Friday, July 8, 2011

Beyond the Border Part 2: Massing Matters

The same rules that create impact and drama in art can be applied to perennial planting.
My last post set up my proposition that perennials and grasses—the most dynamic plants a gardener can use—ought to not only be used more often, but used in as a larger percentage of our built landscapes.  It’s time to liberate perennials from the confines of the British border and embrace a new aesthetic inspired by the patterns and palettes of our native vegetation. 
This post will ground my lofty rhetoric with some practical how-to advice.  How do you design for long term success with plant material that is inherently ephemeral?    To achieve lasting, low-maintenance perennial gardens, there are two areas one must master: composition and plant selection.  This post will focus on the first, and most important, rule of composition: massing.
First, let’s understand the context we’re discussing.  Perennials in a landscape setting (parks, civic landscapes, large residential) are inherently different than a flower border.  They are larger in area, typically set farther away from the viewer, and are not gardened as intensively.  So the rules of composition must address this context.
Massing Matters
More than any other strategy, massing perennials and grasses together is the golden rule for landscape perennials.  Why?  We group several of the same plants together in order to make them more legible and give them visual impact.  A single flower in a half-acre planting disappears; but a block of 100 (residential), 200 (small park), or 500 (large park) has dramatic impact even from a distance.  Massing perennials together draws attention to their ornamental characteristics.   It amplifies their color, form, and texture.   More importantly, it also helps relate the scale of the plantings to the scale of a house, building, or park.  A mass of 20 Echinaceas, for example, can look paltry next to a monumental building. Massing plants together gives the planting proper proportions to their context.
Larger massings of sedges and perennials in a biofiltration garden for an office park.  The lines between the species create a pleasing composition.  Design by Ed Hamm for Rhodeside & Harwell. Photo by Thomas Rainer.
The European ‘New Wave’ style made popular by designers like Piet Oudolf, Noel Kingsbury, Michael King, and other celebrated designers tends to interplant perennials in smaller clusters to create highly textured tapestries.  I am personally a huge fan of this look, particularly to see it executed on large public projects like the Highline and Lurie Garden in Chicago (even Oudolf masses plants together for effect).  These designers use repetition rather than massing to give their compositions visual coherence. However, in my experience, the main drawback of a mixed meadow approach is that it requires quite a bit of maintenance, particularly in the heat and humidity of the eastern U.S. 
Massing reduces maintenance.  By placing plants of the same species together, you group them by their cultural requirements.  Everything within that block needs the same care.  It also makes weeds much easier to identify.  In highly mixed plantings, identifying a weed from a young perennial or grass requires a trained gardener—a luxury not available in most landscape settings.  Massing also makes it easy to re-plant if a perennial dies or struggles.  Every project I’ve ever worked on required re-planting anywhere from 3-10% after the first year or two.  With large masses, it’s very clear what needs to be replanted. 
A nicely interplanted moment, but with five species in just a few square feet, the perennials are already competing for light and nutrients.  To keep this composition together would require quite a bit of  maintenance.
Massing plants of the same species together also reduces competition between perennials.  Any time you mix species, the plants compete for light, water, and nutrients.  All of my early experiments with interplanting perennials went poorly as one plant often “ate” another.  The composition grew together, the more aggressive plants eliminated their more demure counterparts, and the end result was a total mess.  On one project where I interplanted about ½ acre of perennials, I went back a year after it was installed and had to un-interplant the entire garden.  The garden had grown together in this awful mess.  Anything that was mixed together was pulled out and separated.  The correction worked.  I’ve visited it several times in year two, three, and four.  The masses are more readable, the maintenance staff can easily identify weed from desired plan, and the garden is more stable. 
Since then I’ve had a good bit more success with interplanting perennials, but it requires much more planning, horticultural knowledge, and care with plant selection than I initially understood.  I’ll discuss some simpler strategies for interplanting later.  Even though I interplant quite a bit now, it is still within the context of larger masses. 
Two images of a garden designed by Wolfgang Oehme that feature large
perennial masses appropriately scaled for the residential setting.
My early mentor, Wolfgang Oehme, of the design firm Oehme, van Sweden & Associates is a huge proponent of large-scale massing.  Wolfgang is one of the great plantsmen of the last century, and his success in using this richly layered style of large perennial masses validates this method.  Since I’ve left OvS, I’ve had an opportunity to experiment with refinements to this style, particularly a method of matrix planting.  It blends all of the advantages of large masses (maintenance, legibility) with a more visually dynamic field.  More on that later.Next post: What type of perennials and grasses do I choose?  Some tips on choosing worthy plants for landscape settings. 


