Texas Mountain Laurel
(Sophora secundiflora) is used in most desert landscapes as
a flowering, evergreen shrub. Of the four common names
associated with this plant, Sophora, Texas Mountain Laurel,
Frijolito and Mescal Bean, Sophora is the most widely used.
Native to Texas, New Mexico and northeastern Mexico, Sophora's
are well adapted to high temperatures, well drained alkaline
soils and full sun. They typically grow quite slowly eventually
reaching a mature height of 15 to 20 feet and 8 to 10 feet wide.
Its slow rate of growth to mature height has led some to
categorize it as a large shrub/small tree.
The form is usually low
branching or multiple trunked with a dispersed to fairly dense
canopy of glossy green leaves. In native settings they are found
growing at elevations from 1000' to 5000'. Sophora's can be
naturalized to survive on average annual rainfall alone in some
desert settings. Supplemental summer irrigations are usually
required in central and southern Arizona. The highest rate of
growth is achieved on established Sophora's when they are planted
in full sun and given deep, monthly irrigations during spring
and summer. The leaves are compound (made up of smaller
leaflets) with 7 to 9, round, 1 inch diameter leaflets. With
proper pruning, Sophora's can be trained into the form of a
small, multiple trunked tree. Be aware that excessive pruning
can inhibit flower production, as Sophora’s produce flowers only
on one year old wood. Trunks range in color from dark gray to
black.
Established plants are
hardy to 0 degrees F. In March and April 4" to 8" bright purple,
drooping clusters of wisteria-like flowers are produced. These
flower clusters are very fragrant with a smell resembling grape
soda. Flowers fade fairly quickly and by mid summer give rise to
3" to 4" fuzzy, tan, seed pods. The seeds are large, 3/8" to
1/2" diameter and dark orange in color. Seeds and flowers can be
poisonous to children and pets. The risk is limited as the seed
pod and seed coat are very hard and difficult to crack.
Placement and maintenance of this shrub should take into account
the risk posed by the flowers and seeds.
Sophora's can be used as
individual flowering shrubs, in groupings to exploit the glossy
green foliage, purple flowers and remarkable fragrance or as a
screen or hedge planting. It mixes easily with other desert
landscape plant materials and adds a unique color and texture to
the landscape. It will tolerate planting in or near turf or in
more native areas. Sophora's are thornless.
The only insect pest of
any consequence is the larvae of the Pyralid Moth that feeds on
leaves, young twig growth and immature seed pods. It is readily
controlled by application of Bacillus thuringiensis
(sometimes called BT), a widely available, commercial biological
control agent. Sporadic availability and the relatively slow
growth rate have limited the use and popularity of this shrub.
Proper maintenance can enhance the growth and increase the
popularity of this remarkable yet under-appreciated flowering
desert shrub.