Berms in Central Texas

Submitted by David Guillet on Wed, 01/07/2015 - 11:10
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” of clay over a limestone hard pan (caliche). 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. I am going to have a lot of St. Augustine sod to remove. Would it feasible to 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 would 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 the region tried using berms to grow rock garden plants? Are there any garden designers or landscapers who have tried this? Thanks in advance David Guillet


Submitted by Fermi on Wed, 01/07/2015 - 17:46

Hi David,

I can't say that I gardened in Austin but I did live for 18 months "next door" in Northern Louisiana and visited cousins in Austin a few times - they had Zephyranthes drummondii naturalized in their lawn!

Where I live currently in Central Victoria is somewhat similar in climate and we do use berms! We call them mounds and they are edged in rock but essentially they give the plants a great root zone to grow in as the natural soil is heavy adobe-type clay which is glug in winter and concrete in summer. Our mounds were created by getting an excavator to pile up soil mixed with organic matter and grit/coarse sand/gravel into flattish mounds sitting 18 to 20 inches above the surrounding soil height.

I don't believe in importing soil into the garden as this usually introduces weeds. Composted garden waste and prunings is what we usually get and mix in whatever grit we can get and top off with a mulch - gravel for rock plants and organic matter for others.

We mostly constructed the mounds to plant small trees such as Chinese Pistachio,  Crataegus and Sorbus but these are under-planted with hundreds of bulbs such as iris, liliums, narcissus, tulips, triteleia, habranthus and  zephyranthes. Where we supply some summer water we also grow rock plants such as Penstemon, Oenothera ands aster.

I hope this is helpful for you



Submitted by penstemon on Thu, 01/08/2015 - 12:45

In reply to by Fermi

One of the few guarantees in life is that berms made of soil will sink, sooner rather than later. 

Three pictures attached. Berms are necessary here because the soil is subsoil trucked in from somewhere else when the neighborhood was built. (The native soil is decomposed sandstone, very nice.) Digging in the soil is like trying to get a spoon into frozen ice cream; same texture.

First one is "Mount Zot", which was made from turf, inverted and piled up. The level has sunk about two feet in twenty years. (Hard to see in the picture, maybe.)

Second is a newer berm, about three feet (1m) higher than the path leading to the arbor in back. This has a "backbone" of broken concrete, old tires, old National Geographic magazines, and maybe the old "exer-cycle" (can't find it, so maybe it was buried). The growing medium is pea gravel and sand, with no organic matter. No irrigation is needed because all rainfall goes directly to the roots. (Just the opposite of what "drainage" suggests.)

Third is another raised bed, "backbone" of cinder blocks. This was made out of soil, which sank, and now the composition is about ten percent soil and ninety percent gravel. The bed behind it, on the other side of the weirdly-branched Crataegus ambigua, is pure gravel and sand. 

(Ignore the snow; it's about 50F, 11C in the shade here.)

Using soil to build up a berm is not entirely problem free as Bob's photos suggest.  I might want to rethink using construction fill instead.  Here in Austin there is so much construction of buildings and roads that getting rid of the excavated limestone is a problem. Its quite inexpensive and often free at many sites. Someone else in a local gardener blog also pointed out that Bermuda grass is pervasive here and can be a real problem if it is not entirely removed. Usually that's done through solarization in the summer (quickly in 100 degree weather) or Round Up in the winter

Newspaper several sheets thick will take care of the grass. You can make a berm on top of that. I'm jealous of the limestone; all we have here is granite, which is okay, but it isn't limestone. 

It helps to know the habitat of the plants you intend to grow, and especially, the soil texture and rainfall patterns. Soil texture is a critical factor in survival of xerophytic plants during drought. A lot of that information is available on the Lady Bird Johnson site, 

Our new home that I'm landscaping is about 15 minutes down the road from the Lady Bird Native Plant Center. I started to volunteer there when I arrived a couple of years ago.  That's when it dawned on me that I could grow natives and adapted plants if I studied the environmental setting of central Texas and rethought my approach.  I gardened at my summer place in the Shenandoah valley with deep sandy loam and a completely different climate. None of the plants I grew and few of the techniques I used would work here.

Lady Bird is indeed a fantastic resource.  A few years back it was turned over the University of Texas to run. That's stabilized it financially although they have had to cut back in some areas.  What I think mattered were connections that developed between some of the academic departments, such as Landscape Architecture and the Botany program in Biology. The center has a very accomplished staff.

What I don't feel here is a coherent sense of "rock gardening" as we understand it.  Don't bet me wrong...everybody has rocks in their gardens given the geology of Central Texas and there are some excellent plant nurseries that due to the Lady Bird center's influence sell a huge number of natives (also because of water scarcity). And there is a very active cactus and succulent society here. But I miss a shared understanding of the content our community attaches to "rock gardening" e.g. its history, origins in England, key figures, our approach to what is a "rock garden" plant,  ... 

