Ask Mr. Smarty Plants

Many people try to grow Magnolia grandiflora (Southern magnolia) in central Texas. Most fail completely or end up with short, chlorotic imitations of what this magnificent tree should be.

Take a look at the USDA County Distribution map. You will see that magnolia's native range is mostly east of the Brazos River. Now take a look at the Growing Conditions for this tree from the page in our Plant Database:

"Growing Conditions

Water Use: High 
Light Requirement: Part Shade 
Soil Moisture: Dry 
CaCO3 Tolerance: Low 
Cold Tolerant: yes
Soil Description: Rich, porous, acid soils. Sandy, Sandy Loam, Medium Loam, Clay Loam Clay, Acid-based, Calcareous

Also, from that same page, here are the normal habitats of this tree: "Native Distribution:Coastal Plain from extreme s.e. VA to FL, w. to e. TX."

I'm betting these soil conditions (except the dry part) don't describe what you have on the west side of IH-35 in Round Rock. Your soils are probably thin, rocky and alkaline. A magnolia is not likely to do well in that kind of soil.

This demonstrates again the desirability of using plants native to the area in which you are trying to grow them, which is the goal of the Lady Bird Johnson Wildflower Center. The magnolia has adapted to growing on forest floors, with a rich humus from centuries of fallen leaves beneath them, in part shade and with plenty of moisture.

You are fighting a real uphill battle trying to grow a magnolia where you are. Mr. Smarty Plants best advice is to start over with a tree more suited to your area.