Incense cedar

Care Guide: Planting, Soil & Watering

Overview: A large, drought-tolerant conifer that prefers a deep, well-drained, neutral-to-acidic soil in full sun. Once established it needs little water, though young trees appreciate regular moisture.

Quick Care Requirements

Requirement	Ideal Condition
Planting Season	Spring, summer or autumn
Growth Rate	Moderate to Fast
Soil Type	Well-draining, neutral to slightly acidic
Water Need	Low to Moderate – drought-tolerant once established

Planting & Establishment

• Best Planting Season: Plant in spring, summer or autumn while the soil is workable and not frozen.
• How to Plant:
  • Hole Preparation: Dig a hole about twice the width of the root ball but no deeper, so the tree sits at its original level.
  • Soil Amendments: Loosen the backfill; this adaptable tree needs little enrichment, just good drainage.
  • Planting Depth: Set the root collar at grade; never bury the trunk.
• Growth Speed & Expectations: Moderate to fast, developing into a tall, columnar tree over time.

Soil, Watering & Drainage Care

• Soil Mix & Drainage Needs: Needs good drainage and tolerates poorer soils, but not waterlogging.
• Watering Schedule & Technique:
  • Young / Newly Planted: Water regularly through the first seasons to establish a deep root system.
  • Established: Water deeply but infrequently; it is drought tolerant once mature.
  • Seasonal Adjustments: More water in the first summers, much less once established and in winter.

Growing in Pots, Balconies & Indoors

The incense cedar (Calocedrus decurrens) is a large landscape conifer, reaching 20-60 m (60-200 ft). The grower marks it as neither a houseplant nor a container plant – it is a forest tree for open ground in full sun. It is one of the taller conifers here, unsuited to long-term container life. Pots can only ever suit a very young specimen for a few years before it needs to be planted out.

Quick Details

• Container Size: Not recommended long-term; only a large tub for a young specimen, then plant out
• Indoor Suitability: Not a houseplant – a hardy outdoor forest tree
• Best Spot: Outdoors in full sun, in the open ground
• Soil & Drainage: Deep, free-draining loam-based soil; strong drainage holes if potted young
• Watering in Pots: Keep the mix just moist while young; it drains faster than open ground

Indoors & On the Windowsill

• Not a houseplant: The grower marks it as unsuitable indoors – it needs cool seasons, strong light and room to grow into a large tree, and will not tolerate warm, dry indoor air.
• Cold-hardy: Being hardy, it needs no indoor overwintering – it prefers to stay outside year-round.

On a Balcony or Patio

• Only while young: A young plant can spend a few years in a large tub on a patio, but it will soon outgrow any container and need open ground.
• Practicalities: Keep any large tub heavy and stable against wind, water well as pots dry faster than open soil, and plan to plant it out before the roots become cramped.

Choosing the Pot, Soil & Long-Term Care

• A landscape tree, not a long-term pot plant: The grower’s guidance is that this conifer is grown in open ground; a container only holds a young specimen temporarily.
• If potting a young tree: Use a large tub with strong drainage holes and a loam-based mix with added grit; feed through the growing season, as pot nutrients leach faster, then move it to the ground.

Bloom & Flower Guide

Quick Details

• Bloom Season: Spring to summer
• Flower Appearance: Tiny yellow-brown pollen cones scattered at the tips of the sprays — the grower aptly likens them to “dandruff”
• Edibility: Ornamental / none — grown for foliage and fragrance

Detailed Blooming Overview

Incense cedar is a conifer and has no true flowers. In late winter to spring the branch tips carry a scatter of tiny yellow-brown pollen cones — so small and numerous the grower compares them to dandruff. Small woody female cones follow and ripen to a slender, flask-like shape.

Flower Characteristics

• Male pollen cones are tiny, yellow-brown, and borne at the tips of the flat foliage sprays.
• Female cones are small and woody, ripening to an elongated flask shape.

