Slope Aesthetics in San Diego from a Natural Perspective

San Diego is mainly a series of canyons and mesas, which means that many homeowners must contend with landscaping on slopes.  But while successfully designing and installing a landscape on a slope is a huge challenge, it is also a potentially rewarding one. The issues that arise in relation to this challenge range from the difficulty of working on the slope–digging, walking about on it, and maintenance–to safety considerations, irrigation, and aesthetics. Because of these challenges, this will be the first of a five-part series. In this first installment, I will address aesthetic considerations from a natural perspecive.

A great way to think of how natural landscapes relate to cultivated ones is as raw material to finished product. One needn’t, nor probably shouldn’t, try and reproduce the full look of a native slope (unless your interest is in habitat restoration), but rather echo the local ecosystems in the designed landscape. Another way of saying this is that the designed landscape refers to or indexes the native landscape, but also sets itself up as its own entity. This thinking is originally Japanese, but it fits in well with modern sensibilities perhaps more comfortably than other aesthetics.

To see what I am talking about consider the following photograph of a native hillside in San Diego in late October. Keep in mind that this is the San Diego ecosystem at the end of its dormancy, the period just before rains start, so the plants look a little ragged:

Many people who see such a photo, or who see San Diego’s hillsides in the summer and autumn would be hard-pressed to find an aesthetic to work with given the overabundance of weedy looking, dried, dead, and brown foliage. But there is a lot more to appreciate here than dormant perennials and grasses. For one thing, the rocks provide an outstanding feature in defining the flow and curvature of the slope. The slope, it turns out, is anything but uniform: it folds into something of a gully, and the rock helps to define that.

San Diego native slope with evergreen sugarbus

The other outstanding element is the sugar bush (rhus ovata) that punctuates the vista at regular intervals with its beautifully-shaped evergreen leaves. It rises up out of the dormant plants in neat rounded shapes. So these are two elements that can be imitated in slope design. One needn’t use sugarbush specifically to create this effect. Its size makes it impractical for most of us. But its regularity and spatial properties provide inspiration.

Above is a simplified view of how this principle might apply to a slope in a residential neighborhood:

Sugarbush is probably too big a shrub for most landscapes, but the pattern can be reproduced with any number of medium to small-sized evergreen shrubs, creating a look that fits in nicely with San Diego’s native slopes.

A final caveat:  the look as described above goes against the principles that are typically taught in landscape architecture, in which plants are grouped into masses.  But this is most likely the influence of ecosystems from more northern places than San Diego on design principles , such as those found in England, for instance, where plants tend to grow tighter.  But if one looks at gardening traditions further to the south, say, in Italy, or even further south, to Egypt, one starts to observe a much greater use of space and focus on geometry.  And I would argue that this is the influence of the environment on people’s perception of  what is aesthetically pleasing.  Plants can only mass together when there is plenty of water to share, and if there is not a lot of it, they prefer to give themselves space.

Can a Green Wall Be a Problem Solver?

A green wall, or a vertical surface that is covered in plants, has one great advantage over other types of plantings in small gardens or patios:  it saves space.

One of the principles for designing small outdoor spaces, as many stagers know, is that the smaller the space, the greater the proportion of hardscape one has secure to make the space functional.  For plant lovers, this need for restraint  can be especially painful. Every trip past the local nursery or Trader Joe’s becomes an exercise in denial.

But there is a solution–a green wall.  By sending the plants up the wall rather than across the floor saves the space, and contrary to the usual rule-of-thumb, the more crammed with plants the green wall is, the better it looks.

In San Diego, green walls have a number of other functions worth mentioning:

  •  a green wall, which trickles water through a permeable membrane and planting matrix, cools the air through evaporation when it is very hot and dry
  • a green wall can be planted on two sides, acting as a screen, and doubling its effect
  • a green wall can be used to purify the air.  Many plants soak up volatile organic compounds that are toxic to people
  • plant lovers can have an outlet for their passion in a small space.

