Whale's Tongue Agave at the Dallas Arboretum

Well, considering that Texas is as large as most countries, there is a lot of terrain to cover.  Texas includes everything from marsh, to desert, to mountains and forests.  Geology, geography, water and climate all come together to determine what kinds of plants will grow where.  Yes, you might be able to grow something completely alien to your area, but not without altering one or more of these conditions.

Where I live is primarily a prairie system with timbers crossing here and there where the creeks run through.  The native timbers comprise mainly of Juniper, Shumard Red Oak and Redbud where the soils are shallow.  In the bottoms, there are Hackberries, Pecan, Bois d’Arc, Walnut and Cedar Elm.  The open prairies lands have Passumhaw and wild Plum thickets along with our native grasses – Little Bluestem, Big Bluestem, Eastern Gamagrass, Brown-seed Paspulum, and Yellow Indiangrass, Buffalo Grass and Blue Gamma Grass.  Many of these are now listed on the imperiled or critically imperiled Global Conservation list.

The geology in our area is comprised of rocks that were laid down in fossilized sediments from Cretaceous seas which used to cover North Texas about 80 million years ago.  I know – it’s hard to imagine that all of this hot, dry and often cracking land used to be covered by tons of water, but it was.  The shells of microscopic sea creatures were compressed into limestone, which is what gives our soil its alkalinity – pH of about 8.0.  A lot of plants prefer a much sweeter (acidic) soil around a pH of 6.3 to 6.8.  Silt in the seas became clay and shale.  The clay is actually rich in nutrients, but it is locked away from plants.  The clay also expands and contracts depending on the moisture content, which can be hard on roots and housing foundations.  The limestone and shale were eventually “uplifted”, the waters receded and the Trinity River cut though them carrying sand and soils from elsewhere.  Wind and rain, floods and storms, and decaying matter have all had a hand in changing the composition of the soils over time.  The geology of the metroplex encompasses The Taylor Limestone in far eastern Dallas County, Eagle Ford Shale in western Dallas County, and the Woodbine sands in Arlington and Grapevine.

The geography of our area is mainly determined by water – the three branches of the Trinity River and several man-made lakes.  The Trinity River is the longest river which is entirely in Texas from beginning to end.  The three main branches are the East Fork, the Elm Fork, and the West Fork in Grayson, Montague, Archer and Parker counties and they flow all the way to the coast.  The branch nearest me is the Elm Fork Branch which flows southwest from Gainsville parallel with I-35 and meets up with the West Fork somewhere near the old Texas Stadium in Irving.  We also have Lake Grapevine right in our backyard which is a man made lake fed by smaller creeks between the West Fork and the Elm Fork of the Trinity River.  Why does this even matter?  Think humidity.  No, it’s not a dry heat.  Areas near bodies of water also experience warmer micro-climates.  Bodies of water also have something to do with the patterns of the winds and rains which I haven’t quite figured out yet for our area.

That brings us to climate… if you averaged everything out, the DFW area would probably look idyllic.  BUT… the weather is very erratic here.  The first freeze stops plant growth and has been know to come as early as October or as late as February and yet the average is November 17.  There is often also a late SURPRISE! spring freeze.  Although the average last freeze is considered to be March 14, it has been know to come as much as a month later.

Other factors that effect gardening here are urban warming, severe weather such as hail, tornado and sever thunderstorms.  Denton County has a hardiness zone rating of 8a, but urban areas where concrete holds the heat can have later freeze dates than rural areas.  Urban areas also have higher summer temps and night time temps (as much as 10 or 15 degrees), which become important when growing tomatoes because they like to cool off a little at night.

There you have it… that’s why Texas is so difficult to pin down.  And if you have gardened in other parts of the country, that is why you are having to learn from scratch.  Now, I’m off to clean up more storm damage!