Yellow Squash Turning Brown on Bottom: Blossom-End Rot Solutions

Diagnosing and Fixing Blossom-End Rot on Squash

When young yellow squash develop brown, soft spots on the blossom end and shrivel before harvest, it's classic blossom-end rot—usually caused by pollination failure or water management issues.

Two Primary Causes

1. Incomplete pollination: Fruit initiates but aborts without viable seeds.
2. Water fluctuation: Irregular moisture prevents calcium transport to developing fruit.

Pollination Fixes

• Hand-pollinate: Transfer pollen from male to female flowers (female has miniature fruit at base) using a brush or cotton swab.
• Do this within 1 day of female flower opening.
• Plant bee magnets: sunflowers, marigolds, cosmos, zinnias near squash beds.
• Avoid broad-spectrum insecticides during bloom.

Water Management

• Provide consistent 1.5 inches of water per week.
• Water deeply 1–2 times weekly, not lightly daily.
• Mulch heavily with straw or dried grass clippings to stabilize soil moisture.
• Check soil 2 inches down—water when dry at that depth.

Fertilizer Strategy

• Use low-nitrogen, high-phosphorus fertilizer every 2 weeks.
• Excess nitrogen promotes leaves over fruit and worsens calcium uptake.
• Look for tomato/vegetable formulations (e.g., 5-10-5 or similar).

Long-Term Soil Health

Amend beds annually with organic matter: compost, aged manure, shredded leaves, peat moss. This improves drainage, nutrient retention, and microbial activity—reducing both water stress and disease pressure. Well-amended soil grows healthier, more productive crops with fewer problems.

Address both pollination and water consistency for full-sized, blemish-free squash harvests.