Best Fertiliser for Grevilleas

Grevilleas are hardy and beautiful shrubs, but they are very particular about fertiliser. Choosing the wrong type can damage or even kill them, while the right blend ensures lush foliage, long flowering, and resilience to pests and stress.

Why Grevilleas Need Low-Phosphorus Fertiliser

Grevilleas, like many Australian native plants, evolved in phosphorus-deficient soils. Their roots have special adaptations called cluster roots that absorb phosphorus very efficiently. While this helps them survive in poor soils, it also means they are highly sensitive to excess phosphorus. Standard fertilisers with more than 3% P can burn the roots, cause yellowing, or kill the plant.

Core Nutrient Needs

Nitrogen (N): Supports healthy leaf and stem growth. Needed most in spring and after pruning.
Potassium (K): Critical for flowering. Potassium promotes bigger, brighter flower spikes and improves nectar production.
Calcium & Magnesium: Strengthen stems, prevent leaf yellowing, and support long-term root health.
Micronutrients (Iron, Boron, Zinc, Manganese): Prevent common nutrient deficiencies in alkaline or sandy soils.

The best fertiliser for Grevilleas is always a low-phosphorus, high-potassium formula. This combination fuels flowering while keeping roots safe.

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Seasonal Fertiliser Plan for Grevilleas

Grevilleas flower at different times depending on the variety, but consistent feeding keeps them vigorous year-round. Here’s a seasonal guide to fertilising:

Spring: Apply a balanced liquid fertiliser such as CompleteGrow NPK 20-20-20 (diluted) to support leafy growth and set flower buds.
Summer: Switch to CompleteGrow 4-18-38 + CaMg for strong, long-lasting flowers. Its high potassium content boosts nectar and extends blooming.
Autumn: Reapply potassium-rich fertiliser to maintain flowering and harden growth before winter.
Winter: Apply only a light feed. Too much nitrogen in cold months produces soft shoots vulnerable to frost and pests.

Application Tips

Always water plants before fertilising to prevent root burn.
Use liquid fertilisers for quick uptake, especially in pots. Granules release nutrients more slowly.
Apply around the drip line (where rainwater falls from the canopy), not directly on the crown.
Mulch with organic material to retain moisture and protect feeder roots.

Grevilleas in pots need fertiliser more often—every 2–3 weeks—because nutrients leach out with frequent watering.

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Fertiliser Mistakes, Common Problems & FAQ

Common Mistakes to Avoid

Using general garden fertilisers: Most contain high phosphorus, which is toxic to Grevilleas.
Over-fertilising in winter: Encourages weak, frost-sensitive growth.
Neglecting potassium: Leads to poor flower production and reduced nectar output.

Problems Linked to Fertiliser

Yellow Leaves: Often caused by iron or magnesium deficiency—use a complete fertiliser with trace elements.
No Flowers: Usually linked to low potassium or over-pruning. Switch to a bloom booster formula.
Stunted Growth: High-phosphorus fertiliser may have damaged roots. Flush soil with water and switch to a safe formula.

FAQ

Q: What fertiliser should I avoid for Grevilleas?
A: Any with high phosphorus (above 3%). Always choose low-P labelled as “safe for natives.”
Q: How often should I fertilise Grevilleas?
A: Every 4–6 weeks during active growth. In pots, every 2–3 weeks with diluted liquid feed.
Q: Do Grevilleas need special fertiliser for flowers?
A: Yes—choose a high-potassium, low-phosphorus formula like CompleteGrow 4-18-38 + CaMg.
Q: Can fertiliser fix a dying Grevillea?
A: If nutrient deficiency is the issue, yes. But root rot or over-pruning need different solutions.

Final Recommendation: The best fertiliser program for Grevilleas combines CompleteGrow NPK 20-20-20 in spring with CompleteGrow Advanced 4-18-38 + CaMg in summer and autumn. This keeps roots safe, encourages lush foliage, and guarantees abundant, bird-attracting flowers throughout the year.