There are many variations of rock plantings, but I recommend the basic "Root-Over-Rock" as it is amongst the most attractive and the easiest to maintain on a long-term basis. Hawaiian lava cinder is the ideal rock for beginners as some existing character can be greatly enhanced by many shaping methods that could include chipping with a pick, using a hammer and stone chisels,  drilling with masonry bits, cutting with stone saws to create a flat bottom,  or using colored matching concrete to hold a vertical rock in position. 

        Hawaiian cinder rock is porous with some surface texture.  Selected rocks may start out like the two outer ones. The center rock is shown after being shaped.  Rock carving can take many hours for larger pieces.  The bottom of the center rock was placed on a "concrete pancake" and finished to keep the rock sturdily in a vertical position.  
         The two rocks on the wood blocks were shaped with a hand drill with a masonry bit to create character while the selected rock on the bottom has not had any work done yet.  A "saddle" or mounting position was selected and "root trails" were carved to guide the roots down from the saddle to the media in the pot below.

         The bottom has been trimmed to allow the rock to stay in a more interesting upright position.  Note that holes have been drilled right through near the bottom so a wire can securely anchor the rock to a pot.  

               A close-up view of the right rock in the photo above.  This has a deep saddle that will allow the roots to lock onto the rock.  Several "root trails" were carved with a drill with masonry bit to guide the roots to the media in the pot.  Generally roots are more attractive when they are slightly depressed into the rock.  Round roots sitting on the surface of a very dense rock are not attractive. 

        Finding suitable rocks is very time consuming and it takes a practiced eye to sort through and select the most useable pieces.  I have never found a "perfect rock" and rock sculpturing is hard work!  Our staff uses size gauges to assure that rocks for our Hawaiian Lava Plantings meet both minimum and maximum size (and weight) standards. 

       We are creating larger root-over-rock specimens for the Custom Collection.  Trials have been in progress for almost twenty years and this article incorporates some of the improvements that we've learned since we began the trials.

       In bonsai,  vertical rocks are visually most interesting and suggests cliffs and steep mountains.  

        The first step is to line all "root trails" with a thin layer of damp sphagnum moss.  This provides a water moisture distribution material that roots like. It is better to have deeper root trails to allow a fair amount of sphagum moss,  body media, and Nutrient Granules. 

       Follow with a layer of body media screened through a 1/4" mesh to remove the larger pieces

       Note the white particles are Nutrient Granules that are embedded in the root trails.  Alternate a layer of body media followed by the sphagnum moss and repeat until the "saddle" is completely covered and  is 1/2" to 1" higher than the final height where the plant will be sitting.
       Once the rock is prepared, remove the plant from the pot, untangle and separate the roots so each section drops straight down.  By now you know which side of the rock has the deepest and most root trails and I tend to place the largest roots on that side. 

      Go up into the bottom of the root ball and if there are a generous amount of side roots, you can be more aggressive in removing roots under the trunk that will go right onto the saddle. 

         Place the tree firmly on the saddle and push it back and forth until it is solidly seated.   I like to use paper covered thin wire over the tree and under the rock to pull the tree down.  Once secured, the tree will not ever move again and you should be able to pick up the tree and rock by lifting the trunk. 

        This is the hardest part of the entire effort.  I prefer not to bare-root the plant to get an idea of the root system first.  If you start working on the rock after checking the roots, the tree will dry out.  It's better to have a lot of extra root valleys already complete before starting to plant!

         Once the largest root is in position, find the second largest root and guide it down a second root trail.  If the valley is a little shallow, place some sphagnum moss on that spot before locking the root in place with the paper coated wire.  If you have four or five major roots,  I may go up, around, and under the rock four or five times to have all major roots stretched and secured into the root trails.  With a dibble,  you can compress the roots.  Try to expose as much attractive rock details as possible. 
          Then starting from the top, secure all roots into position with the paper covered wire crossing each of the root trails while keeping much of the rock from being covered with roots.  Note the hole on the bottom is kept cleared for a wire to go through to anchor the planting to the pot.
      Send the anchor wire through the hole, bend it down on both sides, and mark which of the bottom holes the anchor wires will go through to position the rock planting at the most attractive position. 
       To form an aluminum foil collar, tear off a sheet  long enough to go almost twice around thr rock planting.  Fold in half for a double thickness of the 12" wide foil.  Starting from one end of the 6" wide foil, make a series of "accordion folds" about 1/2" wide.  Then turn and partially open so all folds are about even.
       In early efforts,  I had a thick layer of body media covering all of the rock and the roots but found that when cleaning the excess media off, that there were a lot of "floating roots" that needed to be removed. With the accordion fold method,  vertical channels are created and it is more likely that the roots will be running up and down and be retained.
        Place body media on the aluminum foil and place the rock planting on it so the trunks are even with the top of the foil and the foil reaches at least to the bottom of the rock.
         Carefully lift the left side of the foil so that the media on it comes in contact with the rock.  Add a little body media to the top of the rock.  Then carefully lift the right side of the foil, line up to two ends,  and fold over the edges a few times to complete making a foil column around the rock planting.
       Choke the aluminum foil firmly against the neck first to secure the media near the top and work your way down so the foil column is now tightly against the rock with the anchoring wires sticking out.

        Fold the aluminum foil "skirt" up so about 1" of the bottom of the rock is exposed.  Note that some body media is between the rock and the foil, but that the foil is holding the media tight against the rock.

         Thread the two anchor wires through the two marked bottom holes.  Press down and bend the wires so the rock planting is snuggly against the pot and it is possible to pick all up by lifting the rock planting.

         Fill half of the depth of the pot with coarse bottom and firm it into place.  Add body media to within 1/4" of the top of the pot rim and firm it into place.  Add a little top dressing to complete potting. 

            Although this may seem complex, with practice, it is done very quickly and the plant does not have a chance to dry out.  The root hook is very efficient in separating the roots and if work is done carefully,  there is minimal loss of even the root hairs.  Roots are quickly placed over damp sphagnum moss and covered lightly with body media held in place with the foil column. 

           The top of the foil is bent outwards to form a water catching funnel to make watering easier.  Air holes are poked through the aluminum foil every half inch.  The leaves are fresh and seem ready to resume growth.  A few older leaves were removed and the plant given it's first watering by soaking with some sent down the water funnel. 

           We have used various foil methods for twenty years and continue to learn more effective techniques.  It's a great technique that makes root-over-rock plantings very easy with a very high success rate.  None of our rock plantings die at Fuku-Bonsai since learning the aluminum foil techniques. 

    ***  Return to the August issue of Journal of Tropical & True Indoor Bonsai
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           Mid-Pacific Bonsai Foundation & Fuku-Bonsai, 2013