March 30, 2009

Mulching vs. Lawns at the Arboretum

written by Francis ChingLasca Leaves 20:37, 1970For many years mulching practices at the Arboretum were carried on only to a limited extent. One reason was that since the Arboretum is adjacent to the Santa Anita Race Track, a great number of residents in the immediate area have always been conscious of flies and have related any kind of mulching and composting with fly infestation. Many times in the past, the Arboretum has been able to obtain manure as well as bedding material from race tracks, yet, despite thorough inspections by the County Health Department, the fly problem has been erroneously blamed on the Arboretum.Another reason why mulching practices have been resisted is that it was thought the general public would not appreciate large mulched areas as compared to a well-manicured lawn.Further, there was the question of salts and possible damage to plants from an accumulation of salts from manures. In the final analysis, it was determined that if manure were properly used as a mulch, salts, if present in even damaging proportions, would be leached away before being able to cause any damage.A fear that slopes heavily mulched would be subject to severe erosion from heavy rains or irrigation practices was thoroughly discounted by a timely demonstration. Although mulching to any extent had not been practiced since the Arboretum was started in 1949, and plants apparently grew “all right,” serious consideration was given in 1964 to a review of its advantages. lt was well known that in the early days of development, whatever topsoil there was, was scooped up, pushed around and eventually lost. Not only were there hardpans present in many areas but surface layers were also compacted due to heavy equipment causing poor aeration and an intolerable condition for adequate infiltration and percolation of moisture. It was glaringly noticeable following heavy winds in 1962, 1963, and 1964 that many trees were lost due to uprooting. All of these uprooted trees possessed a very shallow root system which made them prime candidates for “pushovers.” In addition, during digging and moving operations of large trees, many of the plants also had a very shallow root system which made moving operations quite difficult.Realizing the poor soil conditions, checks were made on actual moisture penetration. Even after a relatively heavy rainstorm of two inches in twenty-four hours, moisture penetration amounted to as little as two inches in some areas. Checks made after leaving rainbirds on for seven hours showed that moisture penetration was less than four inches.Poor Root Systems coupled with poor soil moisture penetration brought the sudden realization that irrigation practices were insufficient. This situation was worsened by the fact that it had always been more important to irrigate according to the needs of the lawn, taking it for granted that the trees and shrubs were receiving adequate amounts of moisture.Maintenance of a lawn in a heavily planted area poses many problems besides watering. Having to mow regularly between plants subjects plants to possible damage. On the other hand, if lawns are not adequately mowed, the area takes on an unkempt appearance. In order to keep all lawn areas mowed during the spring, summer, and fall months, six men were assigned to the task. This did not include the great amount of time necessary for servicing and repairing the equipment.Besides mowing, it was also necessary to spend endless hours in hand trimming grass away from the base of trees and shrubs. When this is not done regularly during the summer months, Bermuda grass has a tendency to climb up into the low branches of shrubs and up the sides of tree trunks.(This is the first part of a two-part article)