One thing to keep in mind is that green walls are not inexpensive.  However, if one is looking for bling in a fourteenth floor condo, renting one for a month is not a bad option.

Raising the Bar: What You Should Expect from a Landscaper

My experience working for Blue Rose Gardening for the last eight years has taught me that what most homeowners want from a landscaper is someone who is competent to make the house look good:  weed, mow, prune, fertilize, replace the occasional sprinkler:  essentially be someone who will do the work  specified and follow directions.

This limited expectation homeowners have is based on a static view of landscaping as an industry and the landscaper as a kind of minimally-trained laborer.  It also implies a static view of the landscape, almost as if it were a kitchen sink, something that needs the occasional fixing in a mechanical sort of way.

You,  your landscape, and your landscaper are all capable of evolving, and ideally, your landscaper should act as a guide in the process.  Here are some areas where you can raise your expectations:

Irrigation

In the Southwest, and San Diego in particular, water is getting more scarce and expensive, and companies who manufacture irrigation products are constantly innovating to improve how water is distributed over the yard.  To give just one example, Valvette Systems, has developed sprinkler stems that have a nut in them, allowing a much greater control over the radius of a sprinkler than can be achieved with just a nozzle.

Little Valve Stems control water radius better than spray nozzles

It is a relatively simple and cheap procedure to change these stems out from an existing system, and having done so will cut down on the water applied to keep the plants happy.  Educated landscapers will know about  advances in irrigation technology, such as this one, and be able to recommend alterations.  Try asking.

Fertilizing and Managing Pests

The view of how one maintains plants in the landscape has shifted in the last ten years from a chemical perspective to a biological one.  Cutting edge farming and landscaping takes this new perspective into account and avoids using chemicals to control pests and improve fertility in favor of biological mechanisms. What do I mean by this?  It turns out that plants, rather than being passively attached to the soil, are actively creating conditions around themselves, especially around their roots.  In fact, these conditions  are so different from the conditions in the rest of the soil that biologists have given it a name–they call it the rhizosphere.  So for instance, it has been observed that certain plants can emit chemicals that attract predator nematodes (a kind of microscopic worm) when their roots are being attacked.   You can learn about the soil food web on your own, but you can also learn from a competent landscaper how to apply principles gleaned from this branch of knowledge to the specific conditions in your landscape to make it healthier–that is, less risk to you and your pets to chemicals–and more sustainable.

New Plant Introductions

“Walking on Sunshine” is a new floribunda hybrid, outstanding for its disease resistance and flowers.

Growers are constantly introducing new hybrids and ornamental plants into the landscape.  Some of these have advantages beyond aesthetics.  Many of the new rose hybrids, for instance, have much greater disease resistance than older plants, and thus require less inputs from you to keep them looking good.

As your landscape evolves over time, your landscaper should have recommendations for plants in places where other plants have not done well, or where some plant has gotten too big or is no longer viable.

Plants as Food

The old thinking about food was that once one had achieved a certain level of economic prosperity, food production could be relegated to the farmers and acquired at the grocery store.  Experts in nutrition, however, now tell us  that plants produce complex chemicals, called “phyto-nutrients” that are key to maintaining our youthfulness and health.  Many of these phyto-nutrients rapidly degrade once a plant has been picked.  So while we can get healthy organic food at the farmer’s markets, there is still no substitute for picking arugula from our own gardens and eating it in salads a half hour later.

Landscapers should support your efforts to grow the healthy edibles at the right time of year.

A landscaper should  be able to help you create a garden and manage it over the course of a year.  Here in San Diego, we can grow food every single day of the year.  A three foot by eight foot plot is plenty of space to grow fresh food for two people.

Final Word

As citizens and homeowners, all of us have a duty to manage the land we have available to us responsibly.  Just as many of us put placards in our yards for the candidates we supported in this last election cycle,  how we manage our land is also a political statement.  Of course our lives are busy; our ability to stay on top of technology and science is limited; and we have many obligations.  But give your landscaper the credit for what he or she brings to your yard.  Hopefully it’s more than just a blower and pruning shears.

