Evaluating Your Garden Site

Perhaps the most important question any gardener can ask is, “Where do I garden.” While this may not be as sexy as choosing the plants we’ve always wanted or re-creating a spectacular garden we’ve seen, it is absolutely essential over the long term for the health and success of your garden or landscape. While we can stray from the limitations of our sites, it will cost us. So it is still important to know our sites, to make the necessary modifications whether they be protection from winter winds, improving soil drainage to whether or not we will even need to irrigate, how often and how long. If you go to considerable expense to install your landscape and it fails to meet your expectations, you will need to re-evaluate either your site, your expectations or both.

There is more to gardening than locating yourself on the Sunset zone map and simply plugging in plants, though this is where many of us start. Let’s look at my garden. I garden in inner southeast Portland, somewhat of a ‘banana belt’ compared to areas to my north and east where the winter Gorge winds can be severe, or over on the west side where the surrounding hills can hold cold air. I have not been keeping weather records, but I understand that my area can average 10” or more precipitation annually above what the airport receives (or official reporting site). Downtown has more of a heat island effect raising low temperatures just enough for me to notice that the same plant, downtown, emerges and flowers a week, +or-, before mine does. Coming into the fall frost tended to nail my Coleus before those in my old display beds downtown would. In my 25 years at this site, I cannot recall a single digit low, putting my site somewhere around an 8a or 8b.

A significant limiting factor is my soil especially when considering our winter precipitation. I have a heavy clay loam that can open up ½” and ¾” cracks during the dry months of July and August. It is deep and drains relatively slowly. Many warm season plants, particularly more southern and sub-tropical bulbs, such as many of the Crinums, Hippeastrum as well as Taros can rot out for me even in a not particularly cold, for us, winter. Many warm season plants simply don’t tolerate our cool wet winter soils with the fungi that populate them. Compost alone over the years helps with this problem only marginally. When re-working a bed for the last several years I have been adding an inch or more of pumice, ¼-12 gravel, can be used, but I tend to stay away from it because I don’t want to bucket it up my stairs to the back garden. While I do routinely add compost my soil has an overall low organic component with a nearly non-existent humus layer making this area difficult for most but the toughest woodlanders.

My site slopes to the west approximately 4-5% not enough for much of the precipitation to move off site. Along the south property line, because of the cut to accommodate the street, the slope is much steeper, one section is held behind a two stepped concrete retaining wall, another simply slopes to the sidewalk while the east side is held by a low railroad tie wall. These edge sites in my garden, especially near the break and the slopes themselves, are drained well enough to support Agave parryii, Beschorneria, Hesperaloe and Zauschneria without significant amendments while the toe of the slope, where winter wet tends to sit, can be quite wet even into early summer.IMG_0319

The south facing slope adjacent to my stairs combines this with enough protection from my house to be a successful site for a quite happy Butia capitata, or Jelly Palm, that came through last winter unscathed with no additional winter protection.

With the western aspect my back garden can be very hot in the summer. There are no large shade trees. A 25 year old Parrotia and a three 15’-ish Trachycarpus cast what shade there is. Our house provides the expected shade to the east and west, morning and afternoon. Our bamboo and steel ‘Pavillion’ provides some shade to its immediate area as does a small Kousa Dogwood on the northern edge.

My entire garden is zoned for drip irrigation that works quite well. Only the back garden receives regular water. My street facing garden, I live on a SE facing corner, receives enough to establish new plantings and an occasional desert monsoonal soaking to keep things looking their best.

Wildlife damage is minimal other than the occasional pot toppled by a raccoon, squirrels planting Walnuts and of course neighborhood cats stalking birds and various other desirable fauna. Mole or vole damage is minimal to none though something seems to have gotten a couple of my Dahlias(?). Our son is no longer a factor in terms of accidental damage and we have clearly delineated social areas to contain friends and gatherings. All of these can be limiting factors in terms of plant choices in the garden.

