Concrete planters are made using a small container and a large container as molds. How far you push in the interior container will affect the thickness of the walls of your finished concrete planter. Once finished, the foliage and bright blooms of your plants create vivid contrast with the textured gray container.
These projects are excerpted from Concrete Garden Projects, by Malin Nilsson and Camilla Arvidsson (Timber Press, available through Amazon.com).
To make a concrete planter, choose two containers to use as molds. Use a paintbrush to thoroughly coat the inside of the larger mold with cooking oil.
Use a paintbrush to thoroughly coat the outside of the smaller mold with cooking oil.
Fill the larger mold with concrete to about 1 inch from the top. Shake to eliminate air bubbles; level the surface.
Push the smaller mold into the center of the concrete, leaving an adequate thickness for the bottom of the planter.
Place a weight in the smaller mold and let the concrete set for 24 to 48 hours.
Gently remove the molds. Smooth rough and sharp edges with a stone or file.
Choose container shapes that complement your garden's style, and make sure plants will have a suitable container in which to thrive. Drill drainage holes into your planters after the concrete has set, or place a cork or piece of foam in the bottom when forming the pots. When you water concrete planters, they will darken, then lighten as they dry.
Because candleholders typically are small, they are good practice projects for working with concrete. Try using empty yogurt containers or margarine tubs as molds. Before the concrete for a candleholder sets, oil a candle and insert it in the concrete to get the right fit. (Clean the oil off the candle before lighting.)
Concrete DIY planters are extremely adaptable in terms of style: Use fluted forms to fit with cottage-inspired garden furniture, or choose straight lines and geometric shapes for a more modernistic look. Plant with a few bulbs for early blooms in springtime; transition to colorful annuals in summer and autumn. Be sure to push your interior mold down far enough so the inside gives plants room to root. If you don't want to see the soil in the planter, use small rocks as a mulch to complement the concrete material.
To create a birdbath rather than a planter, use a wide, shallow interior container. For a more organic form, simply press a shallow impression into the concrete. For regular patterning, select a few similarly shaped rocks; oil them and press them into the wet concrete. Look for castoff bits to use as decoration, such as small mirrors that can be embedded in the bottom of the bowl to add reflection to the water.
Once you've mastered smaller projects, consider moving on to larger pieces, such as a concrete bench. For a simple design such as this, use plywood and framing pieces to make a mold. The finished bench will be heavy so it likely will need a permanent site. Toss on a few cushions to use it for seating, or make it a spot to display potted plants.