Arborists have a saying – “Right tree, right place.” As a corollary, there is also “wrong tree, wrong place.” Think of a monkeypod planted in a small planter – an extreme case of “wrong tree, wrong place.”

This monkeypod was planted between a curb, a sidewalk, and a driveway. Note the large root pruning wounds near the root flare. The tree was removed shortly after this photo was taken.

            So how do we, as landscape professionals, stay toward the “right tree, right place” end of the spectrum? What do we need to consider when we’re thinking about planting a tree? Here’s a list of basic items that should be taken into account before we plant trees:

  • Mature size of the tree – height, spread, root flare, overall shape
  • Rate of growth
  • Native/non-native – is it invasive?
  • Planter size – sufficient space, volume of soil, distance to structures
  • Sun/shade exposure and tolerance
  • Irrigation availability
  • Soil – pH, salt content, texture
  • Utilities – overhead and underground
  • Resistance to pests and diseases
  • Drought or wet tolerance
  • Drainage – good, fair, or poor
  • Maintenance issues – messy fruits/flowers/leaves, tendency for surface roots, poor structure/weak wood

    This young kou tree growing into the side of the adjacent building is approximately 5’ away. At its mature size, the spread of a kou’s crown is up to 25’ wide. It will take frequent, costly maintenance to reduce the crown by the building to protect the siding. Roots are also a concern. A tree’s roots extend 2-3 times the crown of the tree. As this tree matures, its roots are likely to damage the building foundation.

        Many of us can look at an existing landscape, run through most of these items automatically in our heads based on past experience with trees in similar situations and locations, and come up with two or three likely candidates for planting. It gets more difficult, though, when the situation is new or the proposed species is one we haven’t worked with in that area before. That’s when we need to check our reference books or do some research online. Many reference books, however, don’t provide information like drought resistance or the mature size of the tree. A good reference that does is Plants for Tropical Landscapes by Fred Rauch and Paul Weissich. A designer may also contact a landscape maintenance company or an arborist to check if there are maintenance problems with a particular species, such as brittle wood or poor branch structure.

             New construction can be more challenging, particularly regarding soil characteristics. The landscape architect may be expected to complete his or her design before construction commences and many changes can occur during construction. The top layer of soil is usually stripped from the site during clear and grub operations, and if the site calls for fill the source is generally left up to the contractor. For these projects, specifying trees that can tolerate a broad range of conditions may be the most practical option.

 As far as soil analysis goes,Hawaii has 11 of the 12 soil orders so our soil maps are rather complicated. To add another wrinkle, there can be imported topsoil – possibly from different sources. When things get complicated, it’s best to check with the University of Hawaii or hire an agronomist. In most situations, using native onsite soils and amending them if necessary is better for the tree than importing topsoil from another source. 

There are some major “wrong tree, wrong place” issues with this young monkeypod. It’s planted just a few feet from the curb and utilities (transformer, underground electrical ducts) and the planter is too small for the mature size of the tree. Monkeypod trees grow rapidly and the trunk can reach seven feet in diameter. The root flare extends much further than that. Root pruning is not an option in this case because the conflicts are too close to the trunk. This tree was probably selected to grow rapidly to provide shade in a hot part of Oahu without considering maintenance issues. It will likely have a short life.

Utility conflicts are a common problem in many projects. The landscaping design should always be checked against the various site utilities. It’s easier and cheaper to move something on the computer rather than after it’s been built or planted. Of course, not all tree/utility conflicts are the designer’s fault. I have seen utilities constructed in places other than where they were designed – often because someone else took that subcontractor’s space. As the last one on the site, the landscape subcontractor can be left with trying to squeeze in the required trees anywhere he can, regardless of the design and long term maintenance implications. This is particularly common in condominium projects and other tight jobsites. Unfortunately, the end owner is the one who pays in increased maintenance costs and the trees usually come out on the losing end. Ultimately, the environment suffers through reduced canopy cover in our urban forest.

 We all know that trees grow, so the next time you are about to plant a tree, whether designing, constructing, or replacing, please think about what it needs to be the right tree in the right place for a long, healthy life.

This article was funded in part by Kaulunani, an Urban & Community Forestry Program of the DLNR Division of Forestry and Wildlife and the USDA Forest Service.

Selecting the right tree was published in the February-March 2012 issue of Landscape Hawaii, an industry magazine.