Weekly Express-News Article

By Calvin R. Finch, PhD, SAWS Water Resources Director, and Horticulturist

Saturday, September 13, 2008 

“Blooming Groundcovers”

            As we move into the autumn, consider planting one or more of the blooming groundcovers. 

             The full size Mexican petunias are very difficult to control.  They spread by seed and roots and can move across country at a remarkable speed.  The smaller cousin, dwarf Mexican petunia, is superior in every way to the invasive large version.

             Dwarf Mexican petunia is vigorous enough to fill a bed when the plants are placed on two foot centers, but they will not usually spread beyond the borders of the bed.  The soft leaves (one inch wide) are straps that reach three to four inches long with a pointed end.  The foliage is a handsome dark green that forms a dense groundcover.  

 The foliage and growth habit make dwarf Mexican petunia a good groundcover, but they also have handsome blooms.  The “Katy” selection is a blue/purple color and “Bonita” is pink.  There is also a white bloom.  Dwarf Mexican petunia blooms best in full sun, but the foliage is shade-tolerant.  They make an especially good groundcover under deciduous trees.  In such conditions, they seem to have two bloom periods; in the spring before the leaves develop and in the autumn after the leaves fall.

The blooms vary from nearly flat to tubular.  The face is about quarter-size.  They are utilized by both hummingbirds and butterflies as a nectar source.

During severe winters, the Mexican dwarf petunia may defoliate, but they are consistently root-hardy in South Texas. 

Deer eat dwarf Mexican petunia in a drought, but it is not their favorite food source.

In addition to a groundcover, dwarf Mexican petunia is disciplined enough in growth habit to use as a border (1 – 1.5 feet tall).  They also make a good container plant.

Bearded iris is one of my favorite plants.  There are very few plants that are as drought-tolerant and soil-tolerant as iris and none that have a beautiful orchid like bloom every spring.

Plant iris in full sun.  It is hard to believe that all those iris beds we see were originally in full sun, but it is true.  Many of the beds are more that 100 years old.  They were planted in full sun, but over the years the shade trees grow up over the beds.  Iris in the shade may have a few blooms each year and the foliage sometimes still looks good, but they benefit greatly if they are transplanted to full sun.

The best time to transplant iris is in the fall, but they will survive the change year round.  The rhizomes can even sit in a sack for a year and still grow when finally they are planted.

The key to iris planting is to place them at a depth so that the rhizome top is even with the soil surface.  The leaves can be left in tact or trimmed to half size. Plant the large selections of iris on two or three foot centers.  The small cemetery type iris look best when planted on one foot centers.  Beds bloom best when they are thinned every three years.  Make new beds with the excess rhizomes.

            Iris blooms can be very large, up to six inches, and some varieties have distinctive pleasant fragrances such as lemon or grape.  The fancier bearded iris bloom in March or April.  They can be blue, white, yellow, maroon, brown, and purple.  Almost every color except red. 

            Cemetery iris have smaller blooms and flower early, usually February, but sometimes in January.  Their flowers are white or blue. 

In most situations, iris are not eaten by deer.  The sword-like foliage is evergreen and attractive.  Even when they are not blooming, iris are a good groundcover.

Large bearded iris are sold by nurseries as a dry rhizome or in one gallon containers.  The best way to obtain cemetery iris is to receive a neighbor’s extra rhizomes. 

Society garlic is another deer-proof desirable perennial that makes a good groundcover.  Like dwarf ruellia it will grow in sun or shade, but blooms best in full sun.  The foliage looks like onion tops (and smells like it too!).  The tubular lavender blooms are borne on stalks that may reach two feet tall.  Society garlic is sold in four inch and one gallon containers.  Plant them on one foot centers for solid coverage or on two foot centers for a specimen plant.  Society garlic looks good as a border and does well in a large container.