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Friday - January 09, 2015

From: Austin, TX
Region: Southwest
Topic: Xeriscapes, Compost and Mulch, Planting, Soils, Drought Tolerant, Herbs/Forbs, Shrubs
Title: Converting a Texas backyard to grow Xerophytic native plants
Answered by: Guy Thompson

QUESTION:

I am planning the conversion of our backyard, about 4000 sq ft of largely St Augustine, into a grassless landscape of hardscaping and native plants. I�ve been an avid gardener of rock garden plants in the east and in my new garden I want to grow small Xerophytic perennials and dwarf shrubs that can adapt to this dry and droughty environment of Austin. The soil structure I have to work with is one of about 18� clay over a hardpan. It�s pretty clear that drainage is going to be an issue in growing the plants I want. It occurred to me that a solution might be to build berms (sloping mounds or ridges without walls) to get the drainage I need. Raised beds are another possibility but berms appeal to me because they let water drain laterally and offer more planting area and microenvironments than a flat surface. Building a berm of perhaps 20 feet by 10 feet with heights up to about three feet could be an expensive proposition, though. I�m reluctant to use construction fill to build up the base and save cost however because many rock garden plants have long taproots. It occurred to me that I am going to have a lot of St. Augustine sod to remove. I could pile the sod up to build the base of a berm and then cover it with 12 inches or so of the gritty soil mix that the plants need followed by a pea gravel mulch. Variable size rocks and a boulder or two will be set into the berm to stop erosion and provide planting niches. What do you think about the idea of using the reclaimed sod to build up the berms? Have any gardeners in Austin tried using berms to grow rock garden plants? Are there any garden designers or landscapers who have tried this? Thanks in advance David Guillet

ANSWER:

You have a very ambitious plan, David. It sounds like a lot of fun. For the most expert advice, you might want to talk with Jill Nokes, an excellent native landscaper here in Austin. She generally works with larger habitats these days, but she can offer you good advice and names of other highly qualified landscapers.

I like your idea of berms and using unwanted sod to bulk them up. One problem is the possible emergence of buried grass later in the year. St. Augustine should not pose a question, but most Austin lawns also contain bits of Bermuda. This grass would give you many headaches if it should reappear in your berms. It would be best to kill the grass before removing the sod. Solarization is the most conservative method, but it would take forever in the winter. When I converted my lawn to Habiturf I sprayed the St. Augustine/Bermuda with Roundup and sprayed any green areas again after ten days. Roundup is a non-persistent herbicide that works best when grass is growing but should do the job in cold weather too.

After the grass is dead, scalping the lawn with your mower will remove much of the thatch before you use a sod cutter. Soil amendments should include lots of sand to improve the permeability of your clay soil and more organic matter and/or high quality topsoil. There is probably no need to worry about the pH of the soil if you are planting Texas natives, which are already adapted. Rototilling the mix will break up some of the sod pieces. Watering the berm should facilitate settling to a final desired level.