As much as I may want to try a Holboellia angustifolia or one of the Schizophragma on one of my Trachycarpus’ trunks, it is probably not a wise decision. They will simply get too much sun and the Palms probably aren’t an adequate structure to support them over time. Had I more shade and a bigger tree to grow them up…but, then it would be a different garden.

Each garden or landscape will present differently with more shade or coarser more quickly draining soils, or it may lie in a cold air pocket bringing lower average winter temperatures. Another, more subject to freezing rain than mine, should give the gardener pause when considering trees susceptible to damage by ice. There is little a gardener can do if its simply too cold to grow what you want short of digging up said plants every winter and protecting them indoors, building a dome over your garden, planting new every spring or simply moving. If you have already taken root in a place you’re left with understanding and making better plant choices for your garden and doing what you can to improving the growing conditions for the plants you choose to grow. To make these choices you have to know the requirements of the plants under consideration.

Plants evolved in specific places with relatively stable conditions over thousands and even millions of years. If you are going to try them in less than ideal conditions you need to be aware of this and do what you can to ameliorate them. You need to know what you can get away with.

Evaluate your garden site: Climate type – cooler mediterranean; 40”-50” precipitation; Growing Zone – 8a, down to 10 deg. F; Soil type – clay loam, slow draining, low organic content, slightly acid; Overall Slope – 3-5% Aspect – predominately west

Define the distinct areas within your garden/landscape…the micro-sites as these can vary widely.

  • Sun-shade exposure
  • Presence or absence of aggressive tree roots, some trees have much more aggressive roots, e.g., Norway Maples, Beech and Elms
  • Heavy litter drop from existing trees, e.g., Sequoiadendron, that can bury many plants
  • Established evergreen trees and large shrubs that tend to keep an area drier beneath them by ‘shedding’ rain and through transpiration
  • Distinct changes in slope, e.g., wet spots, hot dry spots
  • Beds or pockets of modified soil especially where drainage is different, e.g., ponds and bog gardens, berms, rock gardens or walls
  • Existing plant material, especially strong growers, that must be accommodated
  • Places previously built on that have had soil compacted to stabilize it
  • Buried construction debris including gravel base material from adjacent hard surfaces, slabs and footings
  • Compaction/ poor drainage from new construction
  • The presence of fill soils on heavily ‘disturbed’ sites
  • Perennial weeds, established, especially strong growing persistent weeds, e.g., Horsetail, Bindweed, Clematis vitalba, Canada Thistle and Quackgrass
  • Annual weeds that are strong growers and prodigious seeders like various Brome grasses

One of the most helpful things a gardener can pay attention to are the plants doing well on your site already. Plants don’t play mind games with you. If Cyclamen has naturalized across an area of your garden that speaks to the conditions there and unless you’re completely committed to creating a bog garden full of Darlingtonia, as an example, you should seriously consider what your site is telling you. Look to the plants that are doing well. I have given up on most of the woodland bulbs as most of those I’ve tried in years past have declined and died. If you want to grow something do what is needed to get the site conditions more in line, berm the soil and add grit if the crowns need to be drier through winter. Add lime to neutralize your soil if you are tired of your blue Hydrangeas, assuming that they are a type that flowers red in alkaline soils. Consider the expense of building a raised crevice garden if you want to be successful with Agaves on a mostly flat site. Simply throwing plants at a site is expensive and discouraging. And,…always be open to letting go of your plant theme. Some things may simply not be possible on your site. It is better first to consider the possibilities most amenable to your site. Most of us aren’t made of money and if our gardens become a constant battle to maintain, we will grow discouraged.

Gardens are a process that evolve over time. They do not have a fixed end point. All of these things and more are factors when choosing plants for a landscape. Unfortunately our knowledge will never be perfect. On the other hand, most plants will tolerate a range of conditions. There is some degree of forgiveness or no one would garden and the earth would be a barren place. It is to our advantage, however, to garden with both eyes open and our attention focused.

