Excessive moss or clover in a lawn are a sign that the grass isn't thriving. Consequently, controlling these weedy invaders mostly involves improving the growing conditions for turfgrass so it can defeat the competition. Mosses are threadlike, green, non-flowering plants without roots, and they love cool, moist conditions. On the other hand, clovers grow well in warm, sunny spots, but they thrive in low-nitrogen soils. Clovers that invade lawns include annual plants like California burclover (Medicago polymorpha) and black medic (Medicago lupulina), and perennials like white clover (Trifolium repens), which returns every year.
Natural Moss Control
Natural moss control in lawns involves improving drainage, lowering moisture levels and reducing shade. Chemical lawn moss killers provide a temporary solution, but as long as the conditions that encourage the growth of moss remain the same, it grows back as strong as ever. To begin your lawn improvement plan and discourage moss growth, cut back overhanging branches that shade the grass and restrict air movement. Next, water your lawn only when the soil is dry to a depth of one inch, and when mowing, only remove the top one-third of the grass blades to encourage strong, deep roots.
When the lawn isn't wet, remove the moss and the buildup of dead grass between the grass stalks with a manual or powered lawn dethatcher. Finally, improve your lawn's drainage by using a lawn corer or slicer to remove cores of soil or cut gashes, allowing air into the ground.
Natural Clover Control
Fertilizing your lawn is the key to reducing the growth of clover plants, and the grass doesn't mind if you prefer to use an organic fertilizer. A handy rule of thumb is to apply one pound of nitrogen per 1,000 square feet of lawn, but that doesn't mean you should apply one pound of fertilizer. To figure out how much fertilizer to apply, check the label for three numbers, which show the percentage of each fertilizer ingredient. The first number gives the amount of nitrogen. Now you can calculate how much fertilizer gives one pound of nitrogen. For example, if the label states 25-10-12, the product contains 25 percent nitrogen, and you need to apply four pounds of fertilizer to supply one pound of nitrogen. Apply the fertilizer at the time of year when the grass is growing strongly, wait at least a month between applications, and don't apply more than four pounds of nitrogen per year. If you already regularly apply lawn fertilizer, try switching to a product with proportionally more nitrogen and less phosphorus, which is represented in the second of the three numbers.
Hand-pulling is another natural clover control method. It works best on annual clovers, providing you remove them before they set seed. For perennial clovers, it can be difficult to pull up the whole plant including the roots. Pouring boiling water on the plants can be effective on perennial clover plants, but watch for the plants growing back and repeat the action if necessary. Remember to wear long pants and boots to protect against splashes.
Right Grass, Right Place
Problems with moss, clover and other lawn weeds are often a symptom that the turfgrass species doesn't grow well in the existing conditions. In naturally damp, shady areas, St. Augustinegrass (Stenotaphrum secundatum) and red fescue (Festuca rubra) grow better than other turfgrass species, like bermudagrass (Poa pratensis) and perennial ryegrass (Lolium perenne), which don't tolerate shade. If problems with moss and clover persist after improving the growing conditions as much as possible, it might be time to go back to the drawing board and reseed the lawn with a turfgrass mix that's ideal for the existing conditions.
- Oregon State University: Physical Moss Control for Lawns
- University of California Integrated Pest Management Program: Clovers
- University of California Cooperative Extension Ventura County: Moss
- Beyond Pesticides: Least-Toxic Control of Weeds
- University of California Integrated Pest Management Program: Turf Adaptations and Tolerances
- Penn State College of Agricultural Sciences: Calculations Used to Determine the Amount of Fertilizer Needed to Treat Turf
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