From Clementine orange boxes to vintage soda crates to wine boxes and old tool boxes, there are many fabulous wooden boxes you can find that are inexpensive or even free. Nearly all of them can be turned into quaint, interesting planter boxes for use indoors or outdoors. Turning old wooden containers into planters can make an aesthetic design statement—they are ideally suited to rustic, informal garden styles, for example. And repurposing wooden containers into planters also defines the gardener as someone who is environmentally responsible, devoted to repurposing things rather than throwing them away.
Gardening in wooden containers requires some special knowledge and technique, however.
Lead Paint Warning
While painted boxes can be gorgeous, before you use an old painted box to use as a planter, first check to see if the paint contains lead. This can be done with a simple test kit; which can be found at hardware stores, home centers, or online retailers.
It's not a good idea to grow edibles in a container coated with lead paint, because herbs and vegetables can absorb this heavy metal. And while there is no danger of direct consumption if you are growing flowers or other ornamentals that won't be eaten, there is still some environmental danger. If paint chips or peeling paint falls into the lawn or garden soil, you'll be creating long-term contamination. Lead as an element does not break down—ever. Over the years, even low levels of exposure to lead in the soil can lead to neurological damage and slowed growth in animals and humans. Children are especially vulnerable when it comes to exposure to lead.
The Best Wood for Garden Containers
Wooden boxes can last for years—even decades—if they are made from the right kind of wood and cared for properly. Cedar and redwood are known to have a natural resistance to insect and rot damage. Cypress and teak are other woods with good resistance to the elements. But even cedar and redwood can rot pretty quickly when containers are filled with damp soil and exposed to the elements. While it is usually wood decay that brings a wood planter to the end of its life, the nails and any metal hardware used to make the box can also rust and corrode when constantly exposed to the elements. Certain preparation steps and yearly maintenance can extend the life of your wooden planters, but the reality is that, when compared to plastic, cement, or clay pots, all wooden garden containers have a limited life and will eventually need to be replaced.
While you can also build rustic wooden planters from scrap wood you have on hand if you plan to use them to grow edibles, think carefully before using pressure-treated lumber. Older pressure-treated lumber used arsenic and other ingredients to prevent insect and rot damage, and the poisonous arsenic was known to be absorbed by plant roots. This type of pressure-treated lumber will be stamped with a CCA (Chromated Copper Arsenate) label, so avoid any lumber with this stamp if you are building planters for edibles. Later types of pressure-treated lumber do not contain arsenic, but although they are said to be safe when used to grow edibles, cautious gardeners generally avoid any kind of chemicals in wood containers that will be used to grow vegetables and other edibles. If your planters will be reserved only for ornamentals, though, there is no reason not to use pressure-treated wood.
Never use creosote-soaked railroad ties for any planter, no matter what you'll be growing in it. This oily preservative contains hundreds of chemicals, and even just brushing against creosote-soaked wood can lead to skin rashes and burns. This is a dangerous substance that has no place around the home in any form.
Preparing a Wooden Planter
Some controversy exists over whether wooden planters should be coated with a chemical sealer or wood preservative to extend their life. A liquid wood sealer applied to the inside and outside surfaces of a planter, then reapplied every year, will certainly extend its life. But conventional wood sealers usually contain solvents and other substances that can release hazardous chemicals into the potting soil, where it potentially can be absorbed by the plants—and eventually by any person who eats those plants. So, it is best to avoid such commercial chemical sealers for planters that will be used to grow herbs and other edibles. Planters that will hold ornamentals, though, will hold up much better if you regularly apply a wood sealer to the inside and outside surfaces.
Devoted organic gardeners may use several preservative treatments that are safer than chemical wood sealers on wood containers that will grow edibles.
- Paint-on wood treatments that contain acypetacs (a common brand name is Cuprinol) are considered safer than chemical sealers. The wood will, however, need to be retreated more often than with chemical sealers.
- Water-based preservatives based on boron salts are thought to be safe to humans; they are generally applied in paint or gel form. They do not bond well with wood, however, and may leach out, requiring frequent reapplication.
- Linseed oil is an old-time, classic wood treatment. Made from natural flaxseed, linseed oil has very good preservative properties but takes quite a long time to dry. Avoid products that are mixed with solvents such as mineral spirits, and allow the container to dry out for several weeks before planting. Use only pure linseed oil if the goal is to avoid synthetic chemicals. Be aware, too, that linseed oil is quite flammable before it dries.
A wooden box may need drainage holes, depending on how porous it is without them. Water that stands for too long in a planter will drown plants by choking out the oxygen supply to the roots, so good drainage is essential.
To determine if your planter has sufficient drainage, fill your empty box with water and see how long it takes for the water to seep out. If the water freely runs out the bottom seams of the box, no other preparation is necessary. But if the box fills up and holds water for more than a minute or so, drill some 1/2-inch drainage holes in the bottom and a few in the sides of the container, near the bottom.
Line your planter boxes porous landscape fabric. The goal here is not to prevent the wood from getting wet—that's impossible in outdoor settings—but rather to prevent the potting soil from directly contacting the wood. The porous landscape fabric will allow water to drain through the soil and out the drainage holes drilled in the box. You can also use plastic to line your pots—a preferred method for planters used indoors—but make sure you punch holes through the plastic at the drainage hole locations.
Choose plants suitable for the depth and size of your wooden box. For shallow boxes, choose shallow-rooted plants. Succulents are a great choice for shallow boxes. Also, microgreens or most salad greens will do fine in a shallow box.
Tips for Growing in Wooden Containers
Once you've decided on a wooden container and treatment, follow a few steps to ensure the success and longevity of your new planter.
- Elevate your planter boxes on pot feet or small blocks of scrap wood if they will be sitting on a wooden deck or patio surface. This will prevent trapped moisture from affecting the underlying surface, and also create space for the containers to drain.
- At the end of the growing season, empty your containers, brush out all soil, and store them in a dry place for the winter. Giving the wood a chance to dry out will greatly extend the life of your planters.
- Apply a fresh treatment of your preferred sealer regularly. Yearly reapplication of a wood sealer is the best plan if you want your planters to last a long time.
- Smaller planters will dry out faster, so monitor them frequently and water the plants when necessary. In many climates, daily watering will be necessary with any wooden planters, and small planters in the direct sun may need to be watered twice a day.
- Large containers can be very heavy. To lighten them, first fill the bottom of the planter with a fill material, such as leftover plastic bottles or a thick layer of leaves or twigs, then fill in with potting soil over the top. Most plants need no more than about 9 to 12 inches of potting soil to grow well, and your containers will be much lighter to move around if the extra space is filled a lighter material.
- Do not fill your planters with ordinary garden soil (dirt). Plants in containers grow much better with a commercial potting soil, or a make-your-own potting soil consisting of equal parts vermiculite or perlite, peat moss, and compost. Ordinary garden dirt does not have the porosity necessary for container plants to grow well, and it contains microorganisms that will rot your wooden planters fairly quickly.