The purpose of the gravel or pebble layer in a terrarium is to provide drainage and prevent the plant roots from sitting in water and causing rot and death to the plants. We can make our own edible river rocks for our terrarium using model chocolate, Oreo crumbs, food coloring, and cocoa powder.

Candy Clay/Modeling Chocolate

White and green colored candy melts (preferably two different shades of greens, one sage and the other more puce green)

Corn syrup

Plastic wrap

I had two different green colors of candy melts in my cupboard, so I decided to make two different shades of green modeling chocolate (also known as "candy clay" since I am using candy melts instead of actual chocolate). Not pictured, but very much needed for the chocolate pebbles process, is white modeling chocolate, so make sure you whip up a batch of white as well.

For every 4 ounces of candy melts, you will need 1 ounce of corn syrup. I had 12 ounces of both the green candy melts, so I used 3 ounces of corn syrup each to make them into modeling chocolate. I only had 8 ounces of the white candy melts, so I used 2 ounces of the corn syrup.

Heat up the candy melts just to the melting point, or else they will overheat and be unusable if you are not careful. This usually means short bursts in the microwave (30 seconds or less at half power) and lots of stirring to evenly distribute the heat. When completely smooth and melted, pour the corn syrup on top of the melted chocolate. With a slow folding-like and squishing motion, stir the mixture to make sure the corn syrup has come into contact with--and seized--all the chocolate. By stroke number 25, the modeling chocolate is becoming a ball that will not stick to the sides of the bowl anymore. By stroke number 26, you have overworked the modeling chocolate and it is releasing its oils now--stop! STOP!

But seriously, it is a fine line between underworked modeling chocolate, with bits of hard chocolate in the mix that never came in contact with the corn syrup, and overworked modeling chocolate, floating in an oily pool. I like to error on the side of overworked, rather than underworked modeling chocolate, because I can't stand the hard bits of un-seized chocolate floating around in my smooth clay. So when I come to the point of the chocolate releasing its oils when I am stirring it around, I pour off the excess oil down the drain and wrap the remaining candy clay in plastic wrap to rest overnight. In the morning, it will be hard as a rock, but with enough kneading, it transforms into smooth modeling chocolate that is perfect to work with!

Even if your modeling chocolate turns out to contain little bits of chocolate after kneading it in the morning, don't despair! If you are only using the modeling chocolate for rocks and moss, it will still work even if it is a chunky-monkey. Modeling the succulent plant probably won't go so well, however, so you might need to make another batch or use fondant in that case.

Candy River Rocks

White modeling chocolate

Food coloring (gels, candy coloring, or even liquid food dyes all work)

Crushed Oreo crumbs

Cocoa powder

Pinch off 3 to 4 golf-ball sized chunks of white modeling chocolate to color with your choice of food colors. (I used pink, blue, purple, and grabbed a piece of my green modeling chocolate instead of coloring another section green.) Splitting each colored section into two balls, dip them into different colors of cocoa or mix different amounts of Oreo crumbs in it to now get eight differently colored candy clay balls. If you need to add a touch more food color to some sections to make them stand out more, go ahead. Pinching off small amounts of the clay in your fingers, roll it around and form irregular pebble-looking shapes. Let them harden on plastic wrap on top of a cookie sheet. Put the chocolate candy rocks into your mason jars on top of the charcoal bits.

For the non-baker: You can sometimes find candy river rocks in specialty candy cake stores or else purchase it online.