Silk Oak

grevillea robusta

Also known as: ["Australian Silver Oak","Silk Tree"]

Family: Proteaceae Genus: Grevillea Category: Trees

Overview

A large, fast-growing tree native to eastern Australia, known for its fern-like leaves and bright orange-red flowers.

Benefits & Perks

["fast growing","fragrant flowers","wildlife attractant (bees, butterflies, birds)","drought tolerant"]

Botanical Classification

Phylum: Magnoliophyta
Class: Magnoliopsida
Order: Proteales
Family: Proteaceae
Genus: Grevillea
Botanical Name: Grevillea robusta

Plant Characteristics

Basic Information
  • Category: Trees
  • Suitable Location: outdoor garden in a sheltered spot with good air circulation
  • Suitable For:
    Outdoor Landscapers Wildlife Supporters
  • Is Weed: No
  • Allergenicity: low
Environmental Needs
  • Climate: {"temperatureRange":"10–35°C"}
  • Hardiness: {"zones":"9–11"}
  • Misting: rarely required, only if ambient humidity is very low
  • Drainage: Fast-draining to prevent root rot.
  • Soil Type: Well-draining, slightly acidic soil with organic matter; cactus or succulent mix is ideal.
Maintenance Level
  • Maintenance Level: moderate
  • Toughness Level: high
  • Pruning Frequency: Annually in late winter or early spring; light pruning can be done after flowering.
  • Pruning Intensity: Moderate; remove up to one-third of old growth to rejuvenate the plant.
Care Details

Ideal Sunlight Coverage:
Full sun to partial shade (4–6 hours of direct sunlight daily); tolerates light shade in hotter climates.

Sunlight Tolerance Tips:
Acclimate plants gradually to intense sunlight; protect from harsh afternoon sun in hot regions; ensure good air circulation to prevent sunburn.

Warning Signs: Yellowing leaves, root rot, or stunted growth indicate poor soil drainage or improper pH.

Care Requirements

Care Difficulty
moderate

moderate

Sunlight

full sun to partial shade

Rotate plant for even light exposure; use shade cloth in extreme heat; avoid placing near reflective surfaces that intensify sunlight.

Watering

every 7–10 days during active growth, reduce in winter

Water thoroughly but infrequently to encourage deep root growth; avoid overwatering, especially in winter; ensure soil dries partially between waterings.

Soil

well-draining, slightly acidic soil

pH: Slightly acidic (pH 5.5–6.5).

Use a mix with good aeration; avoid heavy clay soils; ensure pots have drainage holes.

Temperature

Prefers warm temperatures (65–85°F or 18–29°C); can tolerate mild frosts but thrives in subtropical to tropical climates.

Protect from frost; ensure good air flow in heat; adjust watering with temperature changes.

Fertilizing

every 2–3 months during spring and summer with balanced fertilizer

Apply fertilizer before new growth emerges; avoid high-phosphorus formulas; flush soil occasionally to prevent salt buildup.

Propagation

Methods

Stem cuttings or seed; stem cuttings are more reliable for home growers.

Step-by-Step Propagation Guide
  1. Take 4–6 inch cuttings.
  2. Remove lower leaves.
  3. Dip in rooting hormone.
  4. Plant in medium.
  5. Maintain humidity.
  6. Keep warm and shaded.

Best Time: Spring or early summer when the plant is actively growing.

Environment

Warm (70–75°F or 21–24°C), humid, and partially shaded environment.

Medium

Well-draining mix of perlite and peat moss or cactus mix.

Hormone

Rooting hormone is recommended to improve success rates.

Timeline

Roots may develop in 4–8 weeks; establishment can take several months.

Tools Needed

Pruning shears, rooting hormone, small pots, misting spray bottle.

Quick Tips

Use healthy, non-flowering stems; maintain high humidity with a plastic cover; avoid direct sunlight.

Pruning & Repotting

Pruning Guide
Method

Use clean, sharp tools; make cuts just above a leaf node or lateral branch; avoid excessive pruning of flowering stems.

Pruning Plan

Prune to maintain shape, encourage bushiness, and remove dead or diseased growth.

Tools

Pruning shears, loppers, gloves, disinfectant.

Checklist

Disinfect tools; prune dead/diseased wood; shape the plant; avoid over-pruning.

Repotting Guide
Best Season

Early spring before new growth begins.

Pot Size

Move to a pot one size larger (2–3 inches wider in diameter).

Method

Remove plant gently; trim rootbound roots; replace with fresh, well-draining soil; ensure proper drainage.

Suggestions

Repot every 2–3 years or when roots fill the container; beneficial for younger plants to encourage growth.

