Ask Mr. Smarty Plants

We're not sure we have enough information to answer your question. Tecoma stans (yellow trumpetbush) is native to South Texas, and there are several different species and cultivars that have varying degrees of cold tolerance. McGregor is in the Blackland Prairie region of Texas, with deep lush soils. From our Native Plant Database, here are the Growing Conditions for Tecoma stans:

Water Use: Low
Light Requirement: Sun , Part Shade
Soil Moisture: Dry
CaCO3 Tolerance: High
Drought Tolerance: High
Cold Tolerant: yes
Heat Tolerant: yes
Soil Description: Well drained, rocky, limestone, sand, and loam soils
Conditions Comments: North American native varieties of this species can survive winters within their natural range but may die to the ground during especially harsh winters even there. Varieties sold in nurseries may be from tropical stock and not do so well in US cold. Yellow bells is drought tolerant and Southwestern varieties are adapted to monsoon rains with dry spells between. They may flower better if such conditions are emulated in planned landscapes, so allow ground to dry out between waterings. It is tolerant of confinement if containers are at least 12 inches in diameter and thus makes a good potted specimen. 

You can see that your soils are not what this plant is accustomed to, and Texas has certainly had some early freezes and late freezes this year that might be daunting to a more tropical plant, such as is sold in nurseries. Plant retailers find an annual of this plant more marketable as a patio plant for Zone 9. So, if you bought it already flowering, it may have been one of the tropical cultivars that could not take our winter. McGregor is in USDA Hardiness Zone 8a, which would be all right for the perennial versions, although they might die back to the ground in severe weather.

Since we don't have the answers to the questions of origin of the plant or how long it has been in the ground or if it is getting enough sun, etc. we will generalize some things you can do that won't hurt it and hopefully will help it.

Check the drainage. In your soils, particularly if you are watering, there could be water standing on the roots, which this basically desert plant cannot tolerate. Trim off about 1/3 of the upper growth on the plant, which is what we recommend for transplant shock, which might also be the problem. Do not fertilize-any plant under stress does not need fertilizer to encourage new growth, when its main energies are focused on keeping its roots alive. Control the amount of water it gets-if you have a sprinkler system that regularly waters it, try to re-route the water to cut down from the amount that is going into the soils. The leaves that are turning brown will fall off, they are already dead. Best scenario, there is still enough life in the roots that they can start putting up shoots at the base of the plant and regenerate it. Worst scenario, it is a tropical version of the plant never intended to live more than one year in your area, and is already dead. 

Moral: Try to find out more about whatever plant you see before you buy it. Our mission is to encourage the use of plants that are native not only to North America but to the area in which they are being grown. This is a prime example of why that is a good policy.

From our Native Plant Image Gallery: 

Tecoma stans

Tecoma stans

Tecoma stans

Tecoma stans