What Is a Good Fertilizer for Grapes?

A good fertilizer for grapes provides a balanced supply of nutrients that support both strong vine growth and the development of sweet, flavourful fruit. In Australia, the most effective approach is to begin with
CompleteGrow NPK 20-20-20 during spring growth, then switch to
CompleteGrow NPK 4-18-38 + CaMg through summer and autumn to maximise fruit set, sugar levels, and berry quality.

Nutritional Demands of Grapevines

Grapes are perennial crops that draw heavily on soil reserves. Unlike annual vegetables, they must maintain a woody framework, grow new canes each year, and ripen multiple clusters simultaneously. This requires consistent inputs of major nutrients:

Nitrogen (N): Essential for vigorous shoot and leaf growth. Too little leads to pale leaves and weak vines, while too much causes excessive foliage with poor fruiting.
Phosphorus (P): Fuels root expansion and flower initiation. Without it, grape clusters form poorly.
Potassium (K): Directly influences grape sweetness, colour, and berry size. Grapes are particularly heavy users of potassium.
Calcium & Magnesium: Critical secondary nutrients. Calcium improves skin firmness and prevents splitting, while magnesium prevents interveinal yellowing.

Because Australian soils are often sandy, alkaline, or leached by summer rain, they rarely supply this balance naturally. That’s why fertilizing is essential for consistent yields and fruit quality.

552747173_18321880465209903_5279276504497983881_n (1)

501220292_18349394419153754_6663243350617325120_n (1)

Seasonal Fertilizer Guide for Grapevines

The best fertilizer schedule aligns with the natural rhythm of the vine. Grapes progress through four key stages, and each stage requires a different nutrient focus:

Spring (September–November): As buds burst and shoots lengthen, nitrogen is vital for canopy growth. Apply
NPK 20-20-20 every 3–4 weeks to fuel both leaf expansion and root strength. This ensures vines establish the leafy “solar panels” needed to ripen fruit later in the season.
Summer (December–February): When grapes transition from flowers to forming clusters, potassium becomes the key nutrient. Switch to
NPK 4-18-38 + CaMg. High potassium drives sugar production, while calcium strengthens fruit skins, reducing splitting during hot weather.
Autumn (March–April): Grapes ripen and vines prepare for dormancy. A final light feed with 4-18-38 + CaMg helps vines finish fruiting strongly and store nutrients for the next season.
Winter (May–August): Grapevines are dormant. Fertilizing is unnecessary, but this is the time for pruning, mulching, and soil improvement.

Application Methods

Drip line feeding: Spread fertilizer around the outer edge of the canopy, where active feeder roots lie.
Deep watering: Always irrigate thoroughly after application to wash nutrients into the soil and reduce salt stress.
Container grapes: Use half-strength solutions more often (every 2–3 weeks), as pots lose nutrients rapidly.
Foliar feeding: In cases of visible deficiency, a diluted foliar spray provides a quick corrective boost.

552179083_18321880489209903_8856767690907421758_n (1)

551213638_18080765633493067_3849209301447550873_n

Fertilizer Mistakes to Avoid

Overloading with nitrogen: Encourages leaf growth at the expense of fruit. Always use balanced blends, not lawn fertilizer.
Fertilizing dry roots: Can cause burn and leaf tip damage. Always water first, then feed.
Feeding during dormancy: Wastes nutrients and may harm vines. Stop applications in winter.
Ignoring secondary nutrients: Calcium and magnesium are vital for fruit firmness and leaf health, especially in sandy soils.

FAQs: Good Fertilizer for Grapes

What is a good fertilizer for grapes? A two-step program: NPK 20-20-20 in spring, then NPK 4-18-38 + CaMg during summer and autumn.

How often should grapevines be fertilized? Every 3–4 weeks in the growing season. Container-grown grapes need smaller, more frequent feeds.

Do grapevines in pots need different care? Yes. Because nutrients leach out quickly, potted grapes benefit from diluted liquid feeds and occasional flushing with plain water to prevent salt build-up.

Can compost replace fertilizer? No. Compost improves soil structure but does not supply enough phosphorus, potassium, or secondary nutrients. Grapes require a complete NPK fertilizer program for reliable results.

By combining balanced spring feeding with NPK 20-20-20 and targeted summer fruiting support from NPK 4-18-38 + CaMg, grapevines can reach their full potential, producing strong canopies and heavy bunches of sweet, market-quality grapes year after year.