Before you start potting, check out the box you’re using to make sure it won’t seep anything dangerous into the soil and your edibles
May 4, 2017
Think twice before you decide what containers to put your plants in, particularly when it comes to edibles. Why? The very same properties that make soil a perfect channel for nutrients and water to find their way into plants also make it a channel for harmful toxins, especially ones that are hiding inside the pots and vessels holding the soil itself.
Here’s what to avoid and what’s safe to use:
Lightweight, and nearly indestructible, plastics have been the magic answer to a myriad of storage, transportation, and packaging dilemmas. Our world is swimming in plastics, and when we get the chance, it’s nice to be able to recycle them. But many plastics— particularly when they’re exposed to sunlight, water, and high temperatures—leach toxic chemicals like bis-phenol A (or BPA), vinyl chloride, or phthalates (a salt or ester of phthalic acid) which are hazardous to human health. Higher density plastics, such as those used to make yogurt pots, soda bottles, and rigid containers like cups, bowls, and planting pots are more stable, and therefore safer to use.
Ceramic Possibly the classiest choice for a planter, ceramic is practical as well. It’s durable, breathable, and generally made from natural ingredients (mostly clay). Ceramic has its own suite of challenges for the container gardener, but transferring harmful substances is, thankfully, not one of them—unless you opt for glazed ceramics. Colorful, glossy ceramic pots are coated with glazes that may contain lead oxides.
A good choice: Self Watering Terracotta Planter
Wood An untreated wooden box is an excellent container for edibles except for the fact that, given time, it will rot. Slap on some stain or preservative paint, and things start to get complicated. Many wooden containers sold to gardeners are pressure treated to increase their lifespan and ability to stand up to moisture. The chemicals forced into wood during the pressure treating process (copper, chromium, and arsenic—also known as CCA) arrest decay and generally don’t leach into soils much after the first initial rain. Arsenic isn’t something you want to build up in your garden soil, however. To minimize any chemical movement, scrub or power wash wood prior to usage. Older, salvaged wood containers like whiskey barrels or window boxes have also usually been treated with CCA. If you’re working with a more fragile, antique container, add a plastic liner before planting to keep any residual leaching in check. If you choose to decorate your own wooden container, select paints, glazes, or oils that are marked with a nontoxic label. Prior to the 1980s, use of lead paint was widespread—particularly on outdoor surfaces exposed to wind, sun, and rain. Lead paint will chip and flake as it ages, letting it dissolve into soil, so a good way to assess whether that antique bucket has been coated in it is to look for lead paint’s characteristic cracking pattern. To go completely 'au naturel', use wood that is rot resistant and requires no treatment at all: Cedar is the perfect pick.
A good choice: Copper Garden Trowel
Rubber Old tires have become a popular, salvageable item for growing root vegetables like potatoes and carrots. They stack easily, are free, and help warm the soil in the chilly months of spring. However, as tires age they release a litany of toxic compounds into the ground—including carcinogenic hydrocarbons. If you’re looking for a quick and dirty way to start growing spuds, trying using a grow bag. They offer the same no-digging-required perks of tires but are made from nontoxic (and often recycled) materials.
Metal A safe pick is metal. It’s true that in humid, moist climes, pots can quickly rust, but the oxidized metal doesn’t leach into the soil the same way lead does. If using a galvanized metal container (such as an old wash tub, trash can, tool box, etc) be careful: zinc (an essential nutrient) and cadmium (a toxic heavy metal) can leach into the soil when it's exposed to the right acidic conditions. If in doubt, use a plastic liner or nest a ceramic pot inside the metal container.
Foam Foam trays can be recycled from fishmongers and grocery stores and are a great way to start seedlings. They create an excellent well-insulated environment for young and tender plant roots—provided additional drainage holes are added to trays. It’s true that styrene, one of the ingredients in foam, is listed by the National Institute of Health as a carcinogen. But it takes a long time to degrade (somewhere in the order of hundreds and hundreds of years) and does not easily break down when exposed to water, air, or dirt. So seedlings will do just fine in it.