The Grain Harvest Cycle: Why Wheat and Soybean Prices Are Predictable

Grain prices follow the harvest cycle with a consistency that has made agricultural commodity trading one of the oldest forms of seasonal investing. The fundamental driver is simple: before harvest, supply is uncertain and prices carry a weather premium. After harvest, supply is known and prices fall under the weight of new crop availability.

The Pre-Planting Premium

The most reliable seasonal window for grain prices is the period from October through April — the pre-planting and growing season. During this window, the market is pricing in uncertainty about the coming crop. Will there be enough rain? Will there be a late frost? Will planting be delayed? These questions cannot be answered until the crop is in the ground and growing, and the market compensates for this uncertainty by maintaining a premium in futures prices.

For wheat, the pre-planting premium is particularly pronounced because winter wheat is planted in September–October and harvested in June–July. The entire growing season — from planting through harvest — is a period of supply uncertainty, and prices typically reflect this with a sustained upward bias from October through May.

For soybeans, the growing season runs from May through September, with harvest in September–October. The pre-planting premium builds from October through April as the market anticipates the coming planting season. The critical weather window — when soybean pod fill occurs and prices are most sensitive to weather forecasts — is July and August.

Harvest Pressure: The Seasonal Sell Window

Once harvest begins, the supply uncertainty that supported prices is resolved. Farmers sell grain to pay for harvest expenses and service debt. Elevators and storage facilities fill rapidly. Basis levels — the difference between local cash prices and futures prices — typically weaken sharply as local supply overwhelms local demand.

For corn and soybeans, the harvest pressure window runs from September through November. For wheat, it runs from June through August. During these windows, prices historically face their strongest seasonal headwinds, and the average monthly returns are consistently negative.

The Corn Seasonal Pattern

Corn is the largest crop by volume in the United States and has one of the most well-documented seasonal patterns in agricultural markets. The seasonal cycle is driven by the planting-to-harvest calendar, with a secondary influence from the ethanol demand cycle (which is relatively stable year-round) and the livestock feed demand cycle (which peaks in winter).

Corn prices historically bottom in October–November at harvest, then rally through the winter and spring as the market prices in the coming planting season and winter feed demand. The seasonal peak typically occurs in June–July, when weather risk for the current crop is at its maximum. After the crop is made in August, prices typically decline through harvest.

The Soybean-Corn Ratio

An important nuance in grain seasonality is the relationship between soybean and corn prices. Farmers make planting decisions based on the relative profitability of the two crops, which is captured by the soybean-to-corn price ratio. When soybeans are relatively expensive compared to corn, farmers plant more soybeans and fewer corn acres, and vice versa. This dynamic creates a secondary seasonal influence on both markets as the planting intentions report (released by the USDA in late March) approaches.

Historical Seasonal Performance

Month	Wheat Signal	Soybeans Signal	Corn Signal
January	BUY	BUY	BUY
February	BUY	BUY	BUY
March	BUY	BUY	ACCUM
April	BUY	BUY	ACCUM
May	BUY	ACCUM	NEUT
June	SELL	NEUT	NEUT
July	SELL	NEUT	SELL
August	SELL	SELL	SELL
September	NEUT	SELL	SELL
October	ACCUM	ACCUM	ACCUM
November	BUY	BUY	BUY
December	BUY	BUY	BUY

The full interactive grain seasonal calendar — with monthly signals, average returns, and source citations — is available free at comcalend.com. Supported by Walmer Portal.