Blood Orange Fertiliser Guide: Feeding Schedule, NPK Ratios & Soil Prep

Blood orange trees are highly rewarding but nutrient-sensitive citrus that require a consistent, well-balanced fertiliser program to produce richly pigmented, sweet fruit. Whether you’re growing in a backyard, orchard, or large pot, correct nutrition at every growth stage directly impacts tree health, flowering, fruit quality, and colour intensity.

Why Feeding Matters for Blood Oranges

Blood oranges (Citrus sinensis var. sanguinea) develop their vibrant red internal colour through anthocyanin pigments, which are influenced not only by cool temperatures but also by potassium availability and overall plant health. A deficiency in nutrients—especially potassium, magnesium, or iron—can lead to small fruit, pale skin, or weak pigment formation.

This guide covers:

How to adjust NPK ratios across each phase of growth
Soil preparation techniques for citrus in Australian conditions
Feeding schedules for both in-ground and potted trees
The most effective CompleteGrow fertilisers for blood oranges

Improper fertilisation can lead to:

Pale or yellowing leaves (nutrient deficiencies such as nitrogen, iron, or zinc)
Poor blossom retention and fruit set
Dry, underdeveloped, or poorly coloured fruit
Reduced canopy growth and poor structural development

With proper feeding, blood orange trees grow vigorous canopies, produce fragrant blossoms, and bear heavy crops of flavour-rich fruit with deep internal colour.

Optimal NPK Ratios for Each Growth Stage

Nitrogen (N), Phosphorus (P), and Potassium (K) requirements change as citrus trees progress through growth, flowering, and fruiting. A staged fertiliser strategy is crucial for productive and healthy blood orange trees.

Young Trees (0–2 Years)

Objective: Establish strong roots, foliage, and canopy structure.
Recommended Product: CompleteGrow All Purpose Liquid NPK 20-20-20
Application: Apply monthly during spring and summer. This promotes rapid, even vegetative development while supporting root establishment.

Pre-Flowering and Bud Development (Late Winter to Early Spring)

Objective: Promote flower initiation and prevent premature bud drop.
Recommended Product: Use Cal-Mag Nutrient alongside 20-20-20.
Application: Apply weekly from late August through September to support cell wall strength and nutrient transport during new flushes.

Fruit Set and Maturation (Spring to Late Summer)

Objective: Enhance fruit retention, sweetness, juice volume, and red pigmentation.
Recommended Product: CompleteGrow NPK 4-18-38 + CaMg
Application: Begin in October after fruit set and continue through to late February. Apply every 3 weeks. The high potassium boosts sugar transport and anthocyanin production while phosphorus supports reproductive growth.

Micronutrients

Deficiencies in iron, zinc, or manganese can severely impact citrus leaf and fruit health, especially in alkaline soils. All CompleteGrow fertilisers include essential trace elements, but foliar sprays may be necessary if symptoms like interveinal chlorosis appear.

Annual Fertiliser Calendar, Soil Preparation and Growing Tips

Annual Feeding Guide (Australian Climate)

August: Light feed with NPK 20-20-20 to stimulate spring flushing
September: Begin Cal-Mag applications to prepare for blossom set
October–November: Alternate 20-20-20 and 4-18-38 as flowering transitions to fruiting
December–February: Focus on 4-18-38 + CaMg every 3 weeks to maintain fruit development and improve sugar levels
March: Final feed with high-potassium fertiliser to finish ripening and prepare for winter
April–July: No fertilising; allow the tree to rest. Maintain soil moisture and mulch.

Soil Preparation and Amendment

Ideal pH: 5.5 to 6.5. Citrus performs poorly in alkaline soils. Use a soil test annually.
Soil Type: Free-draining, loamy soils are best. Avoid clay or compacted soil.
Improvement Tips: Blend in pine bark fines and perlite to improve porosity and drainage. Avoid composts or animal manures if you’re strictly using chemical fertilisers.
Mulch: Apply coarse mulch 5–10 cm thick around the root zone, leaving a gap at the trunk to prevent rot.

Pot-Grown Blood Oranges

Container Size: Minimum 40–50 cm diameter for mature trees
Feeding Frequency: Every 2–3 weeks with diluted CompleteGrow 20-20-20 or 4-18-38 depending on season
Drainage: Ensure pot has several large holes and never allow water to pool at the base
Leaching: Every 3–4 months, flush the soil with clean water to remove salt buildup from fertilisers

Application Guidelines

Apply fertilisers to moist soil only—never to dry ground
Use a watering can or pressure sprayer for even application
Water in thoroughly after feeding to move nutrients into the root zone
Avoid applying fertiliser directly at the trunk; instead, spread around the dripline

By following this professional feeding strategy and using targeted CompleteGrow nutrient products, you’ll encourage steady growth, robust flowering, and premium fruit quality season after season—bringing out the very best your blood orange tree has to offer.