How to plant a tree
Wonderful posters from Bonnie Appleton

The following links provide descriptions, cultural requirements, and more information about each plants role in CPTED.

Access Control
Trees:
Devil's Walkingstick,
Hawthorn,
Honeylocust,
 Osage Orange,
Toothache Tree,
Trifoliate Orange,
Shrubs:
Adam's-needle Yucca,
Spanish Bayonet Yucca,
Barberry,
Cotoneaster,
Firethorn,
Hollies: Mahonia,
Flowering Quince,
Junipers,
roses
Perennials:
Pampas Grass

Territoriality
Evergreen: Atlantic White Cedar,
Columnar Junipers,
American Arborvitae
Deciduous:
English Oaks
 

Natural Surveillance

So much to add.... so little time.

The ultimate goal for matching the best tree for a particular site is to allow the tree to grow to maturity so it can provide maximum benefits to the owner and community. Don't purchase a tree and then make it "fit" into the landscape. There are at least three characteristics that should be considered when playing matchmaker. First, a thorough inventory should be performed on the cultural conditions of the site so that the tree has the potential for growth. Second, the purpose of the space should be identified and kept in mind during the tree selection and installation. And finally, it should be determined what role an individual plant, or group of plants, will play in supporting the basic components of CPTED.

Cultural Conditions of the Site 
In order for any plant to reach its ultimate height, shape, and health, the soil must be capable of supporting root growth by providing air, water, and nutrients. Selected plants should belong in a particular climate as recommended by the USDA Plant Hardiness Zone. Furthermore, one must consider the urban toughness of the plant since it will be exposed to compacted soil, heat, drought, and pedestrian traffic. Making an attempt to plant native species is a noble gesture and may be a welcomed source of food and shelter for area wildlife, but more urban-tough species may be necessary if the soil and surrounding environment is extreme.

Purpose of the Space  
Trees can provide many ecological, economical and societal benefits. For example, large deciduous shade trees strategically planted in the south and west of a building can provide significant savings on air conditioning costs. For additional information on the benefits provided by trees in urban areas, explore my urban forestry module. Identifying the purpose of a space and then making appropriate physical and behavioral adjustments to support the intended purpose is a key component to CPTED.

Are the plants still appropriate for the space? Don't be shy about recommending replacements. The purpose of different areas in a residential landscape are bound to change over time (i.e. kids grow up, homes change ownership, plants outgrow their original space). Not to mention, the homeowner may be getting on in years and not able to maintain the landscape as he did in the past. The same is true for many commercial properties following property transfers. [maintenance concerns with certain tree species have been listed on the maintenance page] 

Here are just a few plant selection criteria to consider: (as time permits I'll be adding more)

• avoid fast growing trees and other trees that are susceptible to storm damage. For example, ornamental pear trees have poor branch structure and loose large limbs during moderate snow and ice storms resulting in lopsided crowns and large permanent wounds along the trunk.
• avoid trees that are susceptible to insect and disease pests.
• avoid installing large growing trees in places where they may grow into a conflict with overhead or underground utilities.

Components of CPTED
Access Control
Trees and shrubs selected for access control should provide two things: a compact form and a painful anatomical feature to reinforce pedestrian compliance with staying on the intended path. One drawback to working with plants that fit the above description is the challenges associated with pruning and maintaining these plants. Without proper maintenance, trees and shrubs installed to encourage access control may actually end up blocking natural surveillance and working against territoriality. 

Territoriality
It’s important to not confuse the selection and training of trees and shrubs for territoriality with the creation of a “green wall” which will provide screening and privacy (and decrease natural surveillance). The goal of landscaping to support territoriality is to communicate to the public ownership of property. For example, evergreen trees can mark property lines year round. Slow growing, columnar shape trees and shrubs will remain compact and not spread over property lines or block natural surveillance. Make sure tree selection matches the property owner's desire to keep up with mainteneance. For example, fruit trees require a significant more amount of time and energy to maintain (pest problems, pruning needs, dropping fruit, etc) than a small ornamental flowering tree. Usually, pest problems and poor vigor occur for three reasons: first, the individual failed to properly select an appropriate tree for a particular site (see cultural site conditions above); second, the individual failed to research the plant material and selected plants lacking insect and disease resistance; and finally, because the individual failed to take maintenance into account when purchasing plants.

Natural Surveillance
Large shade trees can help create areas in the landscape where intended users will congregate and provide natural surveillance (porch, gazebo, water garden, etc). Trees come in a variety of shapes and sizes. At one end of the spectrum are excurrent trees, like pine and spruce trees, which consist of one central leader and limbs of decreasing length proceeding up the trunk. At the other end of the spectrum are decurrent trees, like elms, which consist of a number of codominant leaders. Large decurrent trees provide excellent shade and are able to avoid conflicts with the ability of pedestrians to provide natural surveillance since the canopy is elevated. Excurrent trees, on the other hand, work against natural surveillance since the majority of the tree’s canopy is close to the ground blocking the ability of individual’s to perform natural surveillance. Inspect large decurrent trees growing near homes and buildings and have limbs pruned that may provide climbing access to upper story windows/rooftops.

Flowering trees can serve as focal points at different times of the growing season. Usually only one or two different species are needed per residential property. As a focal point it should promote natural surveillance by giving the neighbors and pedestrians something to view.

In order for street and parking lot lamps to help conditions for natural surveillance, it's important that the light reaching the ground provides uniform illumination. Trees located along streets and in parking lots shade areas resulting in dark areas and hinder natural surveillance. Avoid installing trees that provide dense shade (Norway maple) and consider trees that provide light partial shade (honey locust).