Best Liquid Fertilizer for Petunias: How to Feed for Endless Colour

Petunias are heavy-feeding annuals that bloom continuously through warm weather. To maintain their vibrant colour and constant flowers, they require consistent fertilizing—especially when grown in pots or hanging baskets where nutrients wash away quickly. The best liquid fertilizer provides instant nutrition and supports balanced growth without overfeeding.

Why Liquid Fertilizer Works Best

Petunias absorb nutrients most effectively in liquid form. Unlike slow-release granules that take weeks to dissolve, liquid fertilizers deliver nutrients directly to the root zone within hours. This rapid uptake helps recover colour, encourage more buds, and maintain strong stems even in hot or windy conditions.

What Petunias Need in a Fertilizer

Nitrogen (N): Keeps foliage green and fuels new shoot growth.
Phosphorus (P): Builds strong roots and supports continuous flowering.
Potassium (K): Enhances bloom size, colour intensity, and disease resistance.
Micronutrients (Fe, Mg, Zn): Maintain leaf colour and prevent yellowing (chlorosis).

A balanced NPK formula, such as 20-20-20, provides all these nutrients in equal measure for both growth and flowering phases.

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

For outdoor containers, garden beds, and hanging baskets, the CompleteGrow All Purpose 20-20-20 Liquid Fertilizer delivers professional-grade performance. It provides the same fast-acting, balanced nutrients as top commercial brands like Jack’s Fertilizer—without the synthetic fillers or harsh residues.

Instant uptake: Water-soluble for quick results and rapid greening.
Equal NPK balance (20-20-20): Maintains compact, flowering growth all season.
Micronutrients added: Iron, zinc, and magnesium prevent yellow leaves and dull colour.
Perfect for hanging baskets: Replenishes nutrients lost through frequent watering.

Dilute 5 mL per litre of water and apply every two weeks during the main growing season. For hanging baskets or planters, feed weekly at half strength. This consistent feeding schedule keeps petunias lush, colourful, and continuously blooming through late summer.

2. CompleteGrow Indoor Plant Food Concentrate

For verandas, balconies, and shaded indoor displays, the gentle
CompleteGrow Indoor Plant Food Concentrate
is the ideal fertilizer for petunias grown in decorative pots. Its mild, controlled formula nourishes roots without causing stretch or soft foliage.

Low phosphorus protects roots in smaller pots and compact soil.
Contains chelated micronutrients for steady leaf colour in lower light.
Perfect for petunias near windows, patios, or semi-shaded conditions.

Feed every 3–4 weeks according to label dilution. Indoor Plant Food provides lasting health and colour where heavier fertilizers might stress roots.

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How to Fertilize Petunias for Maximum Blooms

Water thoroughly before fertilizing to protect roots from burn.
Mix fertilizer according to instructions (5 mL per litre for 20-20-20, follow label for Indoor Food).
Apply evenly over the soil surface until just moist—avoid foliage contact.
Repeat fortnightly outdoors or monthly indoors during active growth.
Reduce feeding in winter or when plants stop flowering.

Frequently Asked Questions

Do petunias need fertilizer?
Yes. Without regular feeding, petunias lose colour and flower size quickly. Liquid fertilizer every two weeks maintains healthy growth and non-stop blooms.

Can I use Jack’s Fertilizer for petunias?
Jack’s is balanced, but CompleteGrow 20-20-20 Liquid Fertilizer offers the same professional performance locally—formulated for Australian water and soil conditions with cleaner micronutrient chelation.

What fertilizer is best for hanging basket petunias?
A balanced liquid like CompleteGrow 20-20-20 replenishes nutrients lost from daily watering and keeps flowers abundant all season.

Can I alternate fertilizers?
Yes—use 20-20-20 outdoors and switch to Indoor Plant Food for shaded or indoor pots to prevent overstimulation.

Final Recommendation

For the best results, fertilize petunias regularly with CompleteGrow All Purpose 20-20-20 Liquid Fertilizer for outdoor and hanging displays, and use CompleteGrow Indoor Plant Food Concentrate for shaded or indoor arrangements. Together, these products outperform generic options like Jack’s Fertilizer—providing Australian gardeners with balanced, fast-acting nutrition that keeps petunias healthy, compact, and covered in vivid blooms all season long.