Ask Mr. Smarty Plants

Hesperotropsis leylandii (Leyland cypress), which has many synonyms (e.g., × Cuprocyparis leylandii, x Cupressocyparis leylandii, Callitropsis ×leylandii, × Neocupropsis leylandii) is a hybrid (Hesperocyparis macrocarpa – Monterey cypress × Callitropsis nootkatensis – Alaska cedar).   It is not a 'natural' hybrid because the native range of these plants is separated by some 400 or so miles.   It was hybridized in Wales where the two species (Monterey cypress and Alaska cedar) were transplanted and grew in close proximity.  So, even though the parent trees are North American natives, it isn't considered a native of North America.  True, it does grow fast and would form a thick hedge, but it has shallow roots which, with the fact that the range of its parent trees is the northern part of the west coast of North America, do not make it a good match for the hot Central Texas summers.  

Green Giant Arborvitae, Thuja (standishii x plicata), is also a hybrid—a cross between Thuja standishii (Japanese arborvitae), a native of Japan and Thuja plicata (Western red cedar), a native of the North American west coast from northern California to Alaska.  It is a fast grower, too, but again the native range of its two parent components would not recommend it for hot Texas summers.

There are two native evergreens, however, that are well-suited to the climate and soils of Central Texas:

• Juniperus virginiana (Eastern red cedar)  There are several varieties that will readily form hedges and it is very tolerant of pruning.  Here is some information from Neil Sperry about planting them.  This species is more likely to be found in local nurseries than the following species.
• Juniperus ashei (Ashe juniper)  Ashe juniper would also make a great hedge, but probably not as popular a choice as Eastern red cedar because of its reputation for producing allergies from its pollen.   In fact, both juniper species produce pollen that is an allergen to some people. Only the male trees, NOT the female trees, produce pollen but unless the trees are mature it won't be easy to tell the males from the females.

There are several other evergreen shrubs or small trees that can be used as hedges in the Central Texas area.   They won't be as dense as the two junipers but could be mixed together or with the junipers for an effective barrier.  Please read the species' page for information about its size and growing conditions.

Morella cerifera (Wax myrtle)

Rhus virens (Evergreen sumac)

Leucophyllum frutescens (Cenizo)

Sophora secundiflora (Texas mountain laurel)

Ilex vomitoria (Yaupon)

Prunus caroliniana (Cherry laurel)

Here is more about evergreen hedges for Texas from Neil Sperry's Gardens