Wooden Planters for a Balcony: Cedar, Treated Wood and Liners

The best wooden planter for a balcony is made from a rot-resistant wood such as cedar or redwood, or from lumber treated for ground contact, with drainage holes and a liner that still lets water out. Extension services consider modern copper-based treated lumber low risk for herbs and vegetables. Avoid old CCA lumber and railroad ties.

This page covers freestanding boxes and troughs. Wooden boxes for a sill or rail are in window boxes, and if wood is not the right fit, compare metal planters or browse the balcony planters hub.

Rot-resistant woods for planter boxes

Wood in constant contact with damp potting mix will rot eventually. University of Illinois Extension says to choose cedar or redwood, which are naturally resistant to decay, and to buy from sustainable sources. University of Maryland Extension lists more decay-resistant options: black cherry, oak, black locust and Osage orange, alongside cedar and redwood.

How long a box lasts depends on the wood and how wet it stays. University of Illinois Extension notes that treated lumber lasts longer than untreated, and that wood may rot over time whatever you pick.

Wooden crates and half whiskey barrels also work as containers, University of Maryland Extension says, as long as they drain.

Is treated lumber safe for herbs and vegetables?

Modern residential treated lumber is considered low risk for food plants by the extension services that have studied it. The wood to avoid is older lumber.

• MCA and copper azole. University of Maryland Extension says MCA is now the most widely available residential preservative, contains copper but no arsenic, and is considered low in toxicity. Oregon State University Extension found that copper azole lumber raised soil copper only within about 1 inch of the bed edge, with no increase in copper in the vegetables and herbs grown.
• ACQ. University of Maryland Extension’s Home and Garden Information Center says ACQ lumber is safe to use in food gardens: some copper may leach, but the risk to human health is low.
• CCA. Lumber treated with chromated copper arsenate has not been sold for residential use since 2004, both Maryland sources say. Do not reuse old CCA boards, and Oregon State University Extension adds railroad ties to that list. Maryland also lists creosote and Penta as treatments to avoid.

Oregon State University Extension says to buy treated lumber rated for ground contact. If you are still uneasy, its advice is to choose cedar or redwood instead. University of Illinois Extension urges caution with treated lumber when you grow food or have toddlers around.

Liners and drainage in wooden planters

A liner does two jobs in a wooden box: it keeps damp mix off the wood, and it slows drying. University of Maryland Extension says porous materials such as wood and unglazed terra cotta dry out faster than plastic, resin, fiberglass or metal. University of Illinois Extension says a container can be lined with plastic to reduce water loss.

Whatever liner you use, the box still needs to drain. University of Maryland Extension says every container needs holes or slits for excess water, and suggests fiberglass window screening over the holes to keep the mix in. Cut matching holes in a plastic liner, or staple it so water can escape at the base. Gravel in the bottom does not help, the same source says.

Set the box on feet or a tray so it does not sit in runoff, which also keeps water off the balcony below. See planter saucers and drainage.

Wooden planters for herbs on a balcony

Herbs suit a wooden box that is deep enough for their roots. University of Maryland Extension lists 2 to 5 gallons as the minimum for small herbs such as basil, thyme and mint, and 5 gallons or more for large herbs such as rosemary, sage and lavender. Group herbs with similar water needs in one box. For growing tips, see growing herbs in pots.

Wooden planter weight and placement

A wooden box is heavier than a plastic one of the same size, and the damp mix inside weighs more than either. A long, deep trough of wet mix is best placed against the building wall; balcony weight limits explains who can tell you what your balcony carries. University of Illinois Extension also flags safety issues when wooden containers are hung, so mount any hanging box with hardware rated for its wet weight, and keep large boxes on the floor.