  1. Great series you're doing. I look forward to your book. Man, are you right about mixed planting, which I do. You have to know your plants and their behavior very well. One big mistake I'm dealing with (or not dealing with; thinking about how to deal with) is Spartina pectinata, which should be planted in isolation. It does grow into the other plants and makes a real mess. (Love the Frankenthaler analogy.)

  2. This has been the real breakthrough for me--an amateur trying to build a garden. With massing, I can now enjoy the impact of color from inside my house as well as in the garden, and maintenance is so much easier!

  3. I love the look of massing plants; however, I wonder about year round interest. Won't you only have a week or two when each mass will be in bloom?

  4. Thomas, I don't see myself planting any big landscapes, but I'm finding this very interesting (and I'm a huge Helen Frankelthaler fan :-)) -Jean

  5. James,

    I couldn't agree more. Interplanting is hard to do well, but can be pretty spectacular if it works. You're garden is marvelous. It has a nice balance between legibility and intricacy. Thomas

  6. Katie,

    That's a great question. The short answer is that with the large massing landscape plantings I'm describing, each base plant essentially has to have year-round interest. That places quite a bit if pressure on plant selection. My next post I'll talk in more detail about what types of perennials and grasses work in this setting.

  7. Jean,

    Thanks for reading--even if you're not doing any large installations. Even on relatively small gardens, I think massing plants matters. It helps make a garden more legible, and it amplifies the spatial quality if a garden--creating a more serene and livable space. Thomas

  8. Thomas, I've been a huge fan of OvS forEVER, and had the good fortune to be with both James and Wolfgang on tours in the DC area during an APLD conference. (I even came home and created a pool surrounded by grasses like W.O.'s)For clients with large properties, I can successfully recreate their larger scale plantings, but in my own garden, which is only about 30 feet deep to the fence, I am having trouble making the massed plantings work effectively. Ideas?

  9. On my blog, I review a lot of books about garden design from the point of view of the lover of perennials. After several years of reading and reviewing practically everything that has been written about this subject, I began to wonder if anything new could be contributed to the ongoing dialogue. This series of post makes it clear that you are making a serious contribution to this body of knowledge, and I, for one, am grateful.

  10. Hi Mary Ann,

    I'm not sure what's not working in your garden. There are still a lot of factors that drive success or failure of plantings. Massing itself helps, but is certainly no cure-all. Certain species do better massed than others. Aster oblongifolius or Solidago 'Fireworks', fore example create these dense, wonderful masses, while other plants like Rudbeckia or Echinaceas don't hold together as well. It could also be soil, exposure, etc. My next post will focus on plant selection which is a huge factor in making them successful.

  11. Allan,

    Thanks for the kind words. I would love to compare notes with you one day. The rules for composing a beautiful perennial border (like the ones you do) are very different than for perennials in landscape settings. I'm curious if you've found good maintenance strategies for border-style plantings? If so, you should do a post on those.

    Of course, I'm always hesistant to perpetuate a myth of a no-maintenance garden. Maintenance is the heart of gardening. But there are certainly ways of planting that reduces it.

    By the way, your comment about perennials being the soul of the garden is wonderful. I've never thought of them that way, but I think you're right. I love a good shrub border, or tree allee, but there's something downright soulful about perennials in a garden. An astute observation from one of my favorite perennial artists.

  12. Good points given Thomas, agree on how much massing adds to a landscape when using perennials/grasses. gives the eye a good flow and packs a punch that you wouldn't get with one plant. didn't consider the fact that it reduces competition and calls for easier maintenance, by everything having same care and really sticking out weeds/unwanteds. Thanks

  13. Cameron PalmerJune 14, 2012 6:19 PM

    I agree about this topic. Massing really does matter when using perennials/grasses in a landscape. It is also good to know that massing will help make maintenace much easier as well as identifying and removing unwanted weeds. Thanks

  14. You are so right about all this massing. It's the one design decision you never regret, unless you choose the wrong (invasive) plants. Then it all turns to mush and requires much work. Massed plants look like "nature perfected." Wonderful blog, look forward to more.


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