Moss in Lawns

A frequent complaint in the management of lawns and grounds, especially residential lawns, is moss. Moss can be particularly noticeable in turf areas in spring, when green-up is still in process and growth has not begun in earnest. While the level of tolerance to moss varies – a few even enjoy the character that it brings to certain sites – the presence of moss is more often considered a nuisance due to physical and visual disruption of the turf.  In some cases, moss growth creates a slippery surface that can present safety concerns.

Moss most readily appears when there is a problem with the growing environment and/or maintenance practices on a property. Quite simply, any conditions that result in compromised turfgrass vigor will allow the moss to compete more successfully with desirable grasses. Reasonably effective moss control products are available that may provide temporary control, but the moss will almost certainly re-appear unless the underlying cause(s) of the problem are corrected.

When attempting to deal with a moss problem, the following may be productive options.  Implementing as many of these as possible, to the greatest extent possible, will increase the capability of turfgrasses to successfully compete with moss:
 

• Reduce irrigation frequency:  Moss growth is promoted by moist conditions. Schedule irrigation by withholding until the earliest signs of turf moisture stress, and at that point water deeply (this practice is known as wilt-based irrigation).  Deep, infrequent irrigation will keep the soil surface drier compared to shallow, frequent events which result in the surface being wet for longer periods of time.
   
• Increase water infiltration into the soil: Aim to move water quickly from the surface (where it benefits the moss) to the root zone (where it benefits the turf). This could involve practices such as dethatching (to remove excess thatch), aeration (which disrupts the thatch, the soil surface, and the root zone below to help enhance infiltration), or multiple cycling of irrigation events (providing the necessary amount of irrigation in shorter episodes rather than in one long burst to reduce puddling).
   
• Correct pH: Acidic soil conditions (relatively common in the Northeast) will enable mosses to compete more readily with desirable turfgrass species.  Test soil pH regularly and use appropriate liming practices if necessary to achieve a pH closer to the neutral range (6.5 is a good target for most lawns).
   
• Optimize nitrogen (N): Among all plant nutrients, turfgrass growth is most responsive to N, and a lack of turfgrass vigor could be due to insufficient N.  Be aware, however, that proper N rates are a careful balancing act between an amount required to sustain a desirable pace of growth, and excess that can lead to waste and loss and comprimised plant and environmental health.  Maximum N availability is best timed to coincide with peak plant activity, to maximize uptake and utilization.  For more guidance, see the Soil and Nutrient Management chapter of our Lawn and Landscape BMP document (Chapter 7), especially Table 12 on Page 68.
   
• Reduce phosphorus (P):  Moss species generally thrive on available P.  On many New England soils, P input can often be reduced or eliminated with established turf unless deficiency is indicated by a soil test.  Additionally, minimizing P inputs reduces potential for water pollution.  Remember to account for all sources of P in the management program (which can be sources like compost, soil amendments, or retained clippings, in addition to fertilizer), and if a soil test indicates a need for P, follow recommendations carefully.
   
• Incorporate iron into the fertility program: Commercial moss control materials very often contain iron (most often in the form of ferrous sulfate) as an active ingredient, which works by desiccating moss.  Iron can also be supplemented regularly along with fertilizer applications to help keep moss at bay.  This can be done conveniently because many readily-available, complete fertilizer materials these days are formulated with iron... check labels for details.  As a bonus, iron supplementation also promotes chlorophyll production, which can enhance green color.
   
• Maintain turf density: A dense turf stand is the first line of defense against invaders, as it enables fewer openings for moss and other weeds to establish and persist.  Achieve good density with appropriate cultural practices, and maintain it with overseeding and repairs as-needed.
   
• Reduce shade and increase air circulation: Possible steps might involve pruning of trees and shrubs, or even tree removal. These decisions come down to a matter of priority between the turf and other desirable plants in the landscape. In many cases there is little that can be done about shade or microclimate effects caused by structures. 
   
• Plant better adapted grasses: Based on the previous, selecting more shade tolerant grasses, for example, can be one component in an integrated strategy for managing problems from shade. Generally, if the growing environment suffers from stress factors that are not easily remedied, consider planting better adapted grasses that will compete more effectively given the conditions.  Additional examples... fine leaf fescues often perform better relative to other cool-season grasses under shaded or low pH conditions, while perennial ryegrass has superior resistance to higher traffic levels.