Checklist

Choose appropriate pot; prepare fresh soil; inspect roots; water after repotting.

Advanced Care Tips

Watering Mastery
Watering Checklist

Check soil moisture before watering; water deeply; ensure proper drainage; avoid wetting leaves.

How to Apply Water Properly

Water at the base of the plant, targeting the root zone; apply until water drains from the bottom; avoid wetting foliage to prevent fungal issues; water early in the day to minimize evaporation.

Pro Tip: Use a soaker hose or drip irrigation to deliver water directly to the roots with minimal waste.
Watering Schedule Tips

Water deeply once every 7–10 days during active growth in spring and summer; reduce frequency to every 2–3 weeks in fall and winter. Adjust based on rainfall and soil moisture.

Soil Improvement

Add perlite or coarse sand for drainage; incorporate compost for fertility; ensure soil is loose and airy.

Temperature Stress Management
Signs of Temperature Issues

Chlorosis or leaf drop in extreme cold; wilting or scorching in excessive heat.

Cold Stress

Grevillea robusta can suffer leaf drop and root damage if exposed to prolonged temperatures below 25°F (-4°C).

Solution: Provide frost protection with burlap or frost cloth; move potted plants indoors; avoid overwatering during cold spells.

Hot Stress

Leaves may wilt, curl, or develop brown edges in extreme heat; growth may slow.

Solution: Provide afternoon shade; increase watering frequency; use mulch to retain soil moisture; improve air circulation.

Fertilizing Guide
Fertilizing Checklist

Use balanced fertilizer; apply in spring; avoid winter feeding; follow label instructions.

Fertilizing Method

Use a balanced, slow-release fertilizer in spring; dilute liquid fertilizer to half-strength monthly during growing season; avoid fertilizing in winter.

Common Problems & Solutions

Yellowing leaves in Grevillea robusta can indicate nutrient deficiencies, overwatering, or pest infestations, affecting the plant's photosynthetic efficiency and overall health.

Wilting in Grevillea robusta is often a sign of water stress, either due to drought or overwatering, which can lead to root damage and reduced nutrient uptake.

Leaf spots on Grevillea robusta may be caused by fungal or bacterial infections, leading to reduced photosynthesis and potential defoliation if left untreated.

Rotting, particularly root rot, can occur in Grevillea robusta if the soil is poorly drained or excessively moist, leading to decay of root systems and eventual plant death.

Toxicity Warning

Cats
Slightly Toxic

Cats are susceptible to mild to moderate toxicity from Grevillea robusta due to the cyanogenic glycosides in the seeds and leaves. These compounds can impair cellular respiration and cause systemic effects.

⚠️ Symptoms:
vomiting drooling lethargy difficulty breathing tremors
🌿 Toxic Parts:
seeds leaves
⚡ Toxic If:

if eaten

Prevent cats from accessing the plant. Seek veterinary care if ingestion is suspected.
Dogs
Slightly Toxic

In dogs, ingestion of Grevillea robusta seeds and leaves can cause mild to moderate toxicity due to the presence of hydrogen cyanide. The cyanogenic glycosides can disrupt oxygen transport in the body, leading to adverse effects.

⚠️ Symptoms:
vomiting diarrhea lethargy difficulty breathing tremors
🌿 Toxic Parts:
seeds leaves
⚡ Toxic If:

if eaten

Keep pets away from the plant. If ingestion occurs, contact a veterinarian immediately.
Humans
Slightly Toxic

Grevillea robusta contains hydrogen cyanide in its seeds and leaves, which can lead to mild to moderate toxicity upon ingestion. The cyanogenic glycosides release cyanide when the plant material is chewed or crushed, interfering with cellular respiration.

⚠️ Symptoms:
nausea vomiting abdominal pain dizziness weakness
🌿 Toxic Parts:
seeds leaves
⚡ Toxic If:

if eaten

Avoid ingestion of seeds and leaves. Wash hands thoroughly after handling the plant. Keep out of reach of children.
Important: Keep this plant out of reach of children and pets. If ingestion occurs, contact poison control or veterinary services immediately.

Frequently Asked Questions

Q: Is Grevillea robusta suitable for small gardens?

A: No, it is a large tree and requires ample space.

Q: Does it attract wildlife?

A: Yes, it attracts bees, butterflies, and birds with its nectar-rich flowers.

Q: How often should it be watered?

A: Once established, it is drought-tolerant and requires minimal watering.

Quick Reference
Family: Proteaceae
Care: moderate
Light: full sun to partial shade
Water: every 7–10 days during activ
Suitable For: ["outdoor landscapers","wildlife supporters (attracts bees, butterflies, birds)"]
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