Best Fertiliser for Petunias: Feed for Vibrant Colour & Long Blooming

Petunias are fast-growing annuals that bloom heavily for months—but only when their nutrient balance stays consistent. Because they flower almost continuously, petunias are among the hungriest container plants you can grow. A steady feeding program using a balanced liquid fertiliser is essential for dense foliage, colourful blooms, and extended life in both pots and garden beds.

Why Balanced Fertilising Matters

Petunias use large amounts of nitrogen and potassium as they produce foliage and flowers simultaneously. Without regular feeding, leaves fade to pale green, flower size diminishes, and blooming slows dramatically. The best fertiliser for petunias maintains a near-equal NPK ratio—providing enough nitrogen for growth, phosphorus for strong roots, and potassium for prolific flowering.

Liquid Fertiliser vs Granular

Liquid fertilisers are ideal for petunias because nutrients reach roots instantly, encouraging faster recovery from heat and pruning stress. Granular fertilisers release too slowly to sustain consistent blooming, especially in pots. For the best results, choose a liquid solution you can apply every one to two weeks throughout the growing season.

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1. CompleteGrow All Purpose 20-20-20 Liquid Fertiliser

For outdoor containers and garden beds, CompleteGrow All Purpose 20-20-20 delivers professional-grade nutrition trusted by commercial growers. The balanced NPK ratio gives petunias everything they need for continuous, vibrant flowering.

20% Nitrogen (N): Fuels fast foliage recovery after pruning and maintains healthy green leaves.
20% Phosphorus (P): Encourages strong root development and nutrient absorption in warm soils.
20% Potassium (K): Drives larger, more colourful blooms and improves drought resistance.
Trace Elements: Added iron, magnesium, and zinc prevent leaf chlorosis and enhance pigment formation.

Mix 5 mL per litre of water and apply to moist soil every two weeks during active growth. In heavy bloom periods, feed weekly at half strength for uninterrupted colour. Regular feeding with 20-20-20 produces tighter growth, brighter petals, and stronger flowering stems.

2. CompleteGrow Indoor Plant Food Concentrate

For shaded patios, verandas, or indoor petunia displays, use the gentler CompleteGrow Indoor Plant Food Concentrate. Its low-strength formulation delivers steady, safe nutrition to maintain compact, controlled growth in smaller pots.

Low phosphorus content protects roots in confined containers.
Balanced nitrogen keeps foliage lush without excessive stretching.
Trace elements sustain healthy chlorophyll levels even in low-light conditions.

Apply every three to four weeks by diluting according to label instructions. It’s perfect for decorative pots or indoor planters where standard fertilisers may cause overfeeding or leaf burn.

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Petunia Feeding Schedule

Spring: Start weekly light feeding once seedlings are established.
Summer: Feed fortnightly with 20-20-20; water thoroughly after application.
Autumn: Continue monthly to sustain flowering until cool weather.
Winter (warm zones): Use Indoor Plant Food sparingly for overwintered pots in bright light.

Frequently Asked Questions

Can I use any fertiliser on petunias?
Avoid lawn or rose fertilisers—they’re too strong in phosphorus. Petunias prefer a balanced, water-soluble product like 20-20-20.

How often should I feed petunias in hanging baskets?
Because water drains quickly, feed weekly at half strength using 20-20-20 or every 3–4 weeks with Indoor Plant Food for shaded baskets.

Can I mix Indoor Plant Food and 20-20-20?
Use one or the other depending on location. Outdoor plants thrive on 20-20-20, while shaded or indoor pots respond best to Indoor Plant Food.

What happens if I over-fertilise?
Excess nutrients cause leaf burn and reduce flowering. Always dilute according to directions and water well after feeding.

Final Recommendation

For brilliant colour and long-lasting blooms, feed petunias consistently with CompleteGrow All Purpose 20-20-20 Liquid Fertiliser for outdoor growth and CompleteGrow Indoor Plant Food Concentrate for shaded or indoor containers. Both deliver professional-grade results—balancing growth, bloom production, and root health—ensuring petunias remain compact, lush, and flowering right through the warm months.