Potato bulking stage: what to do in these 30 days

In the bulking month, keep soil evenly moist with light, frequent irrigation. Keep every tuber covered with soil. Protect leaves before cool, cloudy, humid weather brings late blight. Stop irrigation about 7 to 15 days before haulm cutting, longer on heavy soil. Avoid long dry gaps followed by heavy flooding.

Updated 2026-11-09

See also: Potato guide and Immunity Potato Special.

Tubers now grow in size and weight. Our potato guide puts this stage at about 8 weeks to harvest, and it varies by variety. A crop planted in mid October reaches it around December. The fertilizer schedule covers what to apply, and why potatoes stay small covers diagnosis. This page covers only the field work for the next 30 days.

Day 1: walk the field and fix your dates

• Dig a few plants from different parts of the field. See how many tubers are set and whether any are near the surface.
• Squeeze soil from tuber depth (see the test below).
• Write down your planned haulm cutting date. Your last irrigation is counted back from this date.

Days 1 to 20: keep the water even

ICAR-CPRI says the crop needs light and frequent irrigation, mainly on light soils. It also advises keeping available soil moisture at 65 to 85 percent during active growth. FAO reports that using more than 50 percent of the available soil water lowers yield, and that shortage early in yield formation increases spindle-shaped tubers.

How often depends on your system and region:

CPE is cumulative pan evaporation. Your nearest KVK or weather station can give the figure.

North Gujarat soils can be light. The trial soil at the SDAU station at Aseda was loamy sand. In one two-season trial at SDAU Sardarkrushinagar on a processing variety, drip with a lateral in each row gave more processing-grade tubers than perforated pipe, micro-sprinkler and furrow. In the Bikaner study, micro-sprinklers out-yielded drip. So results depend on place and system. Do not change your system mid-season. Run the one you have evenly.

Check moisture by hand. University of Minnesota gives these signs:

• Loamy sand, enough water: looks moist, makes a weak ball or slightly sticks together.
• Loamy sand, too dry: will not form a ball under pressure.
• Sandy loam, enough water: fairly dark, makes a good ball.
• Sandy loam, too dry: only lightly coloured, will not ball.
• Either soil, very wet: leaves a wet outline on your hand.

Too much water also harms. CPRI says excess moisture creates aeration problems and favours some diseases. Too much water combined with late heavy rain can raise post-harvest rot. NDSU links moisture stress to second growth and advises uniform moisture without overwatering. University of Minnesota links swings between too much and too little water to hollow heart. FAO also notes that frequent irrigation with cold water can cool soil below the 15 to 18°C it gives as best for tuber formation.

Earthing: repair, do not rebuild

CPRI's guidance for the plains is that hoeing, done with earthing up, should not go beyond 30 days after planting (45 days in the hills). So the main earthing should already be done. Practice varies: TNAU, writing for Tamil Nadu, advises earthing at 60 days to keep tuber moth off exposed tubers.

Now walk the ridges, especially after each irrigation. Where a ridge has cracked or washed, pull soil over the tuber by hand. Do not run a machine through a closed crop. Ohio State University warns that hilling after vines flop and begin to close rows can be damaging.

CPRI says light turns tubers green and builds up toxic glycoalkaloids. NDSU says never to eat tubers green beneath the skin, and to discard those with extensive greening.

All 30 days: blight and frost watch

CPRI says late blight spreads at 15 to 20°C with humidity above 80 percent. Its disease bulletin adds that cloudy weather favours it. That bulletin records first appearance in 2015-16 on 27 November at Modipuram, 8 December at Pantnagar, 12 December at Ludhiana and 30 January at Kalyani in West Bengal. Dates shift each year. We found no published date for Banaskantha, so watch the same weather signs and ask your KVK or the Potato and Sorghum Research Station at Deesa.

Look for water-soaked, pale green patches near leaf tips and edges, and brown marks circling stems. On tubers, look for reddish-brown to purple patches. CPRI says tubers get infected when rain or dew carries spores down from diseased leaves.

What to do:

• Do not wait for spots. CPRI advises a protective spray before the canopy closes, reaching the lower leaves too.
• If blight appears, CPRI advises changing to a different fungicide type. Follow the current recommendation of your state agricultural university or KVK for product and dose.
• CPRI's bulletin says to stop irrigation when weather turns favourable for blight. Keep this delay short, and restart when the weather clears.

Frost is the other risk in the north. A review on Punjab reports that below 1°C for more than 4 to 5 hours can cause 50 percent foliage loss in a night, and that damage is greater at 50 to 60 days after planting than at 80 to 90 days. The Bikaner study reports that micro-sprinklers protected the crop from low temperatures.

Last stretch: stop water, then cut haulms

Count back from haulm cutting, not from digging.

• CPRI's post-harvest guidance: stop irrigation at least one week before haulm cutting, so the skin cures and digging is easier.
• CPRI's seed crop guidance: about 10 days before in light soil and 15 days in heavy soil.
• Seed crop haulm killing dates from the same guidance: end of December for Punjab, Haryana and western UP; by 10 January for central UP and MP; by 15 January for eastern UP, Bihar, West Bengal and Odisha.

Those dates are for seed crops. A crop grown for eating may follow a different date. For Gujarat, confirm your date locally. CPRI advises harvesting 15 to 20 days after haulm killing, when the field is workable and the skin has hardened. Rub a tuber with your thumb: if the skin peels, it is not ready.

If blight has badly taken over, CPRI's bulletin says to cut haulms at 75 percent disease severity.

What to avoid

• A long dry gap followed by a heavy flood.
• Irrigating into cool, cloudy, humid weather.
• Late urea. CPRI notes excess nitrogen increases undesirable extra-large tubers.
• Leaving the crop in the ground too long after haulm killing. CPRI reports that late-harvested crops show more black scurf.
• Digging wet soil, which CPRI links to soft rot.

Where Immunity fits

Send us your variety, planting date, soil type, irrigation method and a photo of the crop, and we will suggest what to check next: +91 99787 91167 (call or WhatsApp) or sales@gujaratbio.com.

Sources

• Agro-techniques for quality seed potato production, Indian Farming 74(05), ICAR-CPRI
• Nutrient and water management for potato, Indian Farming 74(05), ICAR-CPRI
• Post-harvest management of potatoes, Indian Farming 74(05), ICAR-CPRI
• Disease management in seed potato production, Indian Farming, ICAR-CPRI
• Diseases and Pests of Potato and their Management, ICAR-CPRI Shimla
• FAO Land and Water: crop information, potato
• Potato Cultivation in Non-traditional Areas of Rajasthan, Indian Horticulture
• Effect of irrigation methods and split application of N and K on potato under North Gujarat conditions, Agricultural Science Digest
• Response of sources and levels of nitrogen on potato through drip fertigation, SDAU Aseda, Potato Journal 50(2)
• Effect of climate variability on potato yield in Punjab, Potato Journal 49(2)
• Potato Tuber Second Growth, NDSU Extension A1987
• Green potatoes, NDSU Extension
• Growing potatoes, University of Minnesota Extension
• Estimating soil moisture by feel and appearance, University of Minnesota Extension
• Optimize potato seeding depth and hill management, Ohio State University VegNet
• TNAU Agritech: Potato
• Agriculture Contingency Plan for District Banaskantha, ICAR

By Gafar Laiya, founder of Gujarat Bio Organics, working with farmers since 2006. Results differ from farm to farm with soil, weather, crop and management. Farmer experiences on this site are their own reports, not a promise of results.