Cast Your Garden in Concrete

Connie Holland
Adams County Master Gardener

Now is the perfect time to preserve beautiful leaf specimens by casting them in concrete. The basic process involves covering an upside down leaf with concrete, letting it harden and cure to create a sturdy leaf casting with interesting veining. Concrete cast leaves make great eye-catching garden decorations and can be left "natural", colorfully painted with acrylics, or color-washed for a more subtle look. They are easy to make. Heavily veined leaves such as rhubarb, hosta, caladium, castor bean, zucchini, or elephant ear are good for casting. Look at the underside of a leaf for distinctive veining since that pattern will be the top side of the cast leaf. Start with smaller leaves to practice the technique. My rhubarb leaf casting is over five years old and stays outside year-round looking great in my garden on a rock wall.

Concrete used for leaf casting is a mixture of Portland cement and fine sand. One can make casting concrete using equal parts of Portland cement and sand or buy premixed concrete. It is important to use a "sand-mix" only concrete and not an aggregate mix as that contains stones that will mar a casting. (Note: there are other recipes for leaf casting, this approach has worked well in my experience.)

Supplies: One bag pre-mixed sand-mix concrete, not gravel or stone aggregate mix, and water. One bag can make 2-3 castings depending upon leaf size used. If mixing own concrete, use equal parts of Portland cement and play sand. Note: cement and resulting concrete are caustic and cementís dry dust is hazardous. Wear a dust mask when handling dry and use sturdy rubber gloves such as dishwashing gloves (not disposable gloves) at all times. Mix in a wheelbarrow or plastic masonís tub (mix can leave a residue on tools and mixing tub). Use hoe or shovel for mixing and add optional, but highly recommended, liquid Concrete Bonding Adhesive. Also needed are plastic for covering finished casting and enough extra play sand to support the concrete leaf casting during the molding process. Work on a protected surface or piece of plywood larger than the sand mound.

Note: The curing concrete leaf on its sand mound must sit undisturbed for 3-4 days out of direct sun so plan ahead and be patient. Curing correctly takes time.

Directions: Mound wet sand (sand castle wetness) into a pile 2-3" wider and taller than leaf on a protected work surface or piece of plywood. If you want a bowl shaped leaf, make a bowl shaped sand mound that fits the upside down leaf profile. If you want a flat concrete leaf, make the sand mound flat. Prepare concrete mix: Wearing dust mask and gloves, carefully add water making a very thick mud pie consistency. Too much water and mix will run off leaf so error on the side of too little versus too much. If mix is too runny, add more dry cement. The optional one-half cup of concrete bonding adhesive should be added with first water addition. Casting can be made without bonding adhesive; however, its addition strengthens casting and helps avoid cracking.

Carefully place handfuls of cement mixture on upside down leaf. Pat each addition smooth gently to avoid tearing leaf, remove air bubbles, and ensure good leaf contact for maximum veining. Spread concrete to the leaf edges, making sure outside edges at least 1" thick. Build up entire casting to 1Ĺ -2" thickness in center tapering to 1" thickness at edge. Make sure the outside edges are neat, smooth, rounded, and at least 1" thick to avoid edge cracking when dry.

If a small pedestal base is desired, form a suitable sized flat topped mound of concrete in the center to serve as the base when casting is turned right side up. Cover casting loosely with plastic. Uncover and mist daily with water for at least three days to cure concrete properly and avoid cracking. After three days, uncover and slowly lift leaf casting off of sand mound. Let cure 4-5 more days before handling. Casting is fragile until concrete is fully cured. Be patient. Dried leaf residues may be stuck in the casting veins. After fully curing, stiff brush or wash off residue with strong hose stream. It can take a few days for thick leaf residues to dry out in the veining. Castings can be left outside and will withstand winter temperatures.

A concrete leaf casting should cure for about two weeks before painting. After fully curing, castings can be painted with acrylics, stained, or sealed with concrete sealer or paraffin wax. Sealing is essential for a casting to hold water if it is intended as a birdbath. Try your hand at concrete leaf casting and create a great garden decoration.

Read other articles by Connie Holland