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Remedial

When plant withers or becomes non-productive or diseased, it should be removed by pruning. Plants if pruned badly may grow undesirably or even become diseased¹.

Pruning Guidelines

Trees

Rooftop trees are pruned to remove the diseased and unwanted twigs and branches and control the height and shape of the rooftop tree. A thinner crown also enhances airflow and reduces wind load on the tree crown. Over-pruning should be avoided as pruning cuts are susceptible to disease infection. The tree crown should not be pruned more than 25%.

Tools

For saplings, tools such as curved pruning saw, loppers and secateurs should be used to make formative pruning.
Branches with less than 80mm in girth should not be pruned with chainsaws.

Pruning Standards

Use “3-point cut” method (target pruning) –  cut from below (1), top cut (2) and final cut (3) to avoid bark tearing.
Prune according to the branch collar or  branch bark ridge
Avoid leaving a stub unless the branch collar is not identifiable, leave a stub to prevent damaging the tree.
Prune closely to the branch collar without cutting into it.

Procedure

Study the tree form and select the best spaced and positioned permanent branches.
Clean the crown by removing the diseased, dead, broken and parasitic plants.
Thin the crown by removing branches to enhance light penetration and airflow and to minimize wind load on the branches.
Reduce the crown (overall height and spread of tree) by cutting the terminals and scaffold branches back to laterals that are large enough (minimum of 1/3 the diameter of the main supporting branch) to support the growth of the limb. Prune accordingly to the “Pruning Standards”.
Spacing of branches on the trunk should be around 0.15 to 0.5m apart for permanent branches depending on the maturity of the trees. 0.3m to 0.6m spacing is ideal for matured trees, otherwise 0.15m spacing is adequate.
Remove fast growing tree suckers at the base of and along the trunks. Leave water sprouts along branches unless it becomes overcrowded. Pruned away weaker sprouts and prune back long and sizable ones to reduce growth of sprouts and ensure adequate attachment for the size of the sprouts.

 Safety

Cordon off the area under which tree pruning operations are being carried out  including the ground floor area where the tree situated near the roof edge is being pruned.
Ensure that no pedestrians and vehicles enter the drop zone at the ground level.
Appropriate equipments and adequate skilled personnel must be employed to ensure site safety and adhere closely to the procedure.
Special care must be taken when pruning trees near rooftop edge to prevent falling debris. Pruning works shall conform to the standards specified in ANSI A300 Part 1.

Palms

Rooftop palms are pruned to remove withering or damaged fronds, fruit stalks and to prevent overgrown clustered palms. Over-pruning should be avoided as the removal of excessive fronds weakens the palm as photosynthesis is reduced. Mature fronds provide protection to the growing fronds. Pruning cuts are also susceptible to disease infection.

Procedure

Remove only withering, browning or damaged fronds. Do not remove more fronds than the palm can be produced in a year.
Fronds should not be pruned too close to the trunk of the palm to prevent damaging the palm trunk. Care must be taken not to damage the terminal bud/spear to prevent the palm from dying.
Large and heavy falling fronds of palms such as royal palm (Roystonea regia) may damage property and cause injury, thus measures must be taken to prevent these hazard.
Large fruits of coconut palms (Cocos nucifera) may pose hazard to pedestrians and vehicles passing under the palms. Safety precautions such as planting the palms away from human and vehicular traffic.
Employ skilled personnel to prune rooftop palms by using cutting tools and equipment such as aerial platform for taller palms.

Shrubs

Remove all dead, diseased, damaged and unwanted branches to prevent shrub from becoming too large or dense.
Prune back long branches to a bud or lateral branch to 0.15 to 0.3m below the desirable shrub height.
Prune each branch separately to different lengths with secateurs if the shrub is 0.15 to 1.0m too tall.
Special care must be taken when pruning shrubs along roof edges to prevent falling plant debris.
Considerations should be taken during design phase for effective maintenance of shrubs along roof edge and for safety of workers.

Hedges

Clip hedges while the new growth is succulent and green.
Trim hedges such that the base is wider than the top.
Plant taller hedges along the roof edge to provide shelter from strong winds or from view. Special care must be taken when pruning hedges along roof edges to prevent falling plant debris.
Considerations should be taken during design phase for effective maintenance of hedges along roof edge and for safety of workers – such as setting back tall hedges to allow outermost surface of the hedge foliage can be inspected and pruned when needed.

Mulching Guidelines

Mulching is only carried out when necessary with no schedule to follow. After planting, mulch the trees and shrubs immediately and replenish when the thickness has reduced.

Useful reference website: http://mygreenspace.nparks.gov.sg/how-to-mulch-your-trees-shrubs/

Trees

Before application of mulch, remove any vegetation around the base of the tree trunk.
Create a 0.3 to 0.5m wide (depending on size of tree) circular vegetation-free border around collar of the tree.
Spread the mulch to the desired thickness not exceeding more than 100mm thick.
Fork the mulch materials slightly into the soil.
Water the mulch to settle it.
Maintain a zone of 50mm to 80mm around the collar tree trunks or palm without mulch materials.

Shrubs

Clear away any weeds or leaves around the base of the stems.
From a border of about 100mm around but a minimum of 20mm away from the base of the stem.
Manually spread a 20-30mm thick layer of mulch.