Texas Mountain Laurel (sophora secundiflora) is indigenous to the Texas Hill Country and the Trans-Pecos region. This beautiful evergreen flowering shrub is seemingly surrounded by a veil of intrigue and mystery. Not well known or planted much outside its home range, Texas mountain laurel could be utilized as an outstanding landscape specimen over much of the state if it were better understood.
The controversy begins with attempting to define this plant as a tree or a shrub. The simple definition has always been that a tree is something we can walk under and a shrub is something we must walk around. Holding to this definition I would have to say that Texas mountain laurel is mostly a shrub. Most authors seem to agree.
Benny Simpson, the recognized expert on woody species in Texas, does not list Texas mountain laurel in his book Texas Trees but does list Eve’s necklace (sophora affinis) a close relative as being a tree. In the “Texas Native Plants Database” (http://horticulture.tamu.edu:) Mr. Simpson defines the mountain laurel as a shrub but gives average height as being 15 to 35 feet (definitely tree size) with an average width of 10 feet. Sally and Andy Wasowski in their book Native Texas Plants list the Texas mountain laurel as an ornamental tree and estimate height as anywhere from 6 to 30 feet. Go figure.
Actually what this should mean to the home gardener is that mountain laurel is a large shrub or small tree (if you prefer) that may reach 30 feet or more given enough time and the right conditions. Further study will reveal that most of us shouldn’t worry about that maximum height because this is not a fast growing plant and by nature a 30 foot specimen would also have to be VERY old. So God grant you should live long enough to have that problem. At any rate the slow growth factor will make this shrub easy to control if necessary.
In the home landscape I like to use Texas mountain laurel as a focal point. It works well anywhere you might use standard yaupon, crepe myrtle, or any of the mid-sized junipers. The shiny dense evergreen leaves look good in all seasons and the showy fragrant (reminds most people of grape soda) blossoms are a real show stopper in early spring. I especially like to plant it where the prevailing wind can drift that scent toward the house or sitting areas. In my opinion Texas mountain laurel would not be a good choice for screening because of the slow growth rate Unless you are very patient or you are lucky enough to find and be able to afford large specimens to begin with.
Another intriguing issue concerning our mountain laurel is cold hardiness. Before people like Benny Simpson began researching our native plants, there was little information as to just how far outside their native habitat these plants could be grown. Referring to the Texas Native Plants Database again, Mr. Simpson gives the cold hardiness zone as USDA zone 8. He makes the observation that in climates colder than zone 8, “flowering is not reliable because of late freezes.” He does not say that the plant will not survive in zone 7 or above he simply states it may not flower well. However, in doing my own research I turned to the Atlas of the Vascular Plants of Texas and found that some of the counties (particularly in the Trans-Pecos) in which sophora secundiflora has been reported are apparently in zone7.
To further confuse this issue, we recently received a new hardiness zone map just published by the American Horticulture Society which now pushes the northern border of zone 8 to the Red River in North Central Texas. Whether this is due to recent warming trends or a response to better weather data, it does seem to show some justification for those of us in North Texas to continue to experiment with zone 8 plants.
Some years ago I had the pleasure of being introduced to Steve and Sherry Bieberich, owners of Sunshine Nursery in Clinton, Oklahoma. Clinton is smack dab in zone 6 where winter lows typically dip below the zero mark. Yet there is a Texas mountain laurel growing in the demonstration gardens that judging from its size had been there for awhile. According to Steve, this specimen had been grown from seed collected from high elevations of the Guadalupe mountain range. Naturally I was compelled to purchase a few offspring from his plant to experiment with at our nursery in Wichita Falls.
Several years later a fine old specimen was found here in Wichita Falls by Phil Hague, one of our former employees. That spring the plant was putting off a profuse bloom which resulted in many seeds that were collected by Phil. Judging from the age of the vacant house at which it was found, the shrub had to be at least 40 and may have been as much as 80 years old. Unfortunately, this venerable shrub was destroyed the very next year when a new business bought the property, but thanks to Phil the seedlings live on. This and other sightings of Texas mountain laurel made it obvious that it had been used as a landscape plant here in North Texas in years gone by.
My conclusion from all this is that Texas mountain laurel apparently is cold hardy at least to southern areas of zone 6 and that further experimentation and selection of hardier genotypes may push it even further north. In the past 12 years I have not seen our mountain laurels damaged by winter cold at all. But I do agree with Mr. Simpson that the flowers may be lost to late freezes in some years.
One last bit of intrigue that may help explain the general lack of popularity is that the plant is quite poisonous. The flowers smell good and the bright red seeds do resemble some types of candy. However, the seed are extremely hard to extract from the pod usually requiring a hammer or some other tool to get them open. History tells us that several Southwestern Indian tribes did use the beans (also known as mescal bean) as a potion in certain rituals. Used in the right amount this drug could induce powerful visions. Ingesting too much could certainly kill a person. You may also find it interesting to note that one of the common Anglo names for the plant was “big drunk bean.” So perhaps a few of the European settlers may have had a taste as well. While this may cause concern among some folks the facts are that plant poisonings reported in the United States are very rare. Besides if you do a little research you will find that you probably already have some poisonous plants in your landscape. Don’t deny yourself the beauty or the ease of growing Texas mountain laurel. Just don’t eat it. OK?
Other criteria for growing mountain laurel concerns soil and soil moisture. The plant thrives in the highly alkaline limestone soils of the Edwards Plateau. It will not tolerate soils with an acid ph. Positive drainage is also critical. This is one of the most drought tolerant shrubs in the landscape industry. Once established the plant will survive on rainfall alone. In heavy clay soils it should be planted high and dry. The ideal raised bed for mountain laurel should contain a good portion of compost mixed with plenty of limestone gravel. As you may have already guessed, hot weather is not a problem.
Although Texas mountain laurel does spill across the border into Mexico and New Mexico, Texas is its true home. Indeed, it is found no other place in the world. In my opinion, sophora secundiflora (a close cousin to our bluebonnet) should be nominated as our state shrub. Currently the crepe myrtle (from Asia) holds that honor and distinction. While I do love the crepe myrtle for all its beauty it seems to me that the plants we choose for the official state emblems should by their very nature be true Texas natives. Texas mountain laurel accurately reflects the spirit and tenacity of Texans as it remains green in the cold of winter, flourishes in the heat of summer, and brings forth astonishing beauty each spring. Now…….do I hear a second to the nomination?