Trifolium species, commonly known as clover, is a genus of legumes. The plant is frequently utilized as a forage crop for livestock due to its high protein content, a low-maintenance lawn alternative, and an effective cover crop for soil health. Clover’s ability to fix atmospheric nitrogen into the soil through a symbiotic relationship with rhizobia bacteria is a defining characteristic, reducing the need for synthetic nitrogen fertilizers. The question of when clover produces viable seeds is central to both harvesting the plant and managing its spread in a mixed landscape.
The Seasonal Timing of Clover Seeding
Clover begins the process of seed production after receiving specific environmental signals. The primary triggers for flowering and subsequent seeding are increasing photoperiod, which is the duration of daylight, and sustained warm temperatures. This generally places the onset of flowering in late spring, with the true seeding process beginning shortly thereafter.
In temperate climates, the window for viable seed development typically spans from late spring through mid-summer. While flowers may appear in May, the seeds inside the florets require several weeks of warm conditions to become fully ripe and capable of germination. The flower heads must remain on the plant long enough for the reproductive cycle to complete.
The precise timing varies geographically, but as temperatures consistently exceed 59 degrees Fahrenheit, the plant’s growth accelerates, moving it toward the reproductive stage. This predictable response to light and heat ensures that the seeds mature during the most favorable part of the growing season.
The Biological Process of Seed Formation
The journey from a flower head to a viable seed head involves a defined sequence of biological steps that starts with the inflorescence. Each clover flower head, or capitulum, is actually a dense cluster of many small individual flowers called florets, which can number from 50 to 150. These florets must be pollinated, typically by insects such as honeybees or bumblebees, which transfer pollen from one flower to another.
Once a floret is successfully pollinated and fertilized, the ovules inside the ovary begin to develop into seeds. Each floret contains tiny seed pods that hold between four and seven ovules, though only an average of about three seeds per floret typically reach maturity. The entire development process, from fertilization to full seed ripening, takes an average of approximately 26 days.
For the seeds to be considered mature and viable, the entire flower head must dry out and turn a brown or black color. The tiny seeds are contained within a thin, dry pod that remains hidden inside the remnants of the old flower structure. This maturation is characterized by the seeds hardening, which is a necessary step for successful dispersal.
Seeding Differences Among Common Clover Species
Seeding habits differ significantly among the most widely cultivated clover types, influencing management strategies.
White Clover (Trifolium repens), a perennial, is a continuous seeder throughout the summer months. It produces flowers on low-growing stolons, allowing it to flower, set seed, and spread laterally simultaneously, resulting in a prolonged seed production season.
Red Clover (Trifolium pratense), a biennial or short-lived perennial, has a more distinct and vertical growth habit. Seed production in red clover typically occurs in cycles, often after a first cutting is taken for hay or forage. Farmers often harvest seed from the second or third growth cycle later in the summer, as these periods are more conducive to high-quality seed set.
Crimson Clover (Trifolium incarnatum) is primarily grown as a winter annual, with a quick and aggressive growth cycle. It flowers early in the season and produces its seed rapidly before the plant dies back, usually by early summer. This species is favored when a quick burst of nitrogen fixation and a single, predictable seed crop are desired.
Managing Clover Once Seed Heads Appear
Management actions taken after clover begins to flower depend entirely on the desired outcome—either encouraging seed production or preventing it. If the goal is to harvest seed or promote natural reseeding, the flower heads must be allowed to fully mature on the plant. Seed harvest is ideally timed when the majority of the flower heads are completely dry and have turned a distinct brown or black color.
For those aiming to prevent clover from seeding, such as in a lawn or pasture where vegetative growth is preferred, timely mowing is the most effective control method. Mowing should be done frequently enough to remove the flower heads before the seeds inside have a chance to ripen and become viable. The mowing height is important; cutting the clover at a high setting, often four to five inches, helps stimulate new vegetative growth while still clipping the flower heads.
Mowing interrupts the plant’s reproductive cycle, preventing the spread of new seeds into the surrounding area. Conversely, if the clover is being grown for forage, a strategic cutting can be timed to encourage new leaf growth and stimulate a second, more robust flowering cycle for later seed harvest.