Choosing Trees for Larger Public Landscapes (and your yard!)

Still one of my favorite Oak photos. This one take in the late afternoon beneath a canopy of Interior Live Oak (I think) at Shiloh Ranch Park, last March.

Still one of my favorite Oak photos. This one take in the late afternoon beneath a canopy of Interior Live Oak (I think) at Shiloh Ranch RegionalPark, near Windsor, CA, last March.

A friend recently asked me if I had some favorite trees that I would recommend for planting on school landscapes, that would be like asking if I had favorite park trees, no I don’t…and I don’t have a list of proven performers either. A planting site being located at a school, only tells me something about the uses/abuses one can likely expect on a site, and nothing more. When we choose plants we need to be paying attention to a lot more than that. Many people are intimidated when it comes to choosing trees, there are so many and potentially, they live so long, growing from year to year…all of this tends to magnify the ‘weight’ of our decision.  People often look for short cuts because there are so many things to keep in mind when choosing. There are two major questions that need consideration first, the site conditions and design, what will the tree have to put up with and what do you expect?

I have written elsewhere about site conditions and the absolute necessity that our work be in concert with them. It has been one of our biggest mistakes to ignore these, a mistake that we continue to make. There are books written on this. There are ecologists who have spent their whole careers studying one particular place. Climate and the pattern of weather as it plays out on the ground; aspect, or the direction a site ‘faces’; slope which effects everything from the soil there and its temperature, to runoff, to human use and solar insolation; light in terms of sun and shade; exposure in terms of a site’s protections from extremes locally; the plant community that occupies it now and what will be there when your work is finished; what kind of cultural care it will receive from irrigation, to pesticide use to general management; drainage, soil type and structure, the keystone element in any landscape; the history of ‘disturbance’ on a site; it’s human uses over time; and, the expected future use once the new landscape is in. All of this is important to our decisions involving plant/tree choice. Many of these things are ‘fixed’ and in effect on a given site no matter what we may do. Others are entirely dependent upon our choices. The uses of the site, in this case as a school, will bring with it serious compaction issues. Others are more of a result of district policies and practices such as the aforementioned irrigation and pesticide use, while others will vary depending upon design questions and the particular plant community created, are areas protected or shielded from compaction, will this be a more complex, layered landscape or the more common ‘Grass and Trees’ landscape that predominates in typical park, school, public landscapes? Every choice matters, even the choice to exclude the school landscape from the children’s education. Such exclusions teach students that they are only background, secondary, because this is how society treats them. This makes schools particularly ‘hard’ on their landscapes.

Then there are issues of design, intent and expectation. What do we expect out of these trees and plants in this landscape? Are you simply filling space with trees? Increasing tree canopy? Then your choice is easier…pick any tree that fulfills the site’s conditions! If you have other aesthetic criteria or other purposes you want to fulfill, what are they? Are you trying to extend wildlife corridors? Or, is your intent more human and you want to create a landscape that, overall works to provide multi-season interest to the community and students? Are your goals that the resulting landscape be more sustainable in terms of the resources that it will require to maintain it a healthy condition over time? Will this be a lawn area that will be irrigated and mown? Will it be under-planted with shrubs, forbs and grasses? Are the plantings adjacent to play areas or sports fields? Is it likely to be cross-cut with informal paths? For desire design elements to be successful you must address site conditions.

A recommended list can be very helpful, if you still do your ‘homework’. It will also have at least two other effects: it will narrow the selection of trees that we consider down from many thousands of species and varieties to a handful decreasing the likelihood of a ‘good fit’ and secondly, it will encourage growers, especially growers of larger caliper trees, which are typically required by code to be planted on streets and for public projects, to grow only those, further reducing the choices of those who are looking for something different. I cannot ‘blame’ nurseries for doing this as they have to put in a considerable effort in terms of time and resources to grow trees. The larger the tree the greater the commitment and nurseries have only so much to give. They can ill afford spending 4, 5 or more years growing something and, not able to sell it, discard it. Crops with a quicker turnover, have less invested in them.  I am reluctant to make a list.  That some would reject it bothers me less than that others might rely on it too heavily and ignore the process of choosing trees by ignoring their sites.  “Oh, they recommend ‘Acer blah blah’.  The garden center has six of them.  Lets take this one.” And, then the tree is planted where it shouldn’t be.  No list will ever anticipate all of the possible bad decisions.  Even if plants are goof or bulletproof, they still may not be good choices.  Lists should be made for each project,  Each choice qualified given all of the above.

