I added some Hens and Chicks to my succulent garden today. Pulling back an inch of gravel mulch, I nestled their roots into the soil underneath and then immediately watered them in. The whole time I worked though, my mind kept heading back to the desert, seeing the tiny Clustered Pincushion and the massive Saguaro cacti rising out of the bone dry landscape of sand and rock. On one hand, it is almost inconceivable to me that any plant life can exist at all in that harsh environment, but on the other hand, the old adage of Right Plant in the Right Place rings true.
So often, when we’re looking to fill a spot or we run across a new, unfamiliar plant, our first questions tend to be “sun or shade; dry or wet?” Granted, they are important questions, but they don’t really give the whole picture; the details are missing. Many other environmental factors also affect a plant’s ability to thrive. Soil type, timing of rainfall, exposure to wind, humidity levels, winter temperature ranges, winter sunshine, amount of snow and ice, day length and heat tolerance all play into a plant’s success or failure.
With that in mind, Right Plant in the Right Place takes on a new dimension. Before you can match a plant to a place, you have to thoroughly understand both the general environment of the area as well as the unique subtleties of the place in which the plant will live. Knowing that the soil is clay, that summers are hot and humid, that August is a dry month and that it snows in the winter isn’t quite enough.
Soil types can vary within a few feet. Unexpected pockets of rock or clay can impede root development, resulting in weak plants unable to absorb enough nutrients to fight off insects or diseases. Poor drainage means water-logged plants in rainy spells and parched ones in dry times. A highly acidic or alkaline soil can be slowly toxic to some varieties. Knowing about the soil in the spot you are planting is crucial.
Every yard has microclimates within it where conditions are slightly different than the rest of the space. Hedges and fences can block drying summer and winter winds that otherwise sweep through the landscape, quickly dehydrating plants. Walls, driveways and sidewalks can create heat islands, reflecting and magnifying the intensity of the sun’s rays. Low spots can allow cool air to pool, slightly reducing temperatures in both summer and winter. Having an understanding of the specific climate pockets increase chances for success.
Since its initial publication in 1960, consumers have consulted the USDA’s Plant Hardiness Zone Map to determine if a plant is likely to withstand cold winter temperatures. The hardiness maps, using data from ten-year periods, divide the country into geographic regions, with Zone 1 having the coldest average temperatures and Zones 12 and 13 having the warmest average temperatures. Each region covers a 10 degree range, with zones 2 through 10 subdivided into parts “a” and “b”. Growers then routinely label the zone ranges for their plants so that consumers can determine if the plant is appropriate for their area. An interactive USDA Plant Hardiness Map is available on line at https://planthardiness.ars.usda.gov/PHZMWeb/InteractiveMap.aspx
While cold hardiness is an issue, a plant’s ability to withstand extreme heat is also crucial. Heat stress can slowly take its toll on plants, drying up flower buds, sapping foliage of moisture and color and leaving roots stunted. In the late 1990’s, the American Horticultural Society developed the Heat Zone Map, which is based on the average number of heat days, days in which the temperature climbs over 86 degrees F., an area can expect. Zones range from 1, which experiences no heat days to 12, which expects at least 210 heat days per year. (If you’re curious as to why 86 degrees F was chosen, it is the temperature at which plants begin to show signs of physiological change.) Some catalogues utilize the Heat Zone Map, but it has not found its way into common usage. The map can be found online at http://solanomg.ucanr.edu/files/245158.pdf
When we are getting to know someone, a common question is “Where are you from?” Connecting an individual to a place can give us a sense of the person’s background and identity -- what he or she is familiar and comfortable with. As crazy as it sounds, asking the same question to new plants we meet can help us get to know them as well. What is the plant’s native habitat? How closely does its native environment mirror our planting area? Will accommodations for soil or light, moisture or humidity be needed? Are the adaptations sustainable all year, or will we need to make seasonal changes? Are the adaptations really worth the time, effort and expense or is there a better choice closer to home? Would a native plant, already attuned to the environment, be more likely to thrive with minimal effort on our part?
Coming full circle to the desert, the vegetation that I saw worked there because it belonged there. Over eons of time, it evolved with and adapted to its surroundings, creating an extraordinarily beautiful natural landscape. Truly the Right Plant in the Right Place.
Join us next time as we look at water-wise landscaping, another lesson the desert has to offer us.