Clover is a common plant found in various landscapes, from manicured lawns and garden beds to agricultural fields. While often considered a simple ground cover or even a weed, its underlying root system is quite distinctive. This unique root structure plays a significant role in how clover grows, spreads, and interacts with its surrounding environment. Understanding these subterranean networks provides insight into the plant’s resilience and its ecological impact.
Understanding Clover Root Systems
Structure and Depth
Clover plants primarily develop two main types of root systems. White clover (Trifolium repens), a widespread variety, typically forms a shallow taproot system, with most roots in the top 8 inches of soil. This central root can extend downwards, sometimes reaching depths of 6 to 10 inches, providing some degree of drought tolerance and anchorage for the plant. Its primary function is to anchor the plant and access deeper moisture.
Many annual clover varieties, such as crimson clover (Trifolium incarnatum), tend to develop more fibrous root systems. These consist of a dense, shallow network of fine roots that spread out horizontally in the upper few inches of the soil. Both taproots and fibrous roots in clover are characterized by the presence of small, rounded growths called root nodules. These nodules are specialized structures that house beneficial bacteria. Within these root nodules, a symbiotic relationship occurs with Rhizobium bacteria, which are crucial for the plant’s ability to fix atmospheric nitrogen. These nodules are typically pinkish or reddish inside when active, indicating the presence of leghemoglobin, an oxygen-binding protein. The presence and health of these nodules are directly tied to clover’s unique soil-enriching properties.
Spreading Mechanisms
The root systems of clover also contribute significantly to its propagation and ability to form dense patches. White clover, in particular, is well-known for its stoloniferous growth habit. Stolons are above-ground horizontal stems that creep along the soil surface. At regular intervals along these stolons, nodes develop, from which new roots emerge and establish new plantlets. Each rooted node can live as an independent unit if it becomes isolated from the rest of the plant.
As these new plantlets root into the soil, they create a vegetative connection to the parent plant, allowing clover to spread rapidly and colonize open areas. While less common, some clover varieties, particularly certain perennial types, may also exhibit rhizomatous growth. Rhizomes are underground stems that similarly produce roots and shoots from their nodes, contributing to horizontal expansion beneath the soil surface. This combination of rooting mechanisms allows clover to form a persistent and extensive ground cover, effectively outcompeting other plants in certain conditions.
The Benefits of Clover Roots
Nitrogen Fixation
One of the most significant benefits derived from clover’s root system is its capacity for nitrogen fixation. This process is facilitated by the symbiotic relationship between clover roots and specific strains of Rhizobium bacteria residing in the root nodules. Atmospheric nitrogen, which is abundant but unusable by most plants, is converted into ammonium, a form that plants can readily absorb and utilize for growth. This natural process effectively enriches the surrounding soil with a vital nutrient.
As clover plants grow, mature, and eventually decompose, the fixed nitrogen within their tissues is released back into the soil, becoming available to neighboring plants. This reduces the need for synthetic nitrogen fertilizers, promoting more sustainable gardening and agricultural practices. The continuous cycling of nitrogen through clover roots contributes to overall soil fertility and supports the health of the entire plant community.
Soil Health and Structure
Clover roots also play a substantial role in improving overall soil health and structure. Their extensive network, whether taproots or fibrous systems, helps to break up compacted soil, creating channels that enhance aeration and water infiltration. This improved soil structure allows for better gas exchange, benefiting other plant roots and soil microorganisms. The increased porosity also ensures that water can penetrate deeper into the soil profile rather than running off the surface.
The dense mat formed by clover’s spreading roots provides excellent erosion control, particularly on slopes or in areas prone to wind and water erosion. The roots bind soil particles together, preventing their displacement and maintaining soil integrity. Furthermore, as clover plants naturally die back, their root systems decompose, contributing organic matter to the soil. This organic matter improves soil fertility, water retention, and microbial activity, fostering a healthier growing environment.
Managing Clover in Your Landscape
Encouraging Clover Growth
For those seeking to leverage clover’s benefits, encouraging its growth involves understanding its root system preferences. Clover thrives in moderately fertile soil with a pH between 6.0 and 7.0. Ensuring adequate moisture, especially during establishment, supports the development of a robust root system and active nitrogen-fixing nodules. Avoid excessive applications of nitrogen fertilizer, as clover can produce its own, and high external nitrogen levels can suppress the activity of the Rhizobium bacteria in the root nodules.
When considering clover as a lawn alternative or cover crop, proper seeding techniques ensure good root establishment. Overseeding existing lawns with microclover, for example, allows its shallow roots and stolons to integrate without overwhelming the grass. Regular mowing at a higher setting can also encourage horizontal spread and denser root development, creating a resilient and low-maintenance ground cover.
Discouraging and Removing Clover
When clover is considered undesirable, its persistent root system and spreading habits can make removal challenging. Manual weeding is effective for small patches, but it is important to remove as much of the taproot as possible and all stolons to prevent regrowth from rooted nodes. Leaving behind even small segments of stolons or taproot can lead to the plant re-establishing itself.
Cultural practices can also help discourage clover. Maintaining a dense, healthy lawn through proper fertilization, mowing, and watering can outcompete clover for light and nutrients. Since clover tends to flourish in soils that lack nitrogen, applying a high-nitrogen fertilizer that favors grass growth can shift the competitive advantage. Increasing shade by allowing grass to grow taller can also suppress clover, as its roots and stolons prefer full sun.
For larger infestations, targeted herbicides designed for broadleaf weeds can be effective, but careful application is necessary to avoid harming grass. Smothering large patches with opaque material to deprive them of light and air can also be an effective method.