Why do parking lot islands of turf fail in the summertime? – Turfgrass Science at Purdue University

Why do parking lot islands of turf fail in the summertime?

Have you ever noticed that grass located in or near parking lots struggle in heat or drought conditions?  In fact, many times grassed areas in or near parking lots are great indicators of when turf is getting dry, as they are normally the first to show heat or drought stress. 

The most common reason why these grassed areas are the first to stress from heat or drought is because they are located near paved surfaces.  Parking lot islands of turf and ornamentals can be surrounded by things that have very little cooling effect, such as pavement, vehicles, or buildings. These surfaces tend to adsorb heat from sunlight and can remain significantly warmer during the day and even into the night.
Another contributing reason for turf failing in parking lots is because it is often times difficult to get irrigation needed for these areas.  Parking lot islands are normally an afterthought by developers and they are typically placed right over the same gravel layer as the rest of the parking lot.  As such, the feasibility for maintenance is normally sacrificed during construction.  Unless the developer placed irrigation lines to the grassed islands before paving, it is normally a tremendous amount of work to have irrigation installed. 

One other reason why parking lot islands fail is similar to why lawns struggle in new subdivisions: the soil is of poor quality, compacted, and shallow.  A contractor will often use soil from the sub-grade that was excavated to build the house or parking lot.  This soil commonly consists of clays that are low in organic matter and nutrients for the new lawn.  Also, parking lot islands typically have soil depths not sufficient to sustain turf through the long days of summer heat.  The deeper the soil in the parking island, the better chance the turf has of surviving and performing well. Typically, soils in these areas are heavily compacted during construction.

As a result of drought, heat, shallow soils, soil compaction, lack of nutrients, weeds will often invade parking lot islands and out-compete the weak turf. Prostrate knotweed and spurge, goosegrass, yellow nutsedge, and many more weeds will compete well in these areas.

Quite often, planting turf in a parking lot island is not always the best alternative.  The general location, shape of the island, access to irrigation, height of curb (for maintenance equipment), shade (long-term after trees grow), heat, and drought tolerance of plant species, and the suspected amount of foot traffic the area will receive should all be taken into consideration when deciding landscaping for the space. 

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