Many people use their local garden center like a catalog. They visit, see what’s available and make a choice. Ultimately we all do this unless we are working on a large project, that requires a large number of plants putting us into the position of securing these in advance of our actual on-site need for them. We have them contract grown or get written commitments from several growers in advance or maybe even buy them early and pay to have them ‘held’. Designers and contractors will often use ‘brokers’ to find what they are looking for from nurseries across the region. Brokers may have knowledge or relationships in the industry that give them a better chance of finding and securing the specified plants. Remember that not only is the variety of selections limited, but so to are the numbers. A manufacture cannot gear up and crank out more on demand.

What all of this means is if you want plants best suited for your site conditions and able to meet your design expectation, you must act with some forethought, keeping in mind the ‘industry’s’ limitations and annual cycles, by not waiting to the ‘last minute’ to choose/search; widen your list of suppliers/growers; be willing to use plants of a smaller more available size; and, write your plant specs broadly, but with enough specificity that your choices will meet your most essential site and design ‘needs’. If you simply choose a tree and then can’t find it in the size you need, you may find yourself in panic mode and make a poor choice. Don’t go looking, e.g., for a 3 ½” ca. Pterocarya fraxinifolia: round headed, fast growing (to 2’/year) large, shade/nut tree to 60’+or- with late spring catkins hanging to 20”, course compound leaves to 2’, yellow fall color; drought tolerant though prefers some summer water (found by rivers in Iran), full sun, little used in the Pacific Northwest, so few examples. So, what do you do if this is your choice and you can’t find it? Keep searching and wait another year? Could that be an option? This is why many people often look only to availability lists and make their choice from them. Give yourself a well-defined range to work within, one that will give you the greatest chance of being happy with your result. If you are simply looking for shade tree that grows to 60’, fairly quickly, that is tolerant of drought, but ought to be accepting of summer water, as in irrigated turf, will take full sun and exposure to area cold…there could be many choices. If you want it to not just ‘survive’, but do well, you need to look around the region for examples growing under the same conditions that your site will offer it. Such lists would be very helpful to those who lack experience choosing trees and could be derived from inventories maintained by Friends of Trees or Urban Forestry of Portland Parks. This could be a very valuable service.

It would be great if we could sit down at our computers and enter all of the site requirements and the specs for our selections and have it spit out a current availability list and rank substitutes by how well they meet our criteria, but there is no such thing. That’s why many designers, landscape architects and contractors tend to stick to a narrow list of trees for their designs or rely on plant brokers, who have relationships with growers and do this every day. Of course if you are only looking for a couple of specimen and your size criteria is flexible down to quite small, your choices balloon immensely.   Creating a designer’s or collector’s garden is very different than a public landscape. These large landscapes tend to be ‘built’ quickly and completed while the others are an ongoing process, labors of love, tweaking and adjusting. Those that are put in ‘all at once’ tend to be more expensive per square foot than most public landscapes. In any case it is important to be in tune with site conditions and to make plant choices that are supportive of the design and its theme.

Okay, after having said all of this, do I have favorite trees, of course I do! They walk the line between being perfectly suited to site conditions and gorgeous ornamentals with remarkable season interest, often multi-season interest, but are almost always trees with beautiful, elegant, branching structure…and of course there are exceptions, even to that. Landscapes should be beautiful! A utilitarian landscape, ultimately, is unloved. Native landscapes don’t earn ‘brownie’ points simply for containing native plants. Are they successful? Do they grow with vigor? Do they contain the elements of complexity that healthy native landscapes do? Are they expressions of healthy complex relationships or are they struggling, limited constructions, too simple to exhibit the health and vitality they should? Landscapes should teach us about beauty, its complexity and simplicity. Beauty is about the relationship between the many plants and they way that they occupy their place. It is internal and evolving.

