Why Potatoes Are Small at Harvest

Harvesting potatoes only to find they are small can be disappointing, but it’s a common issue with clear causes. Small potatoes usually result from stress during growth, poor growing conditions, or harvesting too early. Understanding the reasons helps you avoid the problem in future seasons and improve yields.

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• Seed Potato Collection (Early, First & Second Earlies)
A mixed pack of quality seed potatoes to plant for a steady harvest from early summer through to autumn. Ideal if you want variety in size and maturity times.
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• Potato Grow Bags / Containers
Reusable, breathable bags designed specifically for growing potatoes — great for patios, small gardens, or increasing yield in limited space.
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• Potato Fertiliser / Soil Booster
Specially formulated feed to support healthy tuber development and improve yields — apply at planting or as a top-dress during the season.
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• Potato Planting Guides & Markers
Helpful tools and guides that take you through planting depth, spacing, and care — plus reusable markers to keep track of different varieties.
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Harvesting Too Early

One of the most common reasons for small potatoes is lifting them too soon. Potatoes bulk up towards the end of their growing period.

• Early harvesting limits tuber size
• Maincrop potatoes need time for skins to set and tubers to enlarge
• Even early potatoes benefit from an extra week or two if conditions are good

Patience often makes the biggest difference.

Poor Watering During Tuber Formation

Potatoes need consistent moisture when tubers are forming.

Problems include:

• Drought or missed watering
• Inconsistent watering patterns
• Dry soil followed by heavy watering

These conditions restrict tuber growth and result in many small potatoes.

Lack of Nutrients

Insufficient nutrients limit growth.

Common causes:

• Poor soil fertility
• Lack of organic matter
• Underfeeding in containers

Potatoes require balanced nutrition, especially potassium, to develop large, healthy tubers.

Overcrowding Plants

Planting potatoes too close together causes competition for water and nutrients.

Results include:

• More tubers but much smaller in size
• Reduced overall yield

Correct spacing helps tubers grow larger rather than numerous but tiny.

Too Much Nitrogen

Excess nitrogen causes leafy growth at the expense of tubers.

Signs include:

• Lush foliage
• Poor tuber development
• Lots of small potatoes

Balanced feeding is essential for good tuber size.

Poor Soil Structure

Compacted or stony soil physically restricts tuber growth.

Problems include:

• Misshapen potatoes
• Limited expansion space
• Shallow tuber development

Loose, stone-free soil allows tubers to grow properly.

Heat or Weather Stress

Hot, dry weather or sudden temperature changes stress plants.

Effects include:

• Slowed tuber development
• Reduced tuber size
• Premature growth shutdown

Mulching and consistent watering help reduce weather stress.

Disease or Pest Damage

Pests and disease reduce plant energy.

Common issues:

• Blight
• Slugs
• Wireworm
• Virus-infected plants

Stressed plants divert energy away from tuber growth.

Container Size Too Small

Growing potatoes in containers that are too small limits root and tuber development.

Shallow or narrow containers result in many small potatoes instead of fewer large ones.

Poor Earthing Up

Inadequate earthing up exposes tubers and limits growth.

Proper earthing up:

• Protects tubers
• Encourages deeper growth
• Supports better tuber size

Late Planting

Late-planted potatoes have less time to grow and bulk up, especially maincrop varieties. Shortened growing seasons often lead to smaller potatoes at harvest.

How to Prevent Small Potatoes Next Time

To improve potato size:

• Plant at correct spacing
• Water consistently, especially during flowering
• Feed with balanced nutrients
• Use large containers
• Improve soil structure
• Harvest at the right time

Healthy plants produce larger tubers.

Final Thoughts

Small potatoes at harvest are usually the result of early lifting, water stress, poor nutrition, or overcrowding. By focusing on soil quality, consistent care, and correct timing, you can significantly improve potato size and overall yields in future harvests.