving the formal, sturdy outline prized for clipped hedges and screens.
Watch for — Winter burn / foliage bronzing: Cold, drying winds and winter sun pull moisture from the evergreen foliage faster than frozen roots can replace it, scorching it brown, especially on young or exposed plants.
What fertiliser arborvitae actually wants — and why
Arborvitae is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for arborvitae: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed arborvitae, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For arborvitae:
Feed in early spring with a balanced slow-release fertiliser or one formulated for evergreens/conifers as new growth begins. Established plants in decent soil need little feeding; avoid heavy late-summer feeding, which pushes soft growth vulnerable to winter burn. Container-grown plants need regular feeding through the growing season. Treat that as sparingly through the growing season between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
The dormant-season rule matters more than the exact interval: skip feeding entirely when arborvitae is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for arborvitae
Half strength is the safe default for arborvitae — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
Feeding always goes onto already-damp soil, never dry roots — water arborvitae first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the arborvitae watering schedule.
Signs you are over-feeding arborvitae
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for arborvitae:
- Brown, crispy leaf tips and edges with no sign of underwatering.
- A white, crusty salt deposit on the soil surface or pot rim.
- Weak, pale, stretched new growth that flops.
- Lower leaves yellow and drop while the soil is correctly watered.
Signs you are under-feeding arborvitae
- Uniformly pale or yellow-green leaves, oldest first.
- Noticeably small new leaves and stalled growth in good light and season.
- A generally tired, lacklustre look despite correct watering and light.
If the symptoms point at watering, light or roots rather than nutrition, the full arborvitae care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of arborvitae with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Organic vs synthetic feeds for arborvitae
Organic options
A diluted seaweed or worm-casting feed, or fish emulsion if you can tolerate the smell indoors. UK: Westland or Baby Bio Organic, dilute seaweed; US: Espoma Indoor! or Neptune's Harvest fish & seaweed. Slow, gentle and hard to overdo.
Synthetic / liquid feeds
A general-purpose houseplant liquid at half strength — UK: Baby Bio, Westland Houseplant Feed or Phostrogen; US: Miracle-Gro Indoor Plant Food or Schultz. Convenient and fast-acting; the only risk is overdoing it.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising arborvitae — frequently asked questions
What fertiliser does arborvitae need?
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula. Arborvitae is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
How often should I feed arborvitae?
Feed in early spring with a balanced slow-release fertiliser or one formulated for evergreens/conifers as new growth begins. Established plants in decent soil need little feeding; avoid heavy late-summer feeding, which pushes soft growth vulnerable to winter burn. Container-grown plants need regular feeding through the growing season. Feed in early spring with a balanced slow-release fertiliser or one formulated for evergreens/conifers as new growth begins. Established plants in decent soil need little feeding; avoid heavy late-summer feeding, which pushes soft growth vulnerable to winter burn. Container-grown plants need regular feeding through the growing season. Treat that as sparingly through the growing season between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
What strength of feed for arborvitae?
Half strength is the safe default for arborvitae — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding arborvitae look like?
Brown, crispy leaf tips and edges with no sign of underwatering. A white, crusty salt deposit on the soil surface or pot rim. Weak, pale, stretched new growth that flops. Lower leaves yellow and drop while the soil is correctly watered. Feeding arborvitae year-round on a fixed schedule, including dark winter months, is the most common mistake — it cannot use the nutrients in low light and the surplus simply burns the roots and crusts the soil.
Should I flush the soil of arborvitae?
Flush the pot of arborvitae with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Keep reading
- Arborvitae care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water arborvitae — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise snake plant
- How to fertilise dracaena
- How to fertilise peperomia
- All 271 fertilising guides in the Growli library