Best Fertiliser for Roses

Roses are among the most rewarding plants in any garden, but they are also demanding feeders. A balanced fertiliser program keeps leaves deep green, stems strong, and blooms large and colourful. The right formula nourishes the plant without forcing weak, leafy growth — supporting every stage from root to flower.

The most effective approach combines two balanced formulations:
CompleteGrow All Purpose NPK 20-20-20 for early-season development, and
Advanced NPK 4-18-38 + Calcium & Magnesium for flowering and colour enhancement.
Used together, they maintain steady nutrient flow and produce consistent, repeat flowering.

Understanding Rose Nutrition

Roses use nutrients rapidly through active growth and flowering. Nitrogen supports new leaves and canes, phosphorus strengthens roots and encourages buds, while potassium enhances colour, fragrance, and petal texture. Trace elements like calcium and magnesium keep the plant resilient and prevent leaf discolouration.

Nitrogen (N)

Promotes leafy growth and rich green colour. The balanced nitrogen in 20-20-20 builds healthy stems early in the season without overstimulating foliage at the expense of flowers.

Phosphorus (P)

Drives root strength and new bud formation. The 18% phosphorus in the 4-18-38 formula supports repeat flowering after pruning or heavy bloom periods.

Potassium (K)

Enhances bloom size, depth of colour, and petal firmness. A high potassium blend improves fragrance, extends bloom life, and increases resistance to heat stress.

Calcium & Magnesium

Calcium maintains firm stems and reduces petal drop, while magnesium boosts chlorophyll production for darker leaves. Together they support long-term plant energy and overall appearance.

By alternating 20-20-20 for structure and 4-18-38 for flowering, roses stay balanced — not overfed, not starved — and bloom with lasting health and colour.

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How to Feed Roses for Strong Growth and Repeat Blooming

Roses respond best to small, regular feeds rather than heavy doses. A consistent routine keeps the soil active and roots continuously supplied with nutrients. Always water thoroughly before and after fertilising to protect delicate feeder roots.

Spring – Building Strength

Begin feeding when new shoots appear. Apply 20-20-20 every three to four weeks to promote strong leaf growth and sturdy canes capable of supporting heavy blooms.

Summer – Boosting Blooms

Switch to 4-18-38 + CaMg to enhance flower colour, fragrance, and longevity. Feed lightly every three weeks and water deeply to help nutrients reach the root zone.

Autumn – Storing Energy

Apply a light feed of 4-18-38 once monthly to help the plant store carbohydrates and prepare for winter dormancy. Avoid heavy nitrogen feeds late in the season.

Winter – Rest and Recovery

Pause fertilising after pruning. Resume feeding in early spring as soon as new growth emerges. Use mulch to protect roots and maintain steady moisture levels.

Potted roses need more frequent but diluted feeding — apply half-strength liquid every two to three weeks, flushing the pot monthly with fresh water to prevent salt build-up.

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Common Rose Feeding Questions

Why are my rose leaves turning yellow?
Usually from magnesium or nitrogen deficiency. Feed with 4-18-38 + CaMg to restore leaf colour and support new growth within two weeks.

How often should I fertilise roses?
Every three to four weeks through spring and summer. Frequent light feeding maintains healthy soil activity and constant bud development.

Can I use lawn fertiliser on roses?
Avoid it — lawn blends are high in urea and nitrogen, which cause soft, leaf-heavy growth. Use balanced NPK formulas like 20-20-20 or 4-18-38 for steady performance.

How can I encourage more blooms?
Regular feeding, light pruning, and deadheading spent flowers redirect energy to new buds. Potassium-rich fertilisers like 4-18-38 improve both quantity and quality of blooms.

Final Recommendation

For continuous flowering and vibrant colour, feed roses with
CompleteGrow All Purpose NPK 20-20-20 during active growth
and
Advanced NPK 4-18-38 + Calcium & Magnesium
through bloom cycles. This combination provides the full nutrient spectrum roses need — from firm stems to full, richly coloured flowers — keeping your garden blooming for months on end.