Since I have replaced my 1919 Underwood typewriter with a more contemporary computer for ‘word processing’, I have found the ‘copy’ and ‘paste’ functions to be very useful during the composition of most of my arborist reports. With very few exceptions, the inspections of commercial sites that I’ve conducted with a local tree care company invariably include the equivalent of “Irrigation is too frequent to adequately drain from the endemic dense soil. Consistent saturation of soil has inhibited development of a healthy root system. . . “

Unfortunately, the various species within most landscapes require specific but different duration and frequency of either drip or sprinkler irrigation. Lawns and most annuals only extend roots into the upper few inches of soil. Consequently, frequent, but not necessarily generous irrigation is necessary to prevent desiccation of the surface soil and the roots contained within it. However, most trees and other more substantial species prefer less frequent, but generous irrigation that will penetrate to lower soil without maintaining saturation.

If irrigation is both frequent and generous, surface soil may sustain lawns and annual species, but lower soil is more likely to be too saturated for roots of larger species. I occasionally inspect areas that are so saturated that even annuals or lawn grass can not survive! The most effective solution to the problem is obviously adjustment of irrigation.

Trees and shrubs require frequent irrigation when initially installed because roots are confined to such a small volume of soil. Some garden enthusiasts prefer to install ‘watering tubes’, which are merely empty vertical pipes that extend approximately eighteen inches below the surface of the soil. Infrequent but generous irrigation applied directly into these pipes may promote development of deeper root systems, but only if surface irrigation is minimal and soil is not consistently saturated.

Organic soil amendments temporarily improve drainage during the time that new specimens are becoming established. By the time the amendments decompose, the new specimens should have become established and no longer require enhanced drainage. Although gravel at the bottom of containers may improve drainage (until clay settles into it), it does little, if anything to improve drainage in soil because clay immediately adheres to it when moist. Gypsum or gypsum substitutes improve drainage by leaching out soluble salts that cause clay particles to coagulate.