Making Bonsai Muck  by Ken Goebel
(Printed in MBS Newsletter May 2012)

Muck is another important "soil" mixture with many applications in bonsai.  It is a sticky paste that's used as a binding agent to hold objects such as rocks
stable in the pot.  When planting seedlings or cuttings with delicate roots, it can be wrapped around the roots to anchor the tree in the pot until the tree’s
roots are established.  This is especially useful when wiring the roots is not an option.  When we use a tray, rock slab, or cement slab instead of a pot,
muck is often used to create an edge that will prevent the soil mixture from sliding or washing off.   Muck also seems to be the only type of soil that compact
mosses adhere to and thrive on naturally.

Recipe:  The main ingredients of bonsai muck are organic fines from peat moss or pine bark, potter’s clay, chopped sphagnum moss, and water.  
Horticultural vermiculite has a basic pH of 7-9 due to associated carbonates, and the fines can be added to make a basic muck.  Fines are the powdery
components that sift through a very fine mesh screen (less than 1/16th inch mesh size), such as mosquito screening.
There are three general categories of muck:
Minor variations of these recipes will work just as well, and allows one to experiment with making muck.  One option is to add an additional
1 part of humus or black gardening dirt to the mix to add nutrients.  A good choice for potter’s clay is kaolin clay (pH 6).  Acidic muck is suitable for acid-
loving trees like azaleas and conifers.    Neutral muck is suitable for trees such as boxwoods, cedars, elms and maples.  And basic muck works well for trees
like pomegranate and crabapple.  Bentonite clay (pH 8) can be used in place of potter’s clay and vermiculite in basic muck.

Directions:  Dry mix the ingredients, then add just enough water in small increments that the muck can be kneaded to a dough-like consistency.  The
water can contain a small amount of vitamins and minerals (2 drops Superthrive and 2 drops Micrototal per quart of tapwater), if it is desired to add
nutrients to the muck.  The chopped sphagnum moss acts as a binding agent to reinforce the muck and allows it to maintain its shape.  The important thing
is to create a muck that does not crack when it becomes partially dry.  The photo shows river banks built up with acidic muck, and mounded muck to anchor
the two vertical rocks inside a saikei tray.
If you are using akadama or kanuma clays in your bonsai soil mixes, keep the sifted fines from these, as they can be used for the clay component in muck,
in addition to potter’s clay.  Akadama is a neutral pH clay, so akadama fines can be used to replace the potter’s clay.

A problem with peat moss is that when it becomes dry, it is almost impossible to re-wet, and the muck becomes hard to shape.  An alternate
acidic muck
that avoids this problem replaces the potter’s clay with kanuma fines, and replaces the peat moss with pine bark in the recipe.  Kanuma is an acidic clay
with pH 4.5-5.5, much like the acidity of peat moss.
Storage: If you have any left over, store it in a zip lock bag in your freezer.  This will keep it from becoming moldy.  When you need it for your next project
just remove from the freezer, let it thaw, add a bit more water if needed, and then knead it a bit to get it flexible and ready for use.