Bloom Care & Thinning

• Nothing to deadhead: The cones need no thinning — they develop and shed on their own.
• Pollination: Wind carries the pollen; no insects are involved.
• Placement: A drought-tolerant tree once established; give it full sun and space to mature.

Pruning, Training & Seasonal Maintenance

Incense cedar grows as a tall, narrow, cone-shaped tree that can eventually reach 20–60 m, and its own care notes point to a specific, real maintenance task: removing branches that droop or grow downward, which keeps the tree’s characteristic upright form and clears lower growth for pedestrian or vehicle clearance as it matures. Pruning tolerance is otherwise low – like most true conifers, it does not resprout from cut-back bare wood, so beyond removing downward-drooping or dead branches, the natural cone-shaped habit should be left alone.

Quick Pruning & Maintenance Specs

Pruning Tolerance	Low
Primary Pruning Window	Cooler months, outside the active growth flush
Typical Frequency	Occasional, as drooping or dead branches appear
Main Objective	Remove downward-growing/drooping branches; maintain a single leader
Young Plant Priority	Correct competing leaders; begin removing low, drooping branches for future clearance
Mature Plant Priority	Continue removing drooping lower branches for clearance; remove deadwood
Best Tool Type	Pruning saw for larger drooping limbs; pole pruner once the tree is tall
Avoid Heavy Pruning During	Any cutting into bare wood behind the green zone – it will not resprout

Pruning by Plant Age & Size

Newly Established

Remove only transplant damage; do not shape.

Young / Formative

Central leader training – correct any competing leader early. Begin selectively removing branches that grow downward rather than outward/upward, as noted for this species, to establish good form and future clearance while cuts are still small.

Mature / Established

Continue removing drooping or downward branches as they appear, plus any deadwood; do not attempt to reduce the tree’s overall size, since it will not resprout from bare wood.

Seasonal Pruning Schedule

Dormant/Winter

Objective: form and clearance. Remove downward-growing branches and deadwood. Do not remove healthy outward/upward-growing branches. Expected response: a cleaner, more upright cone-shaped silhouette.

Structural Pruning & Training

The defining structural task for this species is removing branches that grow down rather than out, which otherwise spoil its narrow, upright profile; leader correction while young supports the same single-trunk form.

Special Growth to Remove

Downward-growing or drooping branches (this species’ own noted issue); a competing leader on a young tree; deadwood at any age.

Tools

A pruning saw for removing drooping limbs once they are more than twig-sized; a pole pruner becomes useful once the tree has grown tall and lower clearance work is out of reach.

Tool Hygiene & Disease Risk

Routine: clean, sharp tools are sufficient; this species’ only noted pest (Syntexis libocedrii, a wood-boring wasp) is not spread by pruning tools, so no special disinfection protocol is needed.

Cut Placement & Technique

Cut drooping branches back to their point of origin at the trunk or a main limb, just outside the branch collar, rather than leaving a stub.

Heavy Pruning & Rejuvenation

Not tolerated – this species does not resprout from bare wood, so there is no way to reduce an oversized tree; size should be anticipated at planting given its eventual large scale.

Post-Pruning Care

No extra feeding needed after routine branch removal; check larger cut wounds occasionally for insect entry, given the wood-boring pest noted for this species.

Common Pruning Mistakes

Leaving drooping branches unaddressed until they are large, requiring bigger, more disfiguring cuts; removing healthy upward-growing branches instead of the downward ones that actually need attention; attempting to reduce the tree’s height expecting regrowth.

When NOT to Prune

Do not cut into bare wood expecting resprouting; avoid major branch removal during active spring growth when wounds are slower to seal.

Recommended Tools (by task)

• Pruning saw – for removing drooping/downward-growing branches, this species’ primary pruning task.
• Pole pruner – warranted once this large, fast-to-medium growing tree matures and clearance cuts are out of reach.

