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Pruning:
This is the single most important task that contributes to the overall health and appearance of the trees. Pruning is conducted 1 (-2) times each year. The most significant pruning is done from January - early March. Specifically:
Newly Planted Trees (3-6 years after planting): The training system used is the modified leader. At the time of selection the spacing between primary scaffold limbs is approximately 6-8 (-12) inches with permanent lateral branches at least two (2) ft. out from the trunk. The size of the selected limbs at their point of attachment is approximately 1/2 (one half) or less the diameter of the trunk or parent branch.
Mature Established Trees: The objective is to maintain a sound scaffold branching system by selective thinning of branches and removal of dead, interfering, split, broken, diseased and large branches with narrow angles of attachment to ensure the development of a sound scaffold branch system, while keeping an attractive shape. No more than one-fourth (1/4) of the foliage is be removed during a single pruning operation and upon completion one-half (1/2) of the remaining foliage is on branches that originate in the lower two-thirds (2/3) of the tree. The use chain saws or circular blade power saws is limited to branches greater than 2 inches in diameter or greater. Branches less than 2 inches in diameter are removed using hand saws or scissor type pruners or loppers. The use of anvil type pruners is prohibited. When removing branches all effort is be made to cut back to a lateral one-third (1/3) the diameter of the branch being removed at its point of origin on the trunk or parent limb. The final cut is made sufficiently close to the trunk running back across the limb at a 45 degree angle, without cutting into the bark branch ridge or branch collar or leaving a protruding stub.
Watering:
Watering is performed on 1-3 year old trees as needed using water trucks. Established trees in large massings are irrigated during periods of prolonged drought with water from teh Potomac River or Tidal Basin by operating large water pumps and irrigation pipe approximately 1/4 mile in length with sprinklers every 60 feet.
Wound Treatment:
Bark tracing is performed when the bark has been damaged and there is an open wound. When repairing bark wounds only damaged or loose bark is removed to minimize the disturbance to live tissue. Wounding paints are no longer used as they have not been shown to be effective in preventing or reducing decay or preventing insect and/or disease infestations.
Insect and Disease Control:
Like all plants the cherries have their insect and disease associates but there are none that are threatening the cherries. The most common pest in is scale. The cherries are monitored for insects and diseases under an Integrated Pest Management Program and only sprayed when populations reach predetermined threshold levels.
Bacterial canker (sunken or elliptical lesions on the trunks or branches that oozes gum from the wounds) also known as bacterial gummosis, is common but is rarely a serious problem on established trees. It is controlled through pruning and/or wound treatments (bark tracing).
Fertilization:
Fertilization is only conducted to correct or prevent nutrient deficiencies. A slow release fertilizer specifically formulated for trees is used and applied by soil injection at 200 pounds per square inch (psi), 4-8 inches below the soil surface, at a rate of 2-3 lbs of actual nitrogen per 1000 square feet.
In 1998 on a very limited basis endo and ecto mycorrhizal fungi, root bio-stimulants and growth promoting bacteria was added to the fertilizer solution to help the cherries overcome stress due to low soil fertility, drought, temperature extremes and visitor use impacts.
Aeration/Vertical Mulching:
This was initiated in 1995 on a very limited scale to try to mitigate the problems of soil compaction due to recurrent visitor use. When soils become compacted, virtually all of the favorable soil physical characteristics are adversely affected. Specifically: structure, tilth, oxygen/carbon dioxide balance, soil microbiology, total and capillary spore space, and water infiltration and water holding capacity. Aeration and vertical mulching can help mitigate compaction; however; trees cannot be expected to recover and/or realize the benefits from remedial treatments, if the recurrent activities and/or visitor use patterns continue.
This procedure consists of using a highly focused supersonic air stream (app. 1,300 mph) to penetrate soil and fracture soil it away from tree roots in trenches that resemble the spokes on a bicycle wheel. The trenches are then backfilled with a mix of 1/3 sandy loam topsoil, 1/3 lightweight aggregate of expanded shale or slate and 1/3 composted leaf mold by volume.
Replacement:
All cherry trees in the Park are tagged, mapped and inventoried. Trees that die due to old age, anaerobic soil conditions (low oxygen due to flooding from the Tidal Basin and Potomac River), impacts from recurrent visitor use, or insect and disease infestations are replaced with trees purchased from commercial nurseries during the next planting season (November 1 - November 30 and March 15- April 15, weather and soil conditions permitting).
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