Holmstrup Arborvitae (Columnar Thuja) care

Light

Aim for at least 4-6 hours of direct sun on the leaves. Full sun for the densest column and best colour; tolerates light shade but grows looser and slower with under 6 hours of direct sun. If your only bright window faces south, that's perfect for holmstrup arborvitae — same window any aroid would fry on.

Watering

Watering holmstrup arborvitae: two to three times weekly when young; weekly once established. The number that matters isn't the day of the week — it's how dry the top 2-3 cm of the pot feels. A finger in the soil tells you more than a watering app. After every watering, tip the saucer. Maintain even soil moisture, particularly the first two seasons and during dry spells. Mulch the root zone; avoid both drought stress and standing water.

Soil and pot

Holmstrup Arborvitae grows best in moist, fertile, well-drained loam. Adaptable across soil types but prefers neutral to slightly alkaline, evenly moist ground with reliable drainage. Enrich poor soils with organic matter. A pot with a working drainage hole is non-negotiable for this species — even free-draining mix will turn soggy in a closed planter. If you love the look of a decorative pot without a hole, use it as a cachepot around an inner nursery pot you can lift out to water.

Humidity and temperature

Holmstrup Arborvitae sits happiest at around Ambient outdoor humidity humidity and -37 to 30°C (-35 to 86°F). An outdoor screening conifer unaffected by humidity; allow airflow between plants to reduce fungal foliage blight in humid climates. If you keep the room above year-round and avoid placing the plant near a cold draught, a hot radiator, or an air-conditioning vent, you have already handled the two biggest indoor stressors.

Fertilising

Feed holmstrup arborvitae sparingly. Feed once in early spring with a balanced slow-release or evergreen fertiliser. A light second feed in early summer helps young hedge plants; avoid late-season nitrogen that encourages frost-tender growth. Skip fertiliser entirely on a stressed, recently-repotted, or actively wilting plant — fertiliser salts make damage worse, not better. Wait for a round of healthy new growth before resuming a feeding rhythm.

Common problems

Below are the issues we see most often on holmstrup arborvitae in the Growli community. Each is annotated with the most common cause so you know where to start.

• Winter browning — Drying winter wind and frozen soil can bleach foliage; water deeply before freeze-up and shelter exposed plants.
• Snow/ice splaying — Heavy snow load can splay the narrow column; tie multi-stem plants loosely and brush off heavy snow.
• Bagworms — Camouflaged silk bags strip foliage; remove by hand in winter or treat young larvae in early summer.
• Drought-induced interior browning — Dry spells brown inner foliage; consistent watering and mulch keep the column dense and green.

Propagation

Propagated from semi-hardwood cuttings taken in late summer or autumn, treated with rooting hormone in a humid frame or under mist. Cuttings root well and reproduce the cultivar true; seed will not. Propagation is the cheapest, most satisfying way to expand a collection — and it doubles as insurance against losing a mature plant to an accident. Take a backup cutting once the parent is established and healthy.

Toxicity to pets

Holmstrup Arborvitae is mildly toxic to pets. Thuja occidentalis is not individually listed on the ASPCA toxic or non-toxic plant lists; treat with caution and verify with a vet. Foliage and oil contain thujone, which in quantity can cause drooling, vomiting, diarrhoea, and in severe cases neurological signs in dogs and cats. Poisonings are uncommon, but ingestion should be prevented and monitored. If you keep cats, dogs, or curious children in the house, weigh placement carefully — a high shelf or a hanging planter is enough for casual safety. For severe ingestion incidents, call your local vet and the ASPCA Animal Poison Control Center (in the US, 888-426-4435).

Pet-safety status is sourced from the ASPCA Toxic and Non-Toxic Plant List, which catalogues the most-asked-about plants for cats, dogs, and horses.

Holmstrup Arborvitae deep-dive guides

Every aspect of holmstrup arborvitae care, each with its own calibrated guide:

• Holmstrup Arborvitae watering schedule
• Holmstrup Arborvitae light requirements
• Best soil mix for holmstrup arborvitae
• Holmstrup Arborvitae fertilizing guide
• When to repot holmstrup arborvitae
• How to propagate holmstrup arborvitae
• Holmstrup Arborvitae growth rate & size
• Holmstrup Arborvitae cold hardiness
• Holmstrup Arborvitae temperature & humidity
• Is holmstrup arborvitae toxic to cats & dogs?
• Is holmstrup arborvitae toxic to cats?
• Is holmstrup arborvitae toxic to dogs?
• Getting holmstrup arborvitae to bloom

Featured in these plant shortlists

Holmstrup Arborvitae qualifies for 4 curated Growli shortlists — each one filtered objectively from our structured plant-care library, so the selection is consistent and checkable:

• Best drought-tolerant houseplants — Houseplants that prefer to dry out — forgiving of forgotten watering and ideal for travel or busy weeks.
• Best flowering houseplants — Indoor plants grown for their blooms — selected from the flowering species in Growli’s plant-care library.
• Best houseplants for full sun — Houseplants that want direct sun — the species for a hot south or west-facing windowsill where shade-lovers scorch.
• Best houseplants for a cool room — Houseplants that tolerate cool conditions down to about 10°C — for an unheated spare room, hallway, porch or a home kept cool.
• Browse all 29 plant shortlists — pet-safe, low-light, drought-tolerant and more

Related guides

Holmstrup Arborvitae is also commonly called Holmstrup Arborvitae or Columnar Thuja.

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