Best Fertilizer for Squash Plants: Growth & Feeding Guide for Australian Gardens

Squash plants, including zucchini, butternut squash, and button squash, are productive and rewarding additions to the home garden. With their large, heart-shaped leaves, vigorous vines, and bright yellow flowers, these members of the Cucurbita family can produce abundant harvests in just one season. Feeding squash plants properly is essential to support their rapid growth and fruiting, and using the best fertilizer ensures strong vines, healthy leaves, and plentiful squash throughout the season.

Squash plants are warm-season growers that thrive in full sun and nutrient-rich soil. In Australia, planting times vary by region, but most gardeners sow seeds or seedlings in spring and early summer when the risk of frost has passed. Common varieties include:

Zucchini (Cucurbita pepo): Fast-growing with cylindrical fruits; perfect for continuous summer harvests.
Butternut squash (Cucurbita moschata): A trailing variety with sweet, nutty-flavoured fruits and long storage potential.
Button squash (Scallopini): Small, tender, saucer-shaped fruits; ideal for quick harvests and stir-fries.
Spaghetti squash: Unique fruits that produce stringy, pasta-like flesh after cooking.

Healthy squash plants require consistent watering, a sunny position, and soil enriched with organic matter or composted material. However, these fast growers are heavy feeders, quickly exhausting nutrients in the soil. Without the right fertiliser, you may notice yellowing leaves, fewer flowers, or reduced fruiting.

Companion planting can also support vigorous growth. Marigolds and nasturtiums deter pests, while beans fix nitrogen in the soil, helping feed nutrient-hungry squash vines naturally. Knowing your plant’s growth pattern is the first step before introducing a proper feeding schedule.

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Understanding Squash Plant Fertiliser Needs

Squash plants have three key growth stages—vegetative growth, flowering, and fruit production—each requiring slightly different nutrient support. A well-timed feeding plan will keep leaves lush, flowers abundant, and fruit production steady.

1. Early Growth (Seedling to 4 Weeks): Seedlings benefit from a balanced fertiliser with slightly higher nitrogen to encourage rapid leaf and stem growth. Yellowing or slow development at this stage often indicates a nitrogen deficiency.

2. Flowering & Fruit Set (5–8 Weeks): Once the first male and female flowers appear, the plant shifts its energy to reproduction. Excess nitrogen at this stage may cause excessive leafy growth at the expense of flowers and fruit. Switching to a fertiliser higher in potassium and phosphorus will encourage more flowers and better fruiting.

3. Peak Harvest Stage (9 Weeks+): Continue feeding every 2–3 weeks with a balanced formula to sustain fruit production. Keep soil consistently moist but avoid waterlogging, which can cause root rot or blossom end rot in fruiting squash.

Common nutrient deficiencies in squash include magnesium (yellowing between veins on older leaves) and calcium (blossom-end rot). A fertiliser plan that includes these essential trace elements helps prevent common problems before they appear.

Feeding Schedule Tip: Apply fertiliser after watering to reduce the risk of root burn. Mulching with straw or sugarcane mulch helps retain moisture and moderates soil temperature for optimal nutrient uptake.

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Best Fertiliser for Squash Plants & Common Questions

For vigorous squash plants and abundant harvests, a complete fertiliser that supplies balanced NPK and essential micronutrients is ideal. We recommend using CompleteGrow’s All Purpose Plant Liquid Fertiliser (NPK 20-20-20) at half strength during early growth, then transitioning to full-strength applications every 2–3 weeks during flowering and fruiting. This formula delivers the right balance of nitrogen for leaf growth, phosphorus for strong root and flower development, and potassium for consistent fruiting.

Frequently Asked Questions

1. How often should I fertilise squash plants?
Feed every 2–3 weeks during the growing season, increasing frequency during peak fruiting for sustained harvests.

2. Should I fertilise potted squash plants differently?
Yes. Container-grown squash require more frequent feeding as nutrients leach out with watering. Apply a diluted liquid feed every 1–2 weeks.

3. Can over-fertilising harm squash plants?
Excess nitrogen can lead to leafy growth with few fruits. Always follow recommended dilution rates to avoid nutrient burn and poor yields.

4. Do squash plants need additional calcium or magnesium?
Yes. Supplemental calcium and magnesium can prevent blossom end rot and leaf yellowing, especially in sandy or low-fertility soils.

By following a consistent feeding routine and using a complete, balanced fertiliser, you’ll enjoy healthy vines and a continuous supply of fresh squash from your garden.