Maybe it will happen over time. It was encouraging to see the formation of a New Mexico chapter of NARGS and I look forward to visiting the nurseries and botanic gardens there and in Colorado.

Yes, the wildflower site is excellent, especially since they are open to being corrected on their botanical nomenclature. (I got them to change the name of Vernonia lindheimeri var. leucophylla to the accepted name, V. larseniae.) 

One problem you might face in visits to states to the west of you is that the rainfall there mostly comes from thunderstorms, which makes a huge difference in the way plants respond to water, and in the soil textures in which they can grow. A plant that grows in gravel in New Mexico does so because it can make the most efficient use of the rain that falls on it; in a climate with regular rainfall like Austin (according to Wikipedia) this might require a different technique. 


I second that. 

One of the important things in rock gardening is being able to filter regionally-oriented cultivation information from general information useful in all climates. It isn;t always easy to do that, and local gardeners can be a big help. 

Submitted by David Guillet on Sat, 01/10/2015 - 17:00

In reply to by penstemon

I feel like a relative newcomer still trying to get a sense of the gardening community. Just today I was leafing through a couple of respected books by Sally Wasowski and others, Landscaping with Native Texas Plants (1985)  and Native Texas Plants: Landscaping Region by Region (1997). Each one has a page or two describing what a Rock Garden is from our perspective (English origins, small alpine plants, natural looking rockery ...) and mentioning the constraints in making this model fit Texas soils and climate. Each description is followed by a sample rock garden plan .  So these authors at least are certainly aware of the rock garden tradition.

I'll keep my eyes and ears open to see what the possibilities might be. 

One criticism I have of the chapter on rock gardens is all the talk about "drainage". Plants don't need "drainage". The author does then contradict the idea of "drainage" with the correct statement that rocks help channel water to the roots. That's what happens in real life. Chasmophytes, for instance, grow in rock crevices because they can, not because of any need to "drain away excess water". 

Another thing I might mention is that some of the recommended plants come from quite disparate climates. Look at the Wikipedia entry on the precipitation of Alpine, for instance, compared to that of the Hill Country. 

Now that the snow has evaporated from the new sand pile, here it is in all its glory. The cages are, of course, an artistic statement, rather like gardens filled with sculpture. (They also serve as protection against rabbits.)

The sand pile is half sand (hence the name) and half pea gravel. About two feet (60cm) high, up at the top center of the picture. I stuck in a couple of rocks for looks. 

Submitted by David Guillet on Wed, 10/21/2015 - 13:59

Here's an update on my rock gardening project in Central Texas.  Berms were built on a base of broken up cinder blocks. Several inches of Thunder Dirt were then added followed by a mulch of decomposed granite.  Thunder Dirt is formulated for native plants from non-shrinking compost and decomposed granite and is a popular soil mix for plantings at Lady Bird Wildflower Center.  The berms were part of a project which included mixed borders. Drip irrigation was installed in the borders and it wasn’t that expensive to run drip through the berms.  Once plants are established I don’t plan to irrigate the berms regularly.  The drip will be kept for insurance if there is a serious drought.

            I planted about half the surface area with mostly native plants no more than 12” in height.  The majority came from a plant sale at Lady Bird.  I’ll finish planting out the berms in the spring focusing on small succulents and cacti and plants from the seed list and nurseries I can try from similar climates elsewhere.Here is a list of what went in after the construction:

Acalpha radians

Agave havardiana

Asclepias oenotheroides

Berlandiera lyrata

Callirhoe involucrata

Callirhoe involucrata var lineariloba

Calylophus berlandieri

Chrysactinia Mexicana

Dalea greggii

Dalea purpurea

Dichondra argéntea

Euphorbia antisyphilitica

Glandularia bipinnatifida var bipinnatifida

Heterotheca canescens

Liatris punctata var mucronata

Machaeranthera tanacetifolia

Manfreda maculosa

Manfreda sileri

Marshalia caespitosa

Melampodium leucanthum

Paronychia virginica

Penstemon baccharifolius

Penstemon wrightii

Salvia engelmannii

Scutellaria wrightii

Stemodia lanata

Teucrium cubense

I’m going to watch closely to see how the berms hold out.  As I write, 4” – 6” of rain are predicted over the next four days and the El Niño predictions for the fall and winter are off the charts. I hope the berms are still there by the spring

            I was able to find some nice honeycomb limestone for the berms.  This rock is endemic to Texas and has a honeycomb of chambers caused when seeping rainwater mixes with sulfurous gases in cracks and dissolves the limestone.  The large ones came from a supplier and I found the smaller ones free on Craig’s List. Limestone is usually available for free most days on Craig’s list and honeycomb comes up if you look carefully at the photos and get there quick. I also found a couple of pallets of flat honeycomb to use to edge the mixed borders.




Submitted by DesertZone on Thu, 10/22/2015 - 19:05

I really like what you have done and love your plant choices.  I bet that was a lot of fun creating such a cool space.  

