Monday, January 12, 2009

Hypertufa: there is no cure

I've been pretty obsessed lately.  I have been introduced to a world of cement, acrylic, and plywood, and I just cannot get enough of it!

My friend John Holm, horticulturist, former coworker, and fellow alumnus of the School of Horticulture, has taught me and my good friend and co-worker Kim,  how to make hypertufa alpine troughs.   

Before we talk about the how, let's touch on the what and the why. The trough is a shallow vessel for growing specialized rock garden plants. Being separate from the larger garden bed, a trough allows the grower to customize the soil and create an environment that does its best to replicate natural conditions for particular species. Alpines are remarkable species native to high-altitude conditions requiring very specific soil and growing conditions to survive and thrive. 

See, alpines are the little plants that could. Alpine plants survive many challenges with some pretty cool adaptations.  They cling precariously to sheer rock despite the vagaries of a windswept cliff. They survive inhuman winters (like this one) without a shiver. How?  Go ask Carlo Balistrieri about tight buns. Seriously. Alpine plant morphology is highly specialized. Leaves and stems are reduced into very specific forms enabling them to adapt and survive in harsh conditions: buns (told you), mats, and cushions make it happen. Basically it's a mini plant with HUGELY disproportionate flowers.  A big topic for another day. In the meantime, here's an alpine sunflower, Hymenoxis grandiflora, native to the peaks of Colorado

So to grow and display these tenacious gems, the gardeners of yesteryear found a new use for an old thing: the hand-hewn stone watering trough.  Left abandoned on old farms and pastures in England, these were the perfect (and very heavy) growing solution for resourceful gardeners. Charming in all the right ways, these containers have been worn, weathered and adorned with lichens and mosses. Finding these originals today is possible, but will require you to either a.) give up your firstborn, or b.) hand over a small fortune, neither of which I have.

But HYPERTUFA!!  Ahhh, hypertufa.  Lightweight, frost-resistant, and a deceptively accurate substitution for those lacking progeny or profit.  So when John invited us to come over to get our hands dirty, how could I resist? 

It was late December when John showed us how to construct forms, proportion a good mix, and how to prepare, pack, and cure a proper trough. John had set up a very functional work space in the basement of the greenhouse; he is a very neat guy, and this is a very messy process. 

After the work space is ready, make some molds. This is 2" thick insulation board.  It's easy to score and cut to whatever dimension you want to make.

Longs nails are pushed into the sides, and duct tape is wrapped around the mold for stability.

Secure the mold to the table so it doesn't shift while packing in the hypertufa mix.

Here is one way of making sure drainage holes are present. John uses PVC piping cut to the thickness he wants the bottom to be.

Here's the mix:  peat moss, perlite,Portland cement and plastic fibers (last two can be located at a masonry shop).  The proportions differ from person to person.  Like any recipe, really. To make one "batch" John uses 12 parts peat and perlite, 8 parts cement, and a handful of fluffed fibers. Just as in baking, thoroughly mix all the dry ingredients together before adding any liquid.

Add water and liquid acrylic.  Use a 1:1 ratio of water to acrylic, then add more water to reach the desired consistency.  Think cottage cheese, but a touch drier. Once you have that down, time to pack!  Pack in the bottom and corners really well.  This stuff has to be very densely packed down, otherwise the integrity of the container can be compromised.  

And when you are done, it should look like this! My very first hypertufa trough.  I was so proud! The walls should be thick; no less than 1.5".

So now wrap it in plastic and store it at about 60F for 24 hours.  This is the first cure.  

When you return to the trough, you can unwrap it and "finish" it.  Literally, put a finish on it. Scratch it, scrape it, abuse it . . . anything that will add to the weathered worn feel that would otherwise take many long seasons to accomplish.  When you have finished, spritz the entire container with water, cover it, and let it sit for one month.  This is the second cure.

When you return after a month, unwrap it, and allow it to sit uncovered outside.  This allows the alkaline and caustic qualities of the cement to dissipate prior to planting.  This can take a couple months.  That is the final cure.

It seems tedious, but once you have a system, it all goes quite smoothly.

How will I use what I learned here? Me being me, I cannot just limit this craft of trough-making to the narrow usage of alpine troughs.  Traditionally, the hypertufa container is made for growing alpine plants. But I am always looking for ways to give a fresh face to a familiar facet. 

If you'd like more details, check out this book Creating and Planting Garden Troughs, by Joyce Fingerhut and Rex Murfitt.  Essentially the trough bible. 

In the meantime, my troughs are wrapped and waiting. Stay tuned for photos of the finished results!!! 


  1. Great post. Is there a bottom to the form, or is that just plywood covered with plastic sheeting? Also, do you need some type of release agent to separate the Tufa from the foamboard - plastic sheeting, cooking spray? Or is the pink board safe?

  2. Oh my God I just love this trough. Wondering though, is the moss growing on the outside natural? It certainly looks like it has been outside and aging for a long time. Was it put into the shade? Linda Nelson