The challenge of maintaining a lawn with both grass and clover requires a highly selective weed control strategy. Standard weed killers eliminate broadleaf plants indiscriminately, destroying desirable clover along with undesirable weeds. Preserving both grass and clover while removing broadleaf weeds requires navigating the complex biology of plant families and specialized herbicide chemistry. The solution lies in finding products that exploit a narrow physiological difference between clover and other common lawn weeds.
The Science of Selective Herbicide Action
Selective herbicides target biological differences between monocots (grasses) and dicots (broadleaf weeds and clover). Grasses have parallel leaf veins and a protected, low growing point. Dicots feature net-like leaf veins and exposed growing points. This structural difference is the basis for most selective lawn weed killers.
Many selective weed control products are synthetic auxins, which mimic natural plant growth hormones. When a dicot absorbs this chemical, it triggers uncontrolled cell growth, leading to death. Monocots are generally spared because they metabolize the hormone quickly or limit chemical translocation. However, clover is often susceptible to these broad-spectrum selective herbicides.
Common Herbicides That Harm Clover
The most common lawn weed killers are cocktails of synthetic auxins, such as 2,4-D, MCPP (mecoprop), and Dicamba. These chemicals effectively control a wide range of broadleaf weeds, including dandelions, plantain, and ground ivy. They are marketed as “lawn safe” because they leave the monocot grass unharmed.
Clover is a broadleaf plant, and its physiology is vulnerable to the same synthetic auxin mode of action. Products containing 2,4-D will kill clover just as effectively as they kill dandelions. If the goal is to keep clover, products listing these common active ingredients must be avoided. Quinclorac, often used for crabgrass control, also kills clover and other broadleaf weeds.
Specialized Products That Spare Grass and Clover
Specialized chemicals and formulations exist that can remove broadleaf weeds while sparing both grass and clover. The primary chemical that avoids clover is the selective herbicide 2,4-DB, or 4-(2,4-dichlorophenoxy)butyric acid. The distinction from 2,4-D is the addition of the “B” (butyric acid) to the base structure.
This selective action occurs because 2,4-DB is inactive in its applied form. Tolerant plants, specifically legumes like clover, lack the necessary enzymes to convert the 2,4-DB molecule into the toxic 2,4-D molecule. Undesirable broadleaf weeds, however, can perform this conversion, making the herbicide active only within their tissues. This allows 2,4-DB to control susceptible weeds in clover plots, though it may cause temporary vigor reduction in the clover.
Another option is the use of iron-based herbicides, which contain the active ingredient FeHEDTA (iron chelate). This mineral-based selective herbicide works by causing excessive iron uptake in broadleaf weeds. The over-absorption of iron leads to rapid tissue damage and plant death within hours. Grasses are unharmed because they absorb the chelated iron in much lower quantities.
Non-Chemical and Cultural Weed Control Methods
Implementing cultural practices is a preventative measure that reduces the reliance on chemical applications. Maintaining a taller grass height, typically above three inches, creates shade that suppresses weed seed germination and growth. A dense, healthy turf provides competition against weeds for sunlight, water, and nutrients.
Fertilization and Spot Treatment
Proper fertilization is important, as clover often thrives in nitrogen-deficient soil where it fixes its own nitrogen. Increasing nitrogen fertilization promotes a healthier, more vigorous grass stand, which naturally outcompetes clover and other weeds. Spot-treating small weed patches is an alternative to broadcast spraying the entire lawn, preventing widespread chemical exposure.
Natural Alternatives
Natural alternatives exist for spot treatment, but they have limitations. Corn gluten meal acts as a pre-emergent herbicide, inhibiting weed seed germination, but must be applied before sprouting.
Concentrated horticultural vinegar, containing a high percentage of acetic acid, is a post-emergent option. This acid works by desiccating the parts of the plant it contacts, essentially burning the leaves and stems. However, vinegar is non-selective, damaging any plant tissue, and often does not kill the weed’s deep root system, leading to regrowth.