Submitted by David Guillet on Fri, 10/23/2015 - 06:39

It was indeed an incredible amount of fun planning the garden. I really appreciated the comments from you folks on the project.  Finding a good contractor who was willing to try something new helped a lot. 

Now I'm thinking about possibilities from the seed list.  I tried starting seed from the list last year using techniques I had success with in the East. Dismal failure.  So I've shifted my volunteering at Lady Bird to the propagation section. Advice and experience there should help.  (Maybe I can sneak a flat or two into their greenhouse!)


we'll be looking forward to seeing how your berms develop. I remember visiting a native plant center in either Austin or Houston back in 1996 and was impressed with how much color you can get with just using local plants. I especially loved the blue lupins and the orange asclepias which flowered along the highway,



Submitted by IMYoung on Fri, 10/30/2015 - 13:35

In reply to by Fermi

For sure you will get a lot of satisfaction from growing plants in your super project.  Enjoy!


Submitted by David Guillet on Sat, 10/31/2015 - 08:33

Well the forecasts were right.  We got 7” of rain in the early morning of Saturday of last week and an incredible 13” over about 8 hours yesterday.  The berms held up and not a piece of granite mulch was out of place.  No plant seems to be for the worse and most appear to be thriving. These plants need lots of moisture to get established, and they’re getting it to say the least.

What I did notice was a result of the layout of the berms.  There were two, set to face north curving on each end to afford east and west exposure.  Surface water flows south to north and the north facing berms acted a dams forcing runoff to the ends of each berm. The berms themselves were unaffected but it left a mess at a couple of places in the mixed border with a loss of soil and mulch.

I can fix this by digging a couple of shallow trenches edging them with limestone and filling them with river rock. But it impressed on me the impact that berm layout can have on surface water drainage.

So far, so good ….

That was a LOT of rain. Why is there never a happy medium with the weather?!!


I know  that  the effects on surface drainage and storm run-off are often a nasty surprise to householders in the UK who  cover their gardens and driveways with the brickwork we call "lock-block"   or tarmac!

Submitted by David Guillet on Wed, 03/16/2016 - 15:50

This is a copy of a reply to Fermi about how the garden was going 

Things seem to be going well. Most everything that went in the fall has survived this winter so far. It has been a very weak winter to say the least. I could probably count days when the low went below freezing on one hand.  At the moment its 91, 20 degrees above normal and a new record.  Well I guess records are meant to be broken. but I haven't found a plant yet that's noticed. 

Oh, yes we got 3" of rain last weekend. Here's a photo of the berms as of today March 15

Melampodium leucanthum and Tetraneuris scaposa have been blooming since December. 


I have a couple of batches of natives and exotics coming in April from specialist nurseries in Colorado. Its rather late

to put in transplants in in Central Texas given how early the heat arrives.  Will be a good test. Fall is a much better time

Here's a shot of the mixed border

Again nothing untoward. This part of the garden got 4 to 6" of Thunderdirt over clay, topped off with a pecan shell mulch. I've been putting stuff in all "winter" a few from local nurseries and a few from shippers in California. 

The real test will come when we start getting those 100 degree days!



Hi David.

it will be interesting to see how things survive the summer. What we found when we moved to this area which has a much hotter and drier climate than Melbourne was that things we took for granted back there simply dwindled away or died outright due to the change of environment. One of our biggest problems was a lack of shade and it took a long time to grow the trees which now provide some respite from the sun, but there were many things which surprised us by thriving.

Fortunately many Australian native plants are suited to our conditions. You may say "Of course they would - they're Australian!" but some of them come from the other side of the country (Western Australia) but enjoy a similar climate "at home".

Sticking to your local flora would be a safe place to start but experimenting with rock plants from further afield will determine what else will succeed. Adjusting the environment by the use of berms, rocks and mulches may make a difference to how things grow. Are you interested in bulbs such as cooperias, habranthus and zephyranthes?

Best wishes for continued success,



Submitted by David Guillet on Sun, 03/27/2016 - 20:09

In reply to by Fermi

Hi Fermi,

The sudden shift to the warm, some would say hot, days of Central Texas spring have already made me little apprehensive about what lies ahead. The first of two batches of plants from Laporte Avenue and Sunscape nurseries in Colorado went in this week.  I chose plants as best I could from ecoregions of steppe terrestrial biomes elsewhere. The Edwards Plateau where I garden is located in the southern extension of the Great Plains, one of the four steppe biomes, the others being Central Asia, Patagonia, and South Africa.  The excellent new book, Steppes, put together by staff members of the Denver Botanic Garden gave me the idea to use this as a strategy in selecting plants. I put together a list of plants from the Asteraceae, Fabaceae, Onagraceae, Scrophulariaceae and other families common to this biome. I also included a few from the Mediterranean. It remains to be seen how many will be able to stand the heat. 

I've have great luck with Cooperia pedunculata and have put in some habranthus sp. 

I'm starting to think about propagation from the seed lists starting this fall to expand the possibilities.

All the best,