Alfalfa is a cornerstone forage crop globally, valued for its high protein content and digestible fiber. Cultivating high-quality alfalfa requires a careful management decision centered on harvest timing. The fundamental challenge for producers is balancing the trade-off between maximizing the total forage yield, which increases as the plant matures, and preserving the nutritional quality, which declines rapidly after a certain point. Determining the precise moment to cut the crop is the primary factor that dictates the feed value. This timing decision is complex, relying on a blend of visual observation, environmental tracking, and scientific measurement.
Primary Visual Indicators for Harvest Timing
The most traditional method for deciding when to harvest alfalfa relies on observing the physical development of the plant. As the alfalfa plant matures, its stem structure becomes more fibrous, which directly lowers the overall digestibility of the forage. Producers often aim for the bud stage to the early flower stage, as this window represents the best compromise between quantity and feed value.
Harvesting during the late bud stage, before any flowers are visible, typically yields the highest nutritional quality. At this point, the plant has high concentrations of Crude Protein and its fiber is most digestible. Delaying the cut into the early flower stage, defined as when approximately one-tenth of the stems show open flowers, significantly increases the dry matter yield. However, this delay also causes a rapid decline in the plant’s nutritional value.
Once the plant progresses beyond the 1/10th bloom stage, the quality decreases sharply because the plant is diverting energy into reproduction rather than leaf and protein production. While a later cut provides a higher tonnage per acre, the resulting forage is better suited for livestock with lower nutritional demands, such as beef cows, rather than high-producing dairy animals.
Influence of Environmental Conditions on Cutting
The plant’s maturity is not governed by the calendar alone, but also by the environmental conditions it experiences, particularly temperature. Accumulated heat units, known as Growing Degree Days (GDD), are a more accurate measure of the plant’s physiological progress than simply counting calendar days. The GDD calculation for alfalfa uses a base temperature of 41 degrees Fahrenheit, reflecting the temperature required for growth to occur.
Tracking GDD is particularly useful for predicting the timing of the First Cut of the season, which often has the highest yield but is subject to unpredictable spring weather. For instance, a period of cool, wet weather slows the accumulation of GDD, allowing the plant to add more biomass without a corresponding rapid decline in quality. Conversely, a sudden heat wave can accelerate maturity, causing the feed quality to plummet quickly.
For example, a target of 680 GDD, typically starting accumulation on March 1st, is often correlated with a Neutral Detergent Fiber (NDF) level of about 38% in the standing crop. The GDD method is generally less reliable for later cuttings because soil moisture becomes a limiting factor in summer, overriding the sole influence of temperature on growth.
Using Quality Metrics and Predictive Tools
Modern harvest decisions rely heavily on objective metrics to achieve specific nutritional targets for different classes of livestock. Neutral Detergent Fiber (NDF) is the primary scientific indicator used to predict the amount of forage an animal can consume. A lower NDF percentage signifies higher quality, as it correlates with greater digestibility and intake potential.
High-producing dairy cows require forage with a final NDF concentration of approximately 40%, which is a benchmark for maximizing milk production. To achieve this 40% NDF in the final product, the standing crop must be cut earlier, since the NDF level will increase by two to six percentage units during the harvesting, drying, and storage process. The NDF percentage of standing alfalfa can increase by 0.5 to 0.7 units each day in warm weather, creating a narrow harvest window.
To manage this narrow window, producers use tools like the Predictive Equation for Alfalfa Quality (PEAQ) stick. This simple, on-farm tool provides a rapid estimate of the standing crop’s NDF content before the time required for laboratory analysis. The PEAQ method works by correlating the height of the tallest stem and the maturity stage of the most developed stem within a two-square-foot area to an estimated NDF value. While PEAQ does not replace a final laboratory analysis, it is a valuable guide for growers to begin their harvest operations precisely when the standing crop is predicted to be at the desired quality level.