PLANT HEALTH CARE
Unfortunately , optimal levels for the various nutrients are not well documented . Dr . Carl Whitcomb and Dr . Linda Chalker-Scott have published some general guidelines , as have some local and regional soil labs . Fortunately , iron and manganese are required in relatively small quantities by most plants . The products Osmocote Plus and Micromax are good sources of micronutrients . Keep in mind that nitrogen tests are temporary in nature , as it is a mobile nutrient . As such , tests for nitrogen provide a “ snapshot ” value only , and often are unreliable from month to month .
HIGH / LOW SOIL PH Though nitrogen is hard to test for , at least it tends to be available across a wide range of soil pH , which helps with plant uptake . Most micronutrients , such as iron , magnesium and manganese on the other hand , are pH dependent , being readily available or unavailable . For example , at pH 7-9 magnesium is readily available , and much less so at more acidic pH ranges . Iron and manganese are just the opposite , being available at low pH values , in the 5-7 range , and unavailable or tied up at higher pH ranges .
Knowing this information is one thing ; being able to do something about it is quite another . The bottomline question is whether changing soil pH is a viable option for woody plants in the sports field or campus landscape . Two factors conflict with the capacity to change soil pH for trees and shrubs . First , the soil volume , especially for trees . For large woody plants , approximately 40 % of the absorptive roots are near the base of the tree , another 40 % under the canopy as it extends to the drip line , and the remaining 20 % extending outward as far as the height of the tree . It ’ s simply a large rootzone volume .
The other consideration is the difficulty in lowering and raising soil pH for the nutrients that are pH dependent for availability . For example , lowering the pH from 8 to 6.5 would require 25-50 pounds of sulfur to be broadcast and worked into the upper 6 inches of soil under the tree canopy . Some relief may be achieved by simple core aeration and topdressing with sulfur or ammonium sulfate ; however , the results from these methods are quite variable . Similar but higher amounts of lime are required to raise the soil pH from 6 to 6.5 . Both endeavors are affected by the amount of clay in the soil , requiring greater amounts in heavier clay soils .
R = RENEW Where stems with yellow leaves are localized , with symptoms being exhibited on a single or just a few branches , renewal may be in order . With trees , starting with the removal of certain branches may be successful , especially if they are infested with insects such as scale or infected with cankers . In approximately 30-40 % of the cases , this results in a complete turnaround and return to health of the tree , which amounts to a great return on investment and retention of the symptomatic specimen . Pruning in early to midspring is the best timing in most situations .
The same guideline holds true for deciduous shrubs ; removal of problematic stems at the ground level sometimes removes the symptoms and keeps the shrub in the landscape . If more than a few stems are involved , removal of all stems at the ground level is recommended , even though it may seem drastic . If the root system is otherwise healthy and the shrub has been established for three or more years , this type of renewal will eliminate the yellow leaves , increase the air circulation through the canopy and encourage new stems to replace the old ones . Total stem removal is not recommended for evergreen shrubs such as holly , arborvitae or boxwood , as it would kill the plant in most cases . Selective stem removal is encouraged instead .
R = REPLACE More or less as a last resort , if repair and renewal are not successful , it ’ s wise to cut your losses and move on to something else — either another species that is better adapted to the site or a non-plant option such as a bench , water feature or small sculpture . Consult with local horticulturists and ISA Certified Arborists regarding good options and a thorough consideration of the right plant in the right place . Proper planting procedures go a long way to preventing future issues of this type . This includes digging a hole three times wider than the root ball but no deeper ; installing the root mass such that the top lateral root is placed at or slightly above grade ; and taking time to spread out any circling roots , covering them with 2-3 inches of wood chips and keeping the roots moist , but not soggy or dry going forward . SFM
John C . Fech is a horticulturist with the University of Nebraska-Lincoln and Certified Arborist with the International Society of Arboriculture . The author of two books and more than 400 popular and trade journal articles , he focuses his time on teaching effective landscape maintenance techniques , water conservation , diagnosing turf and ornamental problems , and encouraging effective bilingual communication in the green industry . sportsfieldmanagementonline . com July 2024 | SportsField Management
23