You can use the conditions your site offers as a screen for plant selection knowing that there is some latitude if you are willing to make ‘adjustments’ to accommodate the needs of the plant and place plants with similar needs together. A hodge-podge of plants with conflicting requirements is a recipe for catastrophic disaster. You cannot make a garden successful simply through force of will.

So, if I pay attention to my own advice, I would select plants from mediterranean regions of the world, like the west coast of North America, hardy to zone 8a or colder, preferring slight acid clay loam, that tends to be wet in winter, such as plants that were once found in the Willamette Valley prairies or Oak Savannah. Mine is not a wooded site so woodland perennials and understory plants won’t be a good choice and they haven’t been, generally declining and disappearing relatively quickly. My neighborhood is older, inner southeast Portland, built before the common use of heavy duty grading equipment so it is likely that my mineral topsoil is native to this site. But there are two ‘cuts’, one along the south property line and one on the west that will tend to dry these areas out more quickly and I take advantage of them.

I try to follow a few ‘rules’ when I’m buying plants, but I am weak, still, the larger a plant’s ultimate size and/or the more expensive it is to purchase, the better I am about following my rules. I go with a specific list and, secondarily with the specific holes in my garden in mind or of the plants I want to replace. As much as I wanted to get one I didn’t buy a Schefflera taiwania. I already have S. delavayi and I simply don’t have the protected, shaded place for another. Still, I was looking for another evergreen that wouldn’t overwhelm the space and I liked the idea of the finer texture of the S. taiwania. That’s why I was looking at the Holboellia angustifolia. That’s when I saw another Arailia family member, Metapanax delavayi, a plant with the characteristics I was looking for that I think I can live with longer term. All of the plant stars seemed to line up. Since I irrigate this area anyway it should be a good fit. I am a bit too much of a collector for my garden’s own good…so I bought it, planted it and now we’ll see. IMG_0318-1These Araila are not mediterranean. They come from a monsoonal climate in Asia. The Trachycarpus it is planted beneath should help keep it drier in the winter and my irrigation in the summer should accommodate its needs. I think I have temperature and light covered. It’s bed mates have similar requirements or have at least demonstrated a tolerance to these conditions.

Each time a plant dies, which happens all too frequently even now, I make a note. Embarassingly, sometimes it happens simply because I missed a watering or two in summer while a plant was still in its pot. Other times I might forget about it when a neighbor overgrows it and it spends a season weakening in the dense shade of the heavy overtopping growth…and then there is the errant spade slice through a dormant bulb that sets it up for rotting. That’s what we do while we’re gardening, when we’re not drooling over the beauty of our work, or worrying about what comes next, we observe and consider. It does no good to jump to conclusions, to assume things not in evidence. Our gardens teach us about the relationships our plants share and such an education opens our eyes to the world around us, because it is no different there.

Plants naturally ‘choose’ their sites, but they do this by seeding and growth from surrounding soils, not conscious choice. Our gardens, our ‘disturbed’ sites, do not have a repository of preferred seed and plant material waiting at the ready. They have us, and a landscape, filled to overflowing with seed and plants brought here and ready to move where they can. It is up to us to make the choices now for what was once a more or less automatic process. To do this well we need to understand our landscape, its soil, the movement of water on and through it, all of the energies at work, the nutrient cycling and all of the plant and animal players to make the best decision given our goals. We will always make mistakes, but as long as we care and we pay attention we will make better decisions and our involvement will become more integrated. As thinking and aware ‘animals’ our roles are larger.

When we’re kids we are taught that we are responsible for our actions, there are consequences, and often times, fair or not, we suffer the consequences of those who came before us. We don’t get a clean slate. We simply move ahead. We’ve run out of virgin unspoiled wilderness. It’s time to put up or shut up. So what if your garden is infested with Canada Thistle…what are you going to do about it? There are no whiners allowed in gardening. But that’s okay. It keeps the work interesting. If it were easy anybody could do it and where would be the satisfaction?


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