Planting Trees Under Trees

More is better in some cases, and in others it’s not. When it comes to planting trees, more is almost always better. If your facility or customers could use a few more trees, think about one of the most commonly overlooked areas for siting sturdy trees: under other ones. Be especially mindful of the factors that make up the theme of right plant, right place when delving into the tree-under-tree endeavor.

Replicate Mother Nature

One of the main reasons for placing small trees under large ones is that Mother Nature does it. Small trees can serve the landscape well when placed under larger specimens. Again, this is the way that Mother Nature creates landscapes, with understory trees popping up in layers under larger trees. A healthy, sustainable landscape would normally contain large shade or framing trees; medium-sized trees well placed for color and interest; small trees under them for shape, color, texture and form appeal; and ground plane plants such as perennials, ground covers and turfgrasses. Once the layered landscape is developed, it provides beauty and function.

In addition to using small trees for layering, consider them to accent important features of the landscape. Because entrance areas are not always obvious in every setting, you may want to highlight building entrances, driveways and important paths by locating small trees nearby. This helps to focus attention on places where you want people to go or look.

Mother Nature is a good teacher in other tree care areas as well, such as mulching and planting trees from seed. The “stuff” that falls from trees — seeds, leaves, cones, needles, fruits, bud sheaths — creates an excellent natural mulch and should be allowed to accumulate to encourage root growth and expansion. Likewise, tree seeds that germinate develop healthier root systems than ones that are grown in nurseries for several years. Trees grown in nature develop root systems without pot-induced girdling roots and soil interface problems; in many ways, Mother Nature is a good teacher and role model.

Mother Nature landscapes by placing trees under trees and creating depth. Photo: John Fech

Create depth in the golf course landscape

Golf courses, especially smaller facilities without an arborist on staff, can be a good customer and a significant income stream for qualified arborists. Because trees serve several functions on the golf course, care must be taken to identify and validate the purpose and placement of each one. First and foremost, trees serve to define the sides of the fairway. Any landscape space needs enclosure and enframement at some level, and the golf course is no exception. Depending on the level of maintenance of the course, the rough can be at various levels; normally from 2 to 6 inches. The lower the height of cut of the rough, the more trees and shrubs are needed to mark the fairway, providing a target for the golfer. In many cases, mature trees exist with no understory in place.

Tree placement that helps to define the fairway may have several approaches. The “layered” or “tiered” look can be effective, with small to medium-sized shrubs located in the first cut of rough, larger shrubs behind those, with trees of various sizes as a background to the shrubs. Alternatively, masses of small trees intermingled with larger ones can be planted in the deep rough to provide a sharp mass/void feature. This can be quite powerful, creating interest and functional appeal to the golfer.

Other good locations for trees under trees

Just about anywhere except where space is limited — home landscapes, corporate headquarters, city parks, recreation areas — is a good location for incorporating smaller trees under mature ones. The key phrase is “except where space is limited.” If room for adequate rootzone expansion exists, approaching clients with suggested plantings makes good sense.

On the other hand, shopping malls, parking lots, gas stations and along city streets are usually not the best locations for trees under trees and, actually, may not be prime locations for any trees. If space is limited, large and small shrubs, perennial flowers and ground covers are usually better choices than trees.

Placing trees under trees provides many benefits. Photo: John Fech

Site analysis

The best place to start with any planting project is with an accurate base map. The base map provides all necessary information regarding the permanent features of the area to be enhanced, including property lines, easements, building footprints, utility locations, contours and existing plants. A north arrow and graphic scale must be included to provide reference when communicating the eventual design to customers and to retain accurate space relationships if the finished plan is reduced or enlarged.

The overall design concept of incorporating smaller trees under mature ones will dictate the program. Program components quite simply are a listing of wants and desires of the stakeholders of a project. Early on in the design process, they tend to be general. A typical program statement for these types of enhancements would include such things as minimized turf areas, creation of ornamental beds containing fall color and spring blooms, screening, etc. Specific plants are chosen at the end of the design process, not the beginning.

The next step is a site inventory/analysis. This is best performed on site, gathering information, taking notes, and gaining a “sense of place” in the landscape space. The inventory is first, identification of problem areas as well as the assets of an area. Use a piece of tracing paper and lay it over the base map. This provides for accurate note taking and documentation of potential concerns or opportunities for features. You may want to photograph the area for future reference and comparison. If the finished design turns out well, you may want to use the before and after photos to sell a job to another customer. The analysis comes later, an evaluation of the importance of each specific condition. The soils, neighboring views and existing buildings may be only a slight concern, but the slope and prevailing winds may be major contentions.

A bubble diagram should be drawn after the program is in place and the site is analyzed. This will help put the written word into a visual format. Again, working on tracing paper over the base map, diagram the site according to function. Traffic flow, high-use areas, low-use areas, water features, etc., are all components that should be drawn in at this point. Exacting detail is not necessary in a bubble diagram; rather, circles and ovals with a light colored shade will suffice. Concept drawings are then developed, combining the program considerations with the site analysis information and the original design concept.

Site assessment/analysis creates business as well as prevents it. The opportunity to replace severe or moderately pest-susceptible specimens is a good one in that it creates voids that must be filled with better-adapted plant material. That’s one obvious source of income; another is the need for future inspections and analysis, which should not be gratis. Inspections are an important arboricultural and grounds maintenance function and should be profited from accordingly.

As long as the rootzone is adequate, small trees can be incorporated.
Photo: John Fech

Tree selection criteria

After the site analysis is complete, consideration of general and specific issues related to the trees under trees concept can begin. Many issues should be considered and are not limited to the following:

Shade tolerance — Because the new tree will be located under a taller one, it’s a given that partial to heavy shade will be present. Monitor the site at various times of the day to determine whether light shade, dappled shade or heavy shade characterizes the site.

Size — In many landscapes, the lower branches of mature trees have been limbed up to create an unnatural openness. While plant selection for trees under trees is not akin to placing pieces of a jigsaw puzzle in place, there is a certain element of choosing based on eventual tree size for all specimens involved.

Rootzone allowance — As mentioned before, adequate root zone allowance is crucial to the success of the enhanced landscape and should not be overlooked.

Disease resistance — Due to the canopy effect of the mature trees and possibly the nearby smaller trees, wind speeds through the modified landscape are likely to be less than the previous condition. Be sure that the specimens chosen are resistant to periodic leaf wetness and a variety of foliar pathogens.

Fall color, bloom sequence — One significant selling point to incorporating smaller trees under larger ones is the opportunity to infuse color and texture into a monochromatic or overly simplistic landscape.

Editor’s note: This article was originally published September 2011 and has been updated.

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