Best Fertilizer for Soursop Trees – Complete Australian Guide

Soursop (Annona muricata), also known as Graviola or Guanabana, is a unique tropical fruit tree that produces large, spiny green fruits with soft, creamy white flesh. Renowned for its sweet-sour flavour and health benefits, it is a rewarding tree for Australian gardeners in warm, frost-free regions.

The soursop tree is a small to medium evergreen that can grow 4–6 metres tall under ideal conditions. It prefers full sun, protection from strong winds, and soil that drains well but retains moisture. Its dark green leaves and dramatic spiky fruits make it both an ornamental and productive feature in tropical and subtropical gardens.

Plant soursop trees in nutrient-rich, well-draining soil and keep the root zone consistently moist, especially in hot months. Mulch with organic matter to regulate soil temperature and preserve moisture, but keep mulch slightly away from the trunk to prevent rot. In Australia, fruiting typically occurs from late summer into autumn, with flowers and fruits forming directly on the trunk and mature branches. This fruiting habit makes consistent feeding crucial, as nutrient demand spikes during flowering and fruit development.

Patience is key with soursop trees. Seed-grown trees may take 3–5 years to fruit, while grafted trees fruit faster. Prune lightly after each harvest to remove dead wood and encourage new growth, which will help increase future yields. Avoid heavy pruning as the tree produces fruit on older wood.

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How to Fertilize and Care for Soursop Trees

Soursop trees are heavy feeders during their active growing and fruiting seasons. Proper fertilisation directly impacts fruit size, sweetness, and overall tree health. In Australia, start fertilising in early spring as the weather warms and continue through summer and early autumn. Reduce or stop fertilising during the cooler months when growth slows naturally.

Focus on providing a balanced nutrient profile. Young trees benefit from slightly more nitrogen to establish leafy growth and strong roots, while mature fruiting trees require higher potassium levels to encourage heavy flowering and improve fruit development. Fertilising every 4–6 weeks during the warm season ensures the tree never runs out of essential nutrients.

Alongside fertilisation, proper watering is critical. Soursop trees are sensitive to drought stress, which can cause flowers to drop and reduce fruit size. Keep the soil consistently moist but not waterlogged. In hot regions, morning deep watering helps maintain hydration throughout the day. Mulching with bark chips or sugarcane mulch will further support moisture retention.

Pruning is best done after fruiting has finished. Remove weak or crossing branches to improve airflow, which reduces the risk of fungal disease. Protect young trees from cold snaps or frost with covers or temporary shelters, as soursop is highly sensitive to cold damage.

Choosing the Best Fertiliser for Soursop Trees

For Australian growers seeking vigorous growth and reliable fruiting, a complete water-soluble fertiliser like CompleteGrow All Purpose NPK 20-20-20 is ideal. Its balanced formula provides nitrogen for healthy leaves, phosphorus for strong root systems and flowering, and potassium to boost fruit production and sweetness. Apply every 4–6 weeks during the growing season, adjusting rates as the tree matures.

Frequently Asked Questions

When should I fertilize my soursop tree? – Start in early spring and continue until late autumn, pausing in winter when growth slows.
Why isn’t my soursop tree fruiting? – Trees need 3–5 years to mature, and inadequate potassium or water stress can prevent fruiting.
Do I need to prune my soursop tree? – Light pruning after harvest improves airflow and encourages new fruiting wood.
How often should I water my soursop tree? – Keep the soil evenly moist; drought stress can cause flowers to drop and reduce fruit yield.

By combining deep watering, seasonal pruning, and a reliable NPK 20-20-20 feeding schedule, your soursop tree will thrive in Australian conditions and produce healthy, sweet fruits for years to come.