Pruning Troubleshooting

Problem	Possible Cause	What to Check	Corrective Action
Tree losing its narrow, upright cone shape	Downward-growing branches left unaddressed	Lower and mid-canopy branch angles	Remove downward-growing branches back to their point of origin
Small holes or dieback in wood	Syntexis libocedrii (a wood-boring pest noted for this species)	Cut surfaces and trunk for boring holes	Remove and dispose of affected wood; avoid unnecessary wounding that invites entry
Bare gap after a branch was removed	Cut made into wood too far back from the green zone	Whether the cut was on old, leafless wood	None – accept the gap; make future cuts closer to actively growing tissue

Pests, Diseases & Troubleshooting

Overview: Incense cedar is a large, long-lived and notably tough conifer with very few serious pests or diseases when grown in a suitable site. Healthy, vigorous trees shrug off most trouble; problems arise mainly on drought-stressed, injured or poorly sited trees, where bark beetles, scale and root or heart rots can take hold. The best defence is keeping the tree unstressed and well drained.

Quick Troubleshooting Overview

Issue / Pest	Main Symptom	Primary Solution
Cedar bark beetles	Fading flagging branches, dieback	Keep tree vigorous, prune out, remove wood
Scale insects	Bumps on foliage, sooty mould	Horticultural oil, encourage predators
Spider mites	Dull, bronzed, speckled foliage	Hose off, oil in dry spells
Incense-cedar rust	Orange gelatinous galls / brooms	Prune galls, separate from apple/pear hosts
Heart / root rot	Decay, dead limbs, unstable trunk	Avoid wounds, improve drainage, arborist check
Branch flagging	Scattered brown branchlets	Often natural leaf-shed; check if widespread

Common Pests & Management

• Cedar / cypress bark beetles (Phloeosinus species):
  • Symptoms: Small beetles that tunnel under the bark of stressed trees; the first sign is ‘flagging’ — scattered branch tips fading to red-brown — followed by dieback, with tiny entry holes and boring dust on affected limbs.
  • Prevention & Control: Keep trees vigorous and well watered, as beetles target stressed wood. Prune out and remove or chip infested branches promptly (do not leave cut cedar wood nearby as breeding material); avoid injuring the trunk. Insecticides are rarely justified on healthy garden trees.
• Scale insects (Carulaspis and other conifer scales):
  • Symptoms: Small round or oyster-shaped waxy bumps on foliage and twigs; heavy infestations yellow the foliage, and honeydew from soft scales brings sticky sooty mould.
  • Prevention & Control: Encourage natural predators and parasitoids, which usually keep scale in check. On accessible branches apply horticultural oil to smother scale and crawlers, timing sprays to the vulnerable crawler stage; prune out badly encrusted growth.
• Spider mites (Oligonychus and Tetranychus species):
  • Symptoms: Fine stippling, a dull bronzed cast to the foliage and delicate webbing in hot, dry, dusty conditions, especially on young or hedge-clipped trees.
  • Prevention & Control: Hose down the foliage to dislodge mites and reduce dust, and keep trees watered in drought. Treat serious outbreaks with horticultural oil; avoid broad insecticides that kill the mites’ natural predators.
• Cedar wood wasp (Syntexis libocedri):
  • Symptoms: An obscure, mostly harmless relative of sawflies that lays eggs in fire-scorched or freshly dead incense-cedar wood; larvae bore in already-dying or burnt wood rather than attacking healthy trees.
  • Prevention & Control: No control is needed on living, healthy trees — this insect is associated with fire-damaged or dead timber. Simply remove badly burnt or dead wood if present; it poses no threat to a sound garden specimen.