If You Love Birds, Plant Scrub Oak

I recently met a woman, I’ll call Margaret for the sake of this article, who doesn’t care about gardening: she doesn’t spend time outside, has no interest in growing her own vegetables–not even tomatoes–she could take or leave flowers.  Her primary concerns in relationship to her landscape are that it not be an embarrassment for the neighbors and that she need put as little energy into landscaping as possible.  We all know have Margarets in our lives.  Some of us may even be Margarets.

I met this woman in front of  the narrow dirt slope that was her front yard after a palm tree and a pine had been removed.  Given the limited space, I had trouble imagining what it must have looked like before, much less how a palm and pine could have looked attractive together.  Talk about an odd couple!  After talking for a few more minutes, in which I desperately searched for any sign of interest in the outdoors, she finally said, “The birds will miss it.”

“The birds will miss what?” I asked

“The pine tree.  The birds were in it all day long.  I would like to re-plant something for the birds.”

I noticed, somewhat surprisingly, that there was a bird bath sitting amidst the dirt of the barren slope.  I had overlooked it before.  Her observations about her lost pine tree were probably correct.  Pine trees, it turns out, support a wide variety of native insects, which in turn support birds, which need the protein insects provide.

Bushtits in Scrub Oak

A little exploration into native ecology reveals that there is a hierarchy among plants in terms of how attractive they are to wildlife in general.  The measure for this  is lepidoptera–that is the butterflies and moths–because these insects have been studied more than any other group.  The more species that like a particular genus of plants, the more essential that genus becomes in supporting animals.   In documenting this, an east coast biologist Douglas Tallamy has come up with a list ranking plants by their ability to support the class Lepidoptera, and thus animals in general.  You can view this link at Wildlife Food-bank (this is my name for it, not theirs).  The pine family, it turns out, are  reported to support slightly over two hundred species of moths and butterflies, which is pretty good.

But topping the list–one can think of it as an All-You-Can-Eat Bird Buffet–are the oak trees.  Oak trees, according to Tallamy’s list, support over five hundred–let me repeat–five hundred species of moths and butterflies.  That is more than double what one can expect from a decent pine tree.  And even though this work was carried out by an east coast biologist, I found out upon doing a little research that the oaks, the great big ones and also their scrubby relations, abound throughout the North American continent.  I found studies talking about their importance in Pennsylvania, in Florida, AND in California.

But this woman had no room on her small plot of land for our large native oaks–the Coast Live Oak, the Interior Live Oak, or the  Canyon Live Oak.  These trees can grow to seventy-five feet tall and have trunks ten feet around.  The only home, in fact, where I have seen a mature Live Oak fit in comfortably in a residential landscape is at the Marston House in Balboa Park.

Scrub Jay in Oak

But this woman had another option, often neglected by homeowners.  She could plant scrub oaks.  These little guys top out at ten or fifteen feet.  Although they probably have deserved their name “scrub” for a reason, they needn’t be in the least bit homely.  With intelligent pruning, these trees can be miniature versions of their grander cousins.  In other words, they can be bon-sai’d.  There are a number to choose from all native to San Diego County:  Quercus, berberidifolia, Quercus dumosa, and wislizenii.  I’ve heard of a fourth, too, Quercus acutidens, but I haven’t been able to verify this one.

If this woman were to plant three scrub oaks on the shallow slope in front of her house, she would create an attractive display of leaf, acorn and bark that would be as appealing to the neighbors as it would be to the birds, that, one would expect, would want to hang out there all day long.  Underneath, I imagine on this dream slope, some of the lovely Pt. Reyes manzanita, which stays low to the ground and gets covered with tiny pink flowers in the Spring.  Small bunches of Douglas  Iris or Snowberry could also help to paint the picture.  And a rock!

Mountain Chickadee on Scrub Oak
Mountain Chickadee on Scrub Oak, common in San Diego