COMMON NAMES: POST OAK, IRON OAK, CROSS OAK
BOTANICAL NAME: Quercus stellata (KWER-kus sta-LOT-ah)
FAMILY: Fagaceae (Beech Family)
TYPE: Deciduous shade tree
HEIGHT: 30 to 80 feet
SPREAD: 20 to 20 feet
FINAL SPACING: 20 to 40 feet
NATURAL HABITAT AND PREFERRED SITE: Post oak occurs in all areas of Texas except the High Plains and the Trans-Pecos. It grows in sandy loam soils that are neutral to acid but can also grow in acidic and neutral clay soils. It does not grow in the black and white alkaline or calcarious soils.
IDENTIFICATION INFORMATION: It is a rounded tree with stout, interestingly branched limbs with gnarly growth and rounded lobed leaves. Fall color is less than spectacular - yellow to brown.
FLOWERS AND FRUIT: Flowers appear with the leaves in March through May, male and female catkins on the same tree. Fruit ripens in the fall September through October, small acorns mature in the first season.
BARK: Gray brown, fairly thick and heavy textured even when young and developing into a medium to dark color with age.
FOLIAGE: Leaves are simple, alternate and deciduous. Yellow, unspectacular fall color. Leaves are 4 to 7 inches long, 3 to 5 inches wide with rounded lobes. Side lobes of the leaves are almost perpendicular to the midvein creating a cross-like effect.
CULTURE: Slow growing native oak that hates human activities. Very difficult to transplant. Fairly difficult to grow from seed and is hard to work around without damaging. Post oak needs extremely well-drained soil and neutral to acid soil conditioning. It does not like much fertilizer and needs adequate soil moisture. It is fairly drought tolerant but has been damaged in some of the extreme drought years. Compaction, construction, application of herbicides and synthetic fertilizers have killed many thousands of post oaks and other native oaks in Texas.
PROBLEMS: Wet feet, human impact and secondary attack by insect pest and diseases. The cure is leaving the trees in their native state as much as possible and applying the Sick Tree Treatment to those trees in stress.
PROPAGATION: From acorns planted as soon as they fall from the tree or stored cool and moist at 32-36 degrees prior to planting the following spring.
INSIGHT: This is the most common native oak in North Texas. Many thousands of these trees die every year from damage during construction of new developments because contractors scrape away the top soil and the native understory, compact the soil and change the environment of the feeder roots. To keep post oak alive water moderately, do not fertilizer at all or very little, do not thin out, do not change the soil grade and do not remove the native understory growth. Other post oaks are as follows – Quercus margaretta sand post oak, Quercus drummondii drummond post oak, Quercus boyntonii is the boynton post oak which grows near Lufkin and is a spreading dwarf oak.
Related Q&As on this Subject
Q: I have three large old post oaks in an area where heavy-equipment operators had to drive near the trees and even next to the trunks of two of them. The soil is heavy sandy clay that is very dry. What can I do to minimize the effects of soil compaction? S.A., Decatur
A: Follow my Sick Tree Treatment, which I recently revised. Here is the current regiment: Aerate the root zone. This is especially important in compacted areas. Apply 1/2 inch of compost over the root zone. Apply the following amendments per 1,000 square feet: Lava sand at a rate of 80 to 100 pounds Expanded shale at 150 to 200 pounds Horticultural cornmeal at 20 pounds Dry molasses at 20 pounds Texas greensand at 40 to 50 pounds Mulch bare soil with shredded native cedar. In the spring, as the foliage emerges, spray the trees and soil with Garrett Juice to which garlic tea has been added. In the future, prepare an area before heavy equipment arrives. Spread a 1-foot-thick layer of shredded tree trimmings on the ground around trees and shrubs to cushion the area.
Q. I have had any number of post oak trees die since the severe drought of 2011. I have always assumed that this is still a lingering result of that drought. Some friends have suggested that post oak trees, along with live oaks are also susceptible to the disease. Reading on the internet, I've found it to say that post oaks are members of the white oak family and are resistant to that curse. Any thoughts on this subject? B.N., Dallas, TX
A. You are correct. White oaks such as post oaks are not susceptible to oak wilt. The problem was the drought.