Rhubarb Fertiliser Guide: Varieties, Soil Prep, NPK Ratios & Feeding Schedule

Rhubarb is a nutrient-demanding, long-lived perennial vegetable prized for its tart, fleshy stalks and reliable seasonal yields. Native to cold climates, it thrives in temperate parts of Australia with rich soil and proper fertilisation.

About the Plant: Growth Habits & Lifecycle

Botanically classified as Rheum rhabarbarum, rhubarb is a herbaceous perennial that forms large underground crowns. Thick petioles (leaf stalks) grow from these crowns and are harvested for culinary use. The plant enters dormancy in winter and re-emerges in late winter to early spring as temperatures rise.

Unlike annual vegetables, rhubarb requires long-term soil fertility and root system development. Plants typically reach full maturity in 2–3 years and can remain productive for 10–15 years with proper care. Only the stalks are edible—rhubarb leaves contain oxalic acid and should never be consumed.

Rhubarb Varieties Grown in Australia

Ever Red: A reliable variety widely grown in Australia. Produces deep red, thick stalks and is well suited to both home gardens and market gardens.
Sydney Crimson: Common in NSW and southern Queensland. Known for consistent colour, good flavour, and heat tolerance. Often used in commercial production.
Victoria: An older green-stalked variety with red blushing. Grows vigorously and tolerates heat but may lack full red pigmentation. Used historically in cooler regions like Tasmania and Victoria.
Wandin Red: A newer cultivar bred in Victoria. Very uniform and rich in colour. Excellent for consistent quality and flavour.

In Australia, rhubarb grows best in temperate regions such as Victoria, southern NSW, South Australia, Tasmania, and cooler parts of WA. It can be grown successfully in parts of Queensland if given some shade and sufficient water during hot summers.

Ideal Conditions for Rhubarb in Australia

Climate: Cool to mild climates with cold winters and moderate summers are ideal. Requires winter chill to break dormancy effectively.
Soil: Rich, well-drained, loamy soil with high organic matter. Slightly acidic to neutral pH (6.0–6.8) is ideal.
Position: Full sun is preferred in cooler climates. In hotter regions, light afternoon shade may reduce summer stress.
Watering: Rhubarb requires consistent moisture. Dry periods can cause stalks to become woody or bitter.

Because rhubarb is a deep feeder with a long growing season, fertiliser application is critical not only at the start of spring but throughout the growing cycle. Proper nutrition results in thicker, better-coloured stalks and longer harvest windows.

NPK Ratios for Rhubarb Growth Phases & CompleteGrow Product Strategy

Rhubarb’s nutritional needs change over the course of its lifecycle. Young plants require a strong nitrogen base to promote leaf and root growth, while mature plants need added potassium to support flavour and stalk density.

Establishment Phase (Year 1)

Objective: Build a strong root system and crown without harvesting stalks.
Recommended Product: All Purpose Liquid Fertiliser NPK 20-20-20
Application: Apply every 4 weeks from early spring to late summer. This supports both below-ground and above-ground development.

Productive Phase (Years 2 and Beyond)

Spring to Early Summer: Continue feeding with NPK 20-20-20 every 3–4 weeks to support lush regrowth and early harvests.
Mid to Late Summer: Transition to NPK 4-18-38 + CaMg. The higher potassium level promotes thicker stalks, improved red pigmentation, and stronger structural tissues.
Optional Micronutrient Support: Apply Cal-Mag monthly to prevent leaf tip burn or interveinal chlorosis, especially in sandy or acidic soils.

Signs of Nutrient Deficiency

Thin or spindly stalks: May indicate lack of nitrogen or general underfeeding
Discoloured leaves or leaf tips: Can result from magnesium or calcium deficiency
Low red colour in stalks: Often due to poor potassium levels or excess heat

By feeding with CompleteGrow’s premium liquid and powder fertilisers, you can maintain consistent growth and extend your harvest window without stalks becoming bitter or stringy.

Feeding Calendar, Soil Tips & Rhubarb Management

Annual Fertilising Calendar

August: First application of NPK 20-20-20 as buds begin to swell
September–November: Feed monthly with 20-20-20 or alternate with Cal-Mag if foliage appears pale
December–February: Switch to NPK 4-18-38 + CaMg to improve stalk texture and flavour during heat
March: Apply one final round of potassium-rich fertiliser
April–July: Stop feeding. Allow plant to rest through winter. Remove old leaves and mulch crowns for frost protection.

Soil Improvement & Crown Maintenance

Soil Drainage: Ensure raised beds or mounded rows to prevent root rot
pH Range: 6.0–6.8 is optimal. Apply lime if soil is too acidic
Mulch: Use coarse mulch (bark, straw) to conserve moisture and prevent weed competition
Crown Division: Every 4–5 years, divide rhubarb crowns in late winter to refresh productivity

Container Growing Considerations

Use large containers (50L or larger) with premium potting mix
Feed more frequently (every 2–3 weeks) due to nutrient leaching
Provide partial shade in hot regions to avoid bolting or dormancy

With a consistent feeding plan, soil awareness, and CompleteGrow’s high-quality fertilisers, your rhubarb plants can provide reliable harvests for over a decade—resulting in thick, juicy stalks perfect for pies, preserves, or fresh use.