Fertiliser for Hydrangeas: How to Grow, Feed, and Care for Vibrant Blooms in Australian Gardens

Hydrangeas are one of the most beloved flowering shrubs in Australia—admired for their show-stopping blooms, lush foliage, and ability to shift flower colour based on soil pH. Whether you’re growing them in garden beds or pots, success comes from understanding their unique needs: light, soil, moisture, pruning—and proper feeding.

Hydrangea Types and Growing Habits

The most common hydrangeas in Australian gardens include:

Hydrangea macrophylla (Bigleaf): Known for mophead or lacecap flowers. Flower colour changes with soil pH—blue in acidic soil, pink in alkaline.
Hydrangea paniculata: Cone-shaped blooms that begin white and fade to pink; thrives in full sun and handles heat well.
Hydrangea quercifolia (Oakleaf): Distinctive foliage and upright flower spikes; excellent for shaded or woodland-style gardens.

Hydrangeas typically flower from late spring through summer. Most varieties grow between 1 and 2.5 metres tall and wide, making them ideal as borders, hedges, or focal points in pots.

Ideal Conditions:

Light: Morning sun with afternoon shade is best. In cooler zones, they can tolerate more direct sun with adequate water.
Soil: Moist, rich, well-draining soil with high organic content. Acidic conditions (pH 5.5–6.0) are ideal for blue blooms.
Water: Deep water 2–3 times a week during active growth. Avoid shallow watering, which leads to weak root systems.

Hydrangeas are shallow-rooted, so mulch well and avoid disturbing the soil around the base. In pots, choose wide containers and use premium potting mix with good moisture retention.

Pot-Grown Hydrangea Tips:

Use a large (at least 40cm wide) pot with good drainage holes.
Mix in organic matter or coconut coir to improve water retention.
Feed and water more regularly than garden-grown hydrangeas.

What is the Best Fertiliser for Hydrangeas?

Feeding hydrangeas correctly is crucial for bold flowers, strong stems, and long-lasting leaf colour. Using the wrong fertiliser—especially those too high in nitrogen—can result in lush green growth but little to no flowering.

What Fertiliser is Good for Hydrangeas?

The ideal hydrangea fertiliser contains:

Low to moderate nitrogen (N): Prevents overly leafy growth and encourages bud development
Higher phosphorus (P): Supports flower size, colour, and formation
Ample potassium (K): Improves stem strength and water balance
Micronutrients: Iron and magnesium help prevent leaf yellowing and support flower pigmentation

Recommended Fertilisers from Complete Grow:

Advanced NPK 4-18-38 + Cal-Mag – Ideal for flowering stage. The high phosphorus boosts bloom quality while calcium and magnesium prevent leaf curl and improve plant resilience.
NPK 20-20-20 Liquid Fertiliser – A balanced, all-purpose option for early-season growth, especially when establishing new plants.

Both fertilisers are:

Water-soluble and fast-absorbing
pH-buffered and chloride-free
Suitable for garden soil, raised beds, and pots

For blue blooms, ensure your soil remains acidic. You can combine fertiliser use with pH control methods like:

Adding elemental sulfur or aluminium sulfate
Avoiding lime or alkaline composts
Feeding with soft water or rainwater (tap water can raise pH)

Hydrangea Care: When to Fertilise, Cut Back, and Maintain Your Plant Year-Round

Feeding hydrangeas without overdoing it is key to success. Below is a general schedule that suits most Australian climates:

Feeding Schedule:

Early Spring: Apply NPK 20-20-20 at half strength to support leafy regrowth and root energy after dormancy.
Mid-Late Spring: Switch to NPK 4-18-38 to boost flowering. Feed every 3–4 weeks until blooms fade.
Summer: Maintain with light feeding and deep watering. Mulch to retain moisture.
Autumn: Stop fertilising. Allow plant to harden off before winter. Begin pruning only if the plant flowers on new wood.

Pruning Tips:

Macrophylla (mophead/lacecap): Prune only after flowering. Do not cut back hard, or you risk removing next year’s buds.
Paniculata and arborescens: Prune in late winter/early spring. These bloom on new wood.
Oakleaf: Minimal pruning required. Remove dead stems or shape in early spring.

Common Problems & Fixes:

Pale leaves: Check for iron deficiency. Add a liquid Cal-Mag blend or foliar iron supplement.
No blooms: May be over-pruned or overfed with nitrogen. Reduce nitrogen and prune less aggressively.
Wilting in heat: Apply mulch, water deeply in the morning, and provide temporary shade in extreme conditions.

With consistent care, the right feeding strategy, and proper pruning, your hydrangeas will reward you with stunning displays year after year.