Sabal Palm planted but not taking off

I planted a sabal texana this past April with a 7' trunk and while it had healthy cut back green leaves, it has yet to take off. Most of the foliage went brown except for the center 2 fans. I don't know if I should keep the ground very wet, moist, or just rely on the rain. I live in the western part of Texas where we get an unreliable 22 inches of rain per year. I also have 2 Washingtonia Robustas that I planted at the same time and one has a crown of big fans and the other is like this sabal, green in the middle, but just sits there and won't take off. I figured it might be too hot (I read somewhere where you're supposed to shade the fans from too much sun when you start them out, which I didn't).
Can you overwater? This is dark black ground with no sand or rocks. I also killed back the bermuda grass in about a 5' radius of the palms with roundup to keep the grass from competing.
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I like the way this author describes growth rate - SLOW! http://www.texasgardencenter.com/sabal_texana.htm
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