Realizing that your landscape requires a lot of water when a drought arrives, is similar to seeing that your roof leaks when it rains. Intelligent people not only repair the damage caused by the leak, but fix the roof also. So, what are you planting now?
When I design a planting project I use the plant species that are native to the part of the state that I am in, only making an exception if there is a really good reason. The process I use to select the species for use at a site and to decide where to plant them is:
1. Determine the characteristics of the various planting niches within that site.
2. Create a list of the plant species that could be native to those particular niches in that region of Texas.
3. Aesthetically place the plants appropriate for each niche at the site.
Determining the Niches
The soil type of each niches helps define it. In the western part of our area, the depth of soil to bed rock is an important factor. Depth determines how deep roots can penetrate, how deep soil moisture penetrates, and how quickly all the soil above the rock dries out during dry spells. This can be complicated to interpret on a site because a crack in the bedrock will often have the deep roots of a species that requires depth, but adjacent to the crack there will be limited root depth. Sun and shade amounts are critical definers of habitat including such subtleties such as areas of shade under deciduous trees that are much brighter in the winter. The changing angle of sun through the seasons is important, especially next to structures which can completely shade plants in one season yet allow full sunlight later. In addition to a variable annual rainfall, the shape of the land affects soil moisture with some areas shedding and others receiving runoff. Local deer population density can also mean that certain species will not survive. Niches usually don’t have sharp edges but often gradually change from deeper to thinner soil, shadier to sunnier, etc.
What is built on a site can drastically change these niches. Some of these changes are primarily determined by the architectural designs, but others are impacted more by the landscape design.
Impervious cover will create new wetter niches where water discharges. Engineers often designed solutions to get rid of water as soon as possible, but starting in the 1980 our company has been using swales and water spreading berms to keep the precious water on site and spread it as much as is feasible. Recently these types of structures have been called “rain gardens”. These structures support and require the local species that naturally grow in water gathering areas.
An important alteration of the niches can be an irrigation system. You can decide to use an irrigation system to create a wetter niche, but then you are committed to always adding that extra water, especially in a drought, or losing your plants. An example of this type of irrigation use is almost every residence in Central Texas that decides to use St Augustine turf and create the wetter niche required for it. Instead, I try to use our irrigation systems for two purposes: 1- for the establishment phase of the vegetation, and 2- to bring the “rainfall” back toward average during dry weather or to mimic dry weather during a drought. (I once saw an example of the opposite strategy – a cactus bed in a botanical garden in Costa Rica that had a glass roof over it to create a dry niche.)
In many suburban areas, especially west of Austin, the deer population is so artificially high as a result of removing predators, that well over half of the native species cannot survive. It is important to make a decision early in the design process on whether to fence deer out of at least part of a landscape and reopen the possibility of using many of the most desirable native perennials and woody species.
Ornamental ponds are a delight for sound, sight and wildlife, but my designs for these include the creation of many moist planting niches to allow for some of the wonderful native riparian species. A well designed natural pond/stream is a very efficient water wise way to create these niches rather than with an irrigation system.
The nature of architecture can often imply soil changes. A level floor on a sloped residential site usually requires retaining walls, fill or terraces on the downhill side. But other changes to the soil niche are driven by the landscape design. You can massively amend a alkaline soil to make it acid enough for azaleas and then keep adding acidifiers for the life of the landscape. Or you can take a thin rocky hillside soil and add extra soil and fertilizers to create much richer planting bed. I find that the best alternative to changing the soil niche, even ones traditionally considered poor soils, is to just find some of the really nice species that like to grow wild in those poor soils.
The Plant List
There are approximately 2,000 plant species native to Central Texas and I have probably included 500+ on the various plant lists that I used in different landscape projects. For any given residential project in Travis County I typically start out with 1-200 species which might be good landscape candidates for that site. Plants that are not on each list are the ones that are not suitable for the niches of the site, plants that I am prejudiced against such as poison ivy and grass burrs, or that the client doesn’t favor (some don’t like yuccas, some love them), small early successional annuals such as the many little euphorbias, or plants that I just have no hope of getting. There are however quite a few native species that are now available from regular nurseries than previously. The Spring and Fall sale at the LBJWFC can also be counted on for additional species. I also keep an eye out for construction/destruction sites where there are sometime some great and ethical salvage opportunities. Some plants I like so much that I am just having to grow small numbers for my clients until someone else decides to grow them. Even though the large majority of plants added to a site will be the easier ones from commercial nurseries, it is often the special plants selected just for that site that give a landscape design an extra special interest. These special species can often become a larger part of the look of a site as they flourish and increase on a site over the first 5-10 years
Placing the Plants
Placing the plants well requires having an aesthetic vision for what you see the site could look like after you plant it, as well as years and decades later. There are traditionally many aspects to this visualizing of a site, from some fairly simple concepts such as putting something evergreen in front of an ugly air conditioner, having a succession of blooms throughout the year, etc to more complex design issues such as lines of site, repetitious forms, etc. That of course requires knowing the plants on the list; which ones are evergreen, what is their ultimate height, the time of year when they bloom, their utilization by birds and butterflies, how dense a deer population they can survive. To all these objectives is added the goal of finding just the right species that fill that function, but which would really want to grow in that niche now and many years later without the pampering common to typical plantings. That is, the planting become “sustainable”, almost on its own. One of the important practical advantages of using Central Texas native species is that you can go look at that plant in the wild and see exactly where it is growing without any human help in its neighborhood for thousands of years, without irrigation water, freeze protection, fertilizers, insecticides/fungicides etc. See where they really like to grow, then visualize those places on your sites.