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Friday - August 26, 2011

From: Ennis, TX
Region: Southwest
Topic: Invasive Plants, Non-Natives, Planting, Shade Tolerant, Trees
Title: Native plants for shade in Ennis TX
Answered by: Barbara Medford


My house faces south. The southwest side of the front yard has a Pride of Houston, Japanese Barberry, 2 crape myrtles and some dwarf yaupon hollies. The other section, divided by a stairway to the porch, is completely shaded by a huge oak tree, and it needs to be completely replanted. I am trying to find native plants for the southeast side, the shady side, that would compliment the healthy plants southwest side.


We are assuming that the "Pride of Houston" you mention is a named selection of Ilex vomitoria (Yaupon), native to Texas. Please read this article fom the Plant Conservation Alliance's Alien Plant Working Group LEAST WANTED on Berberis thungbergill, Japanese Barberry, which is both invasive and native to Japan. Lagerstroemia indica, Crape Myrtle, is native to Asia.

Apparently, you are going in the right direction, replacing plants on the shady side with plants native to North America and to your area of Texas, which is the goal of the Lady Bird Johnson Wildflower Center.

Most colorfully blooming herbaceous plants and shrubs need a good quantity of sunlight to fuel their blooms. We consider full sun to be 6 or more hours of sun a day, part shade 2 to 6 hours of sun, and shade less than 2 hours of sun a day. You will need to chart the shade areas by the amounts of sunlight each has. There are other factors besides heavy shade that might cause problems in getting plants to thrive, including the fact that oak roots tend to be in the upper 12 inches of the soil, and form a mat that would be discouraging to other plant roots. In addition, there is the question of allelopathy. 

Various studies have demonstrated that oaks can have allelopathic affects on surrounding plants. Allelopathy is the production of plant inhibiting chemicals by one plant to regulate the growth of others in its vicinity. One important group of chemicals produced by oaks is tannins. They are produced in leaves and litter and also directly by root systems in soil. Tannins are inhibitory to many organisms. Salicylic acid and other organic acids are also produced by oaks and are toxic to other plants. Allelopathy is species specific for the oak in question and the species that is inhibited.

In other words, it depends on which plant and which oak, and we don't have lists of plants that will grow under specific species of oak.

In the "Just for Texans" section of our Recommended Species page, look at the Cross Timbers and Prairies list of plants suitable for that area. Check with the color-coded map at the top of that page and see if you agree that Ellis County is in that area. Also, the paragraph at the top of that page has a description of soils and conditions in that area that should help you in selecting plants. Looking at the sidebar on the right hand side of that page, select "shade" (2 hours or less of sun a day) and "part shade" (2 to 6 hours of sun a day) under Light Requirements, and Narrow Your Search, which will yield a list of 193 plants suitable to your area and the sunlight available. You can narrow the search even more by selecting the same Light Requirements and habit (shrubs, trees, vines) under General Appearance. Clicking on "shrub" will give you 22 choices, "herb" (herbaceous blooming plants) 85 possibilities. Following each link to our webpage on that plant will give you information on projected height, whether it is perennial or annual, even color bloom and time.


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