An estimated 1,200 native flowering
plant species grow in the lower Rio Grande Valley, Texas, and of these at least
28 species reach tree size. The Native Plant Project has selected 28 of these
trees to be featured in this publication. Some are beautiful ornamentals, some
prove invaluable for wildlife use, and others make excellent shade trees.
The lower Rio Grande Valley has a relatively small number of tree species. Many
would not be considered trees in areas with abundant rainfall. Thus, all types
of trees can be considered together in one brochure. The non-exclusive types
include ornamentals, shade trees, and a few primarily useful in restoring
converted natural habitats. Most provide cover, shelter, nest sites, and food to
urban birds and wildlife as they do in their natural habitats.
Trees native to the lower Rio Grande Valley have advantages over trees (even of
the same species) brought in from elsewhere. Trees of local origin have the
genetic factors which ensure greater probability for survival since they are
preadapted having evolved to tolerate local climatic extremes, local soils, and
local diseases and pests. Except for the few species which usually grow with
their roots nearly in the water of the Rio Grande or resacas, most local native
trees are xeric-adapted. This means they require little supplemental water,
tolerate droughts well, and conserve much of the extra water which exotic trees
require. Many fit well into xeriscapes. Native trees have evolved with the
temperature and rainfall extremes and remained relatively unharmed during the
Christmas freezes of 1983 and 1989 which devastated the non-native plantings. A
little extra water though may greatly lengthen the flowering period of
xeric-adapted trees and shrubs.
Using native trees helps conserve rarer tree species which are vanishing as
habitat clearing and conversion continues apace. Over 98% of the natural habitat
of the four-county area has been converted or cleared for urban, agricultural,
or industrial use. Establishing rare species in landscapings spreads out the
individuals so one catastrophe cannot take them all at once and also provides a
reserve seed source in the event the last individuals of a species are
natural habitat. As few as a single individual plant of some lower Rio Grande
Valley species survive in natural habitat.
Some of our native trees are readily available from most nurseries in the lower
Rio Grande Valley. Rarer ones can be found only at the few nurseries
specializing in lower Rio Grande Valley natives. (See list inserted in booklet.)
More natives will become more readily available if you demand them. The Native
Plant Project will provide sources on request; availability of native trees
changes as nurseries change their available selections as demand changes.
Founded in 1982, the Native Plant Project's purpose is to protect and conserve
the native plants (including Endangered), habitats, and environment of the lower
Rio Grande Valley and promote the use of local native plants in local
landscapes. One method it uses is disseminating information about native plants
and habitats. Its definition of a native plant is one native to the four-county
lower Rio Grande Valley (Cameron, Hidalgo, Starr, and Willacy Counties).
The Native Plant Project encourages the protection of native plants through
conserving and restoring native habitats in refuges, natural areas in parks,
wildlife management areas, and private sanctuaries. It works to protect both
natural habitat and the human-influenced environment. It encourages the
conservation of native species through inclusion in local landscapings. The
Native Plant Project works cooperatively with the Fish and Wildlife Service,
Texas Natural Heritage Program, Texas Parks and Wildlife Department, and many
private organizations toward protecting Endangered Species, including those
local natives imperiled but yet unlisted.
The Native Plant Project currently holds general meeting eight times per year.
Members are advised of meetings, field trips, and other activities through The
Sabal, which conveys information on the native plants, habitats, and the
environment of the lower Rio Grande Valley. The Native Plant Project
periodically updates and issues lists of endangered species of the lower Rio
Grande Valley and checklists of its woody plants.
The choice of a native tree, like any
other plant, should be dictated by landscaping needs and the desired effect.
Given the limits of purpose and site, finding a native tree which will
handsomely fulfill every requirement is no problem. Once a choice is made there
remains only a few tree location and planting tips to be observed.
First, get your tree from a reputable, reliable nurseryman. DO NOT transplant
from the wild...not only is this rarely successful, it diminishes our threatened
natural plant and animal habitats. A healthy, vigorous looking small tree is
much preferred over a large one, and smaller specimens suffer less transplanting
shock. Smaller trees, their chances of survival and rapid growth are very high,
do not need staking or artificial supports.
Second, all the native trees do well on most Valley soils. The possible
exception is semi-arid species like mesquite, huisache and paloverde which can
not take poor drainage. Also, few of our native trees will grow on a site where
a large portion of the root area is covered by blacktop or paving. Make sure the
tree has plenty of growing space and be sure not to plant trees too close to
houses, power lines or other structures.
Preparing the Site
A hole should be dug sufficiently
deep and wide enough to hold the full root system. In very poor soils it should
be wider and deeper. As the hole is dug, the soil usually from the top 4 to 6
inches, which is richer should be kept separated from the subsoil. Discard the
subsoil and replace with fresh top soil or improve the subsoil by mixing at
least 1:1 subsoil to moist peat moss or excess media from the pot in which the
tree was growing.