I am developing a thing for Oaks. There are an estimated nearly 600 Oak species worldwide. Few naturally extend into Oregon. 18 occupy California. Many more extend well into the SW US and the mountains of northern Mexico. Many are being found to be adaptable to urban conditions in the Portland area and well suited to our winter wet/summer dry weather, generally accepting of little to no summer irrigation. Other species, native to mediterranean climates similar to ours, deserve some searching out. Some are in fact ‘intolerant’ to summer irrigation. As such they can be perfect choices for ‘sustainable’ landscapes. Of course this does not mean they will be successful everywhere. Cistus, Sean Hogan, has been pushing these hard to his clients, successfully, and to the City Forester, much less so. That is a whole other issue. Other small nurseries are offering more of these Quercus species every year. Seven Oaks Native Nursery. Heritage Seedlings. Desert Northwest. Xera. There are many interesting Oaks out there, however, do not think that an Oak is an Oak. Many nurseries in Oregon, understandably, want to crank out product as fast as they can so they choose material that grows quickly for them. Pin Oak, Northern Red Oak and Scarlet Oak all grow fast in the Pacific Northwest. These and others all grow large quickly here and will soon over whelm the typical urban landscape. They also have persistent leaves only dropping them slowly over the course of the winter. The Oaks that I recommend, like our own beautiful Quercus garryana, or Oregon White oak, are slow growing and long lived. This goes back to your selections and how nurseries operate. I will leave it at, availability does not equate to suitability or desirability. So, I like a lot of Oaks.

There are also a few trees that I have found very well adapted to conditions I would often find in Parks. Because I worked for many years in the Downtown area with its horrendous soil conditions, think very compacted, poorly drained and relatively shallow due to years of grading, filling and urbanization, I almost always found Nyssa sylvatica, Tupelo, to be an excellent performer. The same for Metaseqouia glyptostroboides, Dawn Redwood. Conversely, there are many, especially under the conditions that I had, that virtually never performed adequately. Among these are many of the Prunus serrulata cultivars that suffer severely in heavy wet winter soils especially when in summer they are then subjected to summer irrigation out in the turf. In my experience they live a few years until performing a long slow slide into death. Yet people keep planting them, which would be okay if they made more effort to seriously modify the growing conditions. I didn’t plant them. I also rarely ever planted Cercidiphyllum japonica, the Katsura Tree. I love these. Unfortunately so do landscape architects who seem to spec them in without regard to site conditions. These are a native of mixed Japanese woodlands not parking lots, compacted thin soil surrounded by acres of reflective hard surfaces. These all struggle when planted poorly. I’m tired of looking at them.

I am also tired of having choices limited by an available palette of plants that is actually intended for back East and the Mid-West, the largest share of the market that regional nurseries grow for. The Oregon/Willamette Valley market is simply too small for the big growers to bother with. We get the left-overs. If you want plants that are better suited to the particularities of where we live, you have to seek out the many smaller growers. But this is the reality today. The bulk of what is grown here is for colder climates that receive summer rainfall. So, we plant ‘Patmore Ash’ just as they do in Pennsylvannia where the species from which this is selected, normally grows. Landscape Architects use the same palette here. Large growers in California do a similar thing only, because they have such a huge resident population, their growers cater to their more specific requirements. California residents, architects and contractors have a much wider array of plants attuned to their climate than we do. Spend any time down there and you can see it playing out across local landscapes. But, not here. Most of our Ash, Maple and Oaks are suited for the growing conditions of the mid-west and East. Historically, and the choices are broadening slowly, some growers have been catering to the demand for native plant material on large public projects and these have often been grown on contract. This has been slowly changing as the market has been expanding allowing growers to grow more natives on speculation that buyers will come and not leave them holding ‘over-mature’ product. Plants can’t be warehoused until there is increased demand. They have to be moved or disposed of. This problem of availability too often drives design. Good design, good plant choices, can’t be made when availability limits you to mediocre choices, choices that will work, but….

As gardeners and clients become more sophisticated they will put more demands on local suppliers and growers. Smaller niche growers will start filling the demand until it becomes more profitable for larger wholesale growers to jump in. It is the nature of the beast. So, for now the best choices are not automatic. Buyers seeing a preponderance of ill suited tree choices won’t know and will buy them. These will often struggle, languish and decline relatively quickly, especially so on highly disturbed urban sites where poor rooting, shallow compacted soils amplify the shortcomings of the generally available plant material.

Public programs really should be advocating for the supply of appropriate plant material. Preaching ‘right plant right place’ and then ‘under’ delivering on plant material is doing us all a disservice and undermining the credibility of the industry. All trees are not created equal and this summer has driven this fact home as I go down the streets seeing all of the trees limping along, defoliating early, many exhibiting the die-back characteristic to trees from summer rain regions planted here in our summer dry conditions, as I said, amplified by restricted root zones common on compacted sites often wedged in between buildings and streets. We can do better. People need to step up!

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