September and early October are the best times of the year to renovate or repair damaged cool-season lawns. Jason Lanier of The University of Massachusetts Extension Service recently offered in a UMass Turf enewsletter the following thoughts on the differences between a lawn renovation and a lawn reconstruction. Renovation (less disruptive) – Process of replacing the turf plants on a site without making changes to the soil or grade. Does not normally include total removal of existing turf, but usually includes eradication of the existing stand with non-selective herbicides or extended covering. May include some superficial cultivation in the interest of promoting seed-to-soil contact. Reconstruction (more disruptive) – Involves wholesale removal of existing turf on a site in conjunction with tilling or other soil cultivation, at least to the depth of the root zone or deeper. Frequently also includes addition of soil amendments, addition of topsoil, and/or changes to grade. In straightforward terms, if renovation compares to remodeling an out-of-date kitchen, reconstruction is like rebuilding the whole house (see figure below). Renovation is most appropriate when turf has deteriorated due to stress, pest damage or unadapted grasses, but the soil and overall growing environment remain generally suitable. A general guideline is to renovate when 50% or more of the turf is composed of undesirable grasses or weeds. Renovation is a great opportunity to more closely match grass species and varieties to site conditions. When there are ongoing problems that go beyond just the plants present, a full-scale reconstruction may be warranted. A decision to take on a reconstruction project should be carefully considered; as in is it necessary to start from scratch?  In modern medicine, for example, there is an effort to better tailor patient treatments to precisely fit the severity of the condition. When health problems are dire or life threatening, there is more opportunity to gain from major intervention. When issues are less severe, however, major intervention may be less appropriate because there is smaller opportunity for benefit.  In other words, the risk of net harm is increased when the degree of intervention is greater than what the problem truly requires. Decisions to ‘open’ the soil in a turf system, as is the case with reconstruction projects, should always be approached cautiously. Cultivation can damage soil structure, introduce the possibility of soil erosion, and stir the ‘seed bank’. At the same time, cultivating the soil provides opportunities not typically available in a perennial turf system including ability to incorporate fertilizer and soil amendments, improve drainage, and alter the grade. In other instances, digging may be required to remove boulders or buried debris, or to install physical infrastructure such as irrigation system components. Therefore, in the majority of circumstances complete reconstruction should be based on identifiable need or, from a strictly agronomic perspective, treated as a last resort. Compared with renovation, reconstruction is more expensive, time-consuming, labor intensive, and functionally and aesthetically disruptive. When circumstances or budget do not permit a justifiable reconstruction, a renovation approach will most often yield measurable improvement. Even in situations where the means and need for reconstruction exist, opting for renovation first may at best have satisfactory results and at least buy some time (perhaps multiple seasons) before the larger investment of funds and energy in a wholesale reconstruction project. While we’re on the subject of establishment, don’t forget the additional option of seeding into an existing, living stand. Late summer is a perfect time for overseeding, which often involves seeding into established turf in the interest of repairs or maintaining adequate density.  Other times the goal is to gradually introduce different grass species or cultivars and alter the stand composition over time; this process is sometimes referred to as interseeding. To subscribe to the free U. Mass turf enewsletter click here.