Setting the Tree
The depth of the top of the root
system should NOT be lower than the top of the hole, it usually kills the tree
when planted too deep. Remove tree from container, if roots are so numerous they
are encircling the soil ball, cut the root ball to a depth of 2 inches with a
sharp knife vertically on opposite sides of the ball to encourage roots to grow
outward. If planting a tree with burlap covering the root ball, place tree in
hole with root ball level with top of hole, loosen the burlap from the trunk,
fold back uncovering the top of the soil ball. After setting the tree, soil
should be added gradually working the first lot in firmly at the base of the
root ball, then filling the hole with more soil, the tree may be raised and
lowered during the filling process to eliminate air pockets bringing the roots
in close contact with the soil. When filled, tamp the entire area firmly with
Newly planted trees may need some
artificial support to prevent excessive swaying from the strong winds in the
Lower Rio Grande Valley which will disturb and break up the root system. For
trees up to 20 feet, 1 or 2 strong stakes, 6 to 8 feet, should be driven 2 feet
into the ground about 6 inches from the trunk. Wide cloth tape wound around the
tree and then nailed to the stake will support the tree. Commercial tree braces
Nursery grown trees should not need
pruning. However, during planting branches may be broken. These should be cut
off with sharp pruning shears flush with the branch base or to a growing bud.
The soil around the tree must be
watered thoroughly after the tree is set in place. A ring of soil at the
perimeter of the filled hole, 4 inches high, should be made for holding water.
The frequency of watering depends on the type of soil, the size of tree and the
amount of rainfall. The soil ball around a newly planted tree can dry out
rapidly and Valley showers cannot be depended upon to supply sufficient
moisture. During midspring, summer and midfall months water all newly planted
trees for the first 4 to 6 weeks as often as 3 times a week by filling to the
top of the soil watering ring (during the rest of the year, weekly soaking for 4
weeks should be sufficient). Then every two weeks thereafter for the first year,
should provide ample moisture for your tree to survive. Then let nature do the
Selection of a proper planting site
reduces the need for maintenance. Remember to allow for growth; the mature tree
requires more space than the youngster being planted. Do not plant large trees
under utility wires or eaves or close enough to buckle pavement as the tree
grows. The best times to plant in the lower Rio Grande Valley are late autumn
(to allow for root establishment and dormancy before any freeze) and
mid-February after danger of freezing has passed. Planting during the hotter
months here requires much care and maintenance.
Young trees require heavy watering to establish adequate root systems, then
water can be reduced to little more than nature provides (about 25 inches per
year in Cameron County, 20 inches per year in Hidalgo County, and 15 inches per
year in Starr County). Too much overwatering kills xeric-adapted trees which
cannot tolerate standing in water-logged soils for more than a few days at a
time. A little extra water may lengthen flowering periods greatly. Water
primarily at the drip line (under the outer ring of leaves where rainwater
naturally drips off the tree). Watering at the base promotes weak root systems
that allow trees to blow over more easily and rots the base of the trees.
Pruning should be avoided except to remove dead, dying, or diseased branches.
Remember many of our xeric-adapted trees may drop their leaves when they receive
too little water, a drought adaptation. Try watering before removing them.
Removing too many lower branches reduces their value as cover for birds escaping
urban pets, as well as making them unsightly. Excessive pruning and topping
promotes access for disease organism and pest insects.
Mulching reduces weed growth, soil moisture loss, high summer soil temperatures,
and soil compaction. Pull the large grasses before they become well-rooted and
produce seed. Use of weedeaters and lawnmowers can kill young trees by girdling
the trunks, thus preventing passage of water and food. Keep these machines a
safe distance away. Such mechanical damage also in validates the nursery's
Plant Communities of the Lower Rio Grande Valley
Water, soil and temperature are the
predominant determinants of the Valley's vegetational communities or biomes
which are unusually varied and unique. Four major vegetational areas are the
barrier islands, the coastal prairies and marshes, the river flood plains and
the brush-grasslands. These areas are enclosed by the Gulf of Mexico on the
east, the Rio Grande on the south, the Bordas Scarp (limestone or caliche ridge)
on the west and less distinctively, the South Texas plains in the north.
The tree-life in these four areas is particularly characteristic. On the barrier
islands, except for some scrubby mesquites, huisache and retamas, there are few
if any trees. Moving westward through the coastal prairie and marshes, thesesame
species along with ash, hackberry, and willow become more abundant and larger.
Along the river and resaca banks and in the brushlands areas the number and
variety of tree species increases manyfold. Nature has allowed considerable
overlap in these four areas where a particular tree species might be found
While humans have certainly contributed to this overlap, we benefit from it
because it means our native trees can be grown under a wide range of conditions
with only minor modifications of site or care. Where necessary this booklet
includes such modifications in hopes of insuring success and satisfaction when
you plant one of our native trees in your landscape.