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| Safe Containers for Growing Herbs and Vegetables In |
Answered by: Conrad Richter
Question from: Melanie
Posted on: April 05, 2008
I want to do some container gardening this year and want to make sure I’m planting the veggies and herbs in healthy containers. What materials are safe?
There are two aspects to this. One is what containers are safe for growing herbs and vegetables in for human use. And the other is what containers are safe for good plant growth. I suspect that you mean the first, but I will address both because they are both important for the success of any container growing project.
What materials are safe for human health? Unglazed clay, terra cotta and untreated wood are safe. Probably most plastic containers designed for horticultural use are safe. Planters made with paper and cardