Turning a wood box into a planter is a fun project, but if you don't take a few precautions, the box will get wet, and the wood will start to rot. Want to have your homemade planter last as long as possible? Then check out these ideas:
1. Paint the box.
Paint helps to seal wood from moisture and sunlight, and it can help your box last longer. Sand the box before painting it so that the paint adheres readily to the box, and if possible, choose paint designed for outdoor use.
If you find a wood box that is already painted, you can use that as your planter if you like, but if it's old, you need to make sure that the paint doesn't have lead in it. You can buy lead testing strips at most hardware stores.
If the paint has lead, do not scrape it, as that will release lead particles into the air. Simply paint over it to seal in the toxins -- wear a respirator while you work and keep kids and animals away from the box until the lead has been sealed.
2. Line the box with waterproof plastic.
In addition to or in lieu of paint, you can protect the box from wet soil by lining it with heavy duty waterproof plastic. Simply push a sheet of plastic into the box, staple it in place and trim the excess plastic.
To allow some drainage, drill holes through both the bottom of the plastic and the bottom of the box. If you use the planter inside, place a plastic tray or a mat under it to catch excess drips of water.
3. Use rocks for soil drainage and box protection.
Some gardeners don't like to use plastic because they worry about it leaching into the soil. If you fall into that category, you may prefer to use an unlined box. In this case, if you want your box turned planter to last as long as possible, you need to think of other ways to keep the wet soil away from the vulnerable wood.
Rocks are one option. Take a layer of rocks and fill the base of your box. Use a mixture of gravel and medium sized stones. Then, pour in your soil on top of the rocks. The gravel prevents the soil from migrating into the rocks, and both the gravel and the rocks help with drainage.
To explain, if the soil has excess water, it trickles down into the rocks and out through the drainage holes in the bottom of the planter. The wood box still comes into contact with some moisture, but it doesn't get as much exposure as it would if the soil were sitting directly on the wood all the time.
If you want to line the entire box with rocks so that the bottom and the sides of it are protected from moisture, fashion a smaller box made of chicken wire or other wire mesh. This should also be open on the top. Like your wooden box, it should have a floor and four sides.
Place a layer of rocks in the bottom of the wooden box, and put your wire box on top of that. Now, in the spaces between the sides of the wire mesh and the sides of your wooden box, add more rocks. Ultimately, you should have a small metal box (filled with soil and plants) inside a wooden box, with a layer of rocks in the cavity between the wood and the wire.
4. Choose a box made of hardwoods.
If you don't want to paint the box, line it or fill it with rocks, consider choosing a box that promises to stand the test of time. Hardwoods like balsa tend to last much longer than softwoods like pine. In fact, some untreated hardwoods can last up to 20 years.
Talk with a box seller in your area, like Westend Pallets (Aust) Pty Ltd, and ask them which hardwood boxes they have available. These boxes will last longer as planters than boxes made of softwood.