Best Fertiliser for Sweet Potatoes: How to Grow Lush Vines & Bumper Crops

Sweet potatoes (Ipomoea batatas) are nutrient-rich root vegetables prized for their edible tubers and attractive, fast-spreading vines. With the right conditions and feeding, they grow vigorously and produce a high yield—whether in the ground or pots.

What Are Sweet Potatoes & How Do They Grow?

Unlike regular potatoes, sweet potatoes are not from the nightshade family. They’re actually a warm-season crop in the morning glory family, with heart-shaped leaves and sprawling vines that root wherever they touch the soil.

Botanical Name: Ipomoea batatas
Climate: Prefers warm to hot weather—ideal for Australian spring through late summer
Growth Period: 4 to 6 months from planting to harvest
Planting Method: Grown from ‘slips’—sprouts taken from a mature sweet potato

Sweet potatoes are grown primarily for their underground tubers. Once established, their vines spread rapidly, covering large areas and suppressing weeds. They thrive in sunny, well-drained spots and need plenty of nutrients to bulk up underground tubers while supporting healthy leaf production.

How to Plant & Care for Sweet Potatoes in Your Garden or Pots

Planting Sweet Potato Slips

Sweet potatoes are not grown from seeds—they’re grown from ‘slips’, which are vine cuttings or shoots grown from a mature sweet potato.

Cut slips when they reach 10–15 cm and remove lower leaves
Plant directly into warm soil, burying nodes 5 cm deep and spacing 30–40 cm apart
Water thoroughly after planting and keep soil consistently moist

Growing in the Ground

Soil Type: Loose, sandy or loamy soil with good drainage and a pH of 5.5 to 6.5
Bed Preparation: Mound up rows to improve drainage and prevent tuber rot
Sunlight: Full sun—at least 6 hours daily

Growing in Pots or Containers

Choose deep pots (at least 30–40 cm deep) with plenty of room for vines to trail
Use a lightweight potting mix enriched with a balanced liquid fertiliser
Water deeply once or twice a week—don’t allow soil to completely dry out

Maintenance & Common Problems

Overwatering: Can lead to root rot or fungal issues
Poor Tuber Growth: Usually due to poor soil fertility or excess nitrogen
Pest Issues: Monitor for caterpillars, weevils, or aphids on young foliage
Yellowing Leaves: May indicate magnesium deficiency or water stress

Sweet potatoes are hardy once established, but will benefit greatly from regular light feeding to support leaf growth and develop starchy, nutrient-rich tubers underground.

What’s the Best Fertiliser for Sweet Potatoes?

Sweet potatoes require a fertiliser that supports strong root development without overstimulating leafy growth. The wrong fertiliser—especially one with too much nitrogen—can result in lots of vine growth but small or underdeveloped tubers.

Ideal NPK for Sweet Potatoes

Low to Moderate Nitrogen (N): Encourages some leaf growth without sacrificing root size
Higher Phosphorus (P): Critical for root and tuber development
Moderate to High Potassium (K): Boosts overall plant resilience, flavour, and sugar content
Calcium & Magnesium: Improve cell wall strength and prevent tuber deformities

Feeding Schedule

At Planting: Use a liquid starter fertiliser with moderate phosphorus to encourage initial root development
2–4 Weeks After Planting: Switch to a high potassium formula to support tuber formation
Mid-Season: Reapply liquid fertiliser every 2–3 weeks until harvest
Final Month: Reduce feeding to allow sugars to accumulate in the tubers

Sweet potatoes grown in containers may need more frequent feeding due to nutrient leaching. Always feed when soil is moist and avoid applying during the hottest part of the day.

With the right balance of nutrients and consistent care, your sweet potato patch will reward you with large, tasty tubers ready to harvest around 16–20 weeks after planting.