Alfalfa (also known as lucerne) is a high-value forage crop cultivated worldwide, prized for its high protein content and deep root system. Alfalfa is a perennial plant, meaning its root system and crown survive the winter and regenerate new stems and leaves each spring. While biologically perennial, a stand’s practical life is ultimately determined by its anatomy and careful management.
The Structure That Allows Regrowth
The perennial nature of alfalfa relies on two specialized underground structures: the crown and the deep taproot. The crown is the compressed, fleshy base of the plant, located at or just below the soil surface, from which new stems emerge each growing season. This crown functions as a storage and regeneration center, continuously developing new buds that sprout after each harvest or during the spring green-up.
The second structure is the robust, deep taproot, which can penetrate the soil to depths of 15 to 20 feet or more. This taproot accesses deep soil moisture, making alfalfa highly drought-tolerant compared to many annual crops. For perennial survival, the taproot stores large reserves of carbohydrates, which act as the plant’s energy source.
Stored carbohydrates are consumed for energy when the plant breaks winter dormancy or regrows after cutting, before enough leaf area exists for photosynthesis. During cold periods, the plant enters a state of dormancy, relying entirely on these root reserves to survive freezing temperatures and low light conditions. The health and robustness of the crown and taproot directly determine the plant’s ability to regenerate year after year.
Typical Productive Lifespan
While alfalfa is biologically capable of living for many years, the typical productive lifespan of a commercial stand is limited to between three and eight years. This range is influenced by the specific variety’s genetics, local climate, and the presence of pests and diseases. Yields usually peak in the second year of production before beginning a gradual decline.
The eventual thinning of the stand is caused by natural plant aging, cumulative physical damage, and disease accumulation. Physical damage to the crown from repeated harvesting or wheel traffic creates entry points for crown and root rot pathogens, major contributors to stand decline. Once the plant density drops below an economic threshold—often cited as six plants per square foot—the stand becomes less profitable due to lower yields and increased weed competition.
The rate of this decline varies greatly; some stands may only last two to three years under intense management or poor conditions, while others can remain viable for eight years or longer. Selecting a variety with high genetic resistance to common local diseases and a high level of winter hardiness is important for extending the productive life of an alfalfa field.
Management Practices and Longevity
Maximizing the perennial nature of alfalfa requires careful management focused on protecting the crown and maintaining root health. The timing and height of harvest are important, as cutting too frequently or too low depletes the carbohydrate reserves needed for regrowth. Allowing the plant adequate time to replenish root carbohydrates between cuttings ensures a vigorous recovery and maintains stand longevity.
Proper fall management is essential for winter survival, as the plant must store enough energy before the onset of dormancy. The last cutting in the fall should be timed to either allow four to six weeks of regrowth before a killing frost, or to be cut late enough that no significant regrowth occurs. Leaving a slightly taller stubble height, four inches or more, helps capture snow, providing insulation that protects the crowns from extreme cold.
Maintaining optimal soil conditions is another management factor that directly impacts the plant’s ability to persist. Alfalfa thrives in deep, well-drained soils with a near-neutral pH, ideally between 6.5 and 7.0. Regular soil testing and the application of nutrients, particularly phosphorus and potassium, are necessary to support the high nutrient demands of a perennial crop and enhance winter survival. Poor drainage, however, can quickly lead to root disease and stand failure.