Diseases & Fungal Issues

• Incense-cedar rust (pear/cedar broom rust) (Gymnosporangium libocedri):
  • Symptoms: Orange, gelatinous horn-like galls on the branches in wet weather and dense, congested ‘witches’ brooms’ of distorted growth; the fungus alternates between incense cedar and pome fruits (apple, pear, hawthorn).
  • Treatment & Management: Prune out galls and brooms where practical and remove nearby unmanaged apple, pear or hawthorn hosts to break the cycle. It is rarely fatal to a large cedar; on valued trees a preventive fungicide can be used during wet spring weather.
• Heart rot and wood decay (Oligoporus / Postia and other bracket fungi):
  • Symptoms: Interior decay of old, wounded or storm-damaged trunks and limbs, shown by bracket fungi on the bark, dead limbs and hollowing that weakens the tree.
  • Treatment & Management: Prevention is key: avoid wounding the trunk, prune correctly to promote good sealing, and remove dead and hazardous limbs. Have large or leaning old trees assessed by an arborist for structural safety.
• Root rot in wet soils (Phytophthora / Armillaria species):
  • Symptoms: Poorly drained or over-irrigated sites can rot the roots, giving thin, off-colour foliage, dieback and instability, sometimes with fungal sheets or mushrooms at the base.
  • Treatment & Management: Plant on well-drained ground and avoid heavy irrigation against the trunk. Remove severely affected trees; improve drainage before replanting and keep future trees unstressed.

Growing Difficulties & Abiotic Problems

• Natural branchlet shedding (flagging):
  • Cause & Symptoms: Incense cedar naturally sheds some interior branchlets, which brown and drop; scattered brown flat sprays in the crown are usually normal, not disease.
  • Correction Strategy: Distinguish this from pest flagging: normal shedding is diffuse and seasonal. Simply let the debris fall or clear it; no treatment is needed unless whole living branches are dying.
• Drought stress:
  • Cause & Symptoms: Prolonged drought thins and browns foliage and, crucially, predisposes the tree to bark-beetle attack.
  • Correction Strategy: Water young and newly planted trees deeply during dry spells and mulch the root zone; established trees in suitable sites are very drought tolerant once mature.
• Poor drainage / waterlogging:
  • Cause & Symptoms: Constantly wet, compacted soil rots the roots and stresses the tree, leading to dieback.
  • Correction Strategy: Site on free-draining ground, avoid low wet spots and do not over-irrigate; improve drainage before planting on heavy soils.
• Transplant and site stress:
  • Cause & Symptoms: Recently moved trees or those in cramped, compacted or reflected-heat sites may brown and struggle to establish.
  • Correction Strategy: Give ample room, water consistently through establishment, mulch, and avoid soil compaction and trunk damage around the root zone.

What Helps — Products & Tools

This is a robust tree that seldom needs chemical intervention. The main tools are cultural: deep watering in drought, mulch, sound pruning and prompt removal of infested or dead wood to deny bark beetles breeding material. Horticultural oil handles scale and mites on reachable branches, and a preventive fungicide is only occasionally justified for rust on valued specimens. Use an arborist for large trees.

Propagation Guide

Incense cedar is propagated from seed, the standard and essentially only practical method for this species; vegetative propagation is not needed and is not commonly used for it. Difficulty is Moderate, largely because germination can be slow and uneven.

Quick Propagation Specs

Best Propagation Method	Seed
Propagation Difficulty	Moderate
Seed True-to-Type	Usually true-to-type
Best Propagation Season	Spring sowing
Seed Germination Time	Typically several weeks to a few months, and can be uneven
Germination Temperature	Roughly 10–20°C (50–68°F) after stratification
Seed Sowing Depth	Shallow, about 0.5–1 cm (0.2–0.4 inch), lightly covered

Growing from Seed

Seed Handling & Viability

Seed is best sown reasonably fresh, or given cool, dry storage if held over winter.

Dormancy & Pre-Sowing Treatment

Like many conifers in this family, germination is often improved and made more even with a period of cold, moist stratification before sowing.

Sowing Season

Spring, after stratification.

Sowing Depth & Orientation

Sow shallowly with a light covering of well-drained mix, matching this species’ preference for neutral-to-acid, well-drained soil noted in site data.

Germination Conditions

A cool nursery bed or cold frame with well-drained soil kept evenly moist; germination is naturally variable in percentage and timing for this species.

Germination Time

Typically several weeks to a few months, and can be uneven; low or staggered germination is not unusual.

Seedling Care

Young trees grow slowly at first and benefit from well-drained, neutral-to-acid soil and some protection from harsh sun while establishing.