Canola is a globally significant oilseed crop derived from rapeseed. Determining the correct time to harvest directly impacts the final yield and commercial quality of the seed. Unlike many other crops, canola is an indeterminate plant, meaning its flowers and pods develop continually, resulting in uneven maturity across a single plant. The precise harvest window is influenced by the specific variety planted, the geographic climate, and the plant’s physical readiness.
Spring vs. Winter Varieties: The Core Timing Difference
The primary factor dictating the general harvest season for canola is whether a spring or winter variety is grown. Spring canola is the dominant type in cooler climates, such as the northern Great Plains of the United States and the Canadian Prairies. This variety is planted in the early spring and is harvested in the late summer, typically spanning from late August into early September.
Winter canola is planted in the fall, about six weeks before the first killing frost, allowing it to establish a strong root system before going dormant for the winter. After surviving the cold months, it resumes growth in the spring and is harvested much earlier in the year, commonly in June or early July. The benefit of the winter variety is its extended growing period, which often results in a higher yield potential.
Indicators of Optimal Harvest Readiness
The decision to initiate harvest relies on specific biological and physical indicators that signal the crop has reached physiological maturity. The most fundamental sign is the change in the seed’s color, which must transition from a translucent, watery-green to a firm, mature color such as light yellow, reddish-brown, or black. This color change is crucial because green seeds indicate high chlorophyll content, which is undesirable for oil quality and can result in significant price dockage.
The industry standard for optimal harvest timing is when approximately 60% of the seeds on the plant’s main stem have begun this color change. Since canola is an indeterminate crop, the seeds at the base of the plant mature first. Farmers must carefully scout multiple areas of the field, opening pods on the main stem to assess the color change accurately.
The seed’s moisture content must also be within a specific range for harvest and storage. Combining should not begin until the moisture level is at or below 10%, with 8% to 10% being the target range for safe storage. Harvesting too early increases the risk of spoilage. Waiting too long increases the risk of yield loss due to shattering, where the brittle pods burst open and drop the seed.
Essential Pre-Harvest Steps: Swathing and Desiccation
To manage the risk of shattering and to promote uniform drying, farmers often employ preparatory steps in the days or weeks immediately preceding the final combine harvest. Swathing, or windrowing, is a common practice, particularly in northern regions and Canada. It involves cutting the crop and laying it in rows on the stubble to cure.
Swathing is typically implemented when the seed moisture content is higher, around 30% to 40%, and the seed color change is between 40% and 60% on the main stem. Swathing allows the plant to dry down more quickly and evenly while protecting the pods from wind and hail damage, which are major causes of shattering loss.
Once swathed, the crop generally requires 5 to 14 days in the windrow to complete curing and dry down to the final target moisture content of 8% to 10% before a combine can harvest it. Swathing during the cooler morning or evening hours is recommended to allow for a slower, more complete drying process, which aids in clearing the undesirable green color from the seed.
An alternative method is chemical desiccation, particularly for modern varieties with improved shatter resistance. This involves applying a herbicide to the standing crop to stop growth and promote rapid drying. This option is often chosen to even out maturity differences across the field and to control green weeds.
Desiccation is applied when approximately 85% of the seeds on the main stem have changed color, which is later than the timing for swathing. The desiccant typically requires 4 to 7 days to fully dry the crop before the combine can move in for a direct harvest.