Place your choice of cylinder object in the planter 1st, then pour the concrete around it, or, fill the planter with concrete 1st and then press the cylinder object directly down into the concrete, squishing the concrete from the bottom up the sides of the planter, creating a perfect hole while creating an uneven edge.

Thinking out of the box, why not separate the concrete into 2 or 3 uneven amounts and color each differently, depending on the color and/or choice of plant. Layer the colors, press the cylinder object into the colored layers, and in doing so, the combo of the colored concrete layers and squishing each colored layer upward will create a mesh of the colors and swirled art. Another idea would be to use a toothpick, skewer, pencil or knife, and run it along the inside of the planter wall and concrete, pushing downward. This leaves more of an uneven, freehand and swirly mesh of the colored layers. Which is pretty cool.

Believe it or not, brown or green moss would sustain itself on top of the concrete, adding more color.

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-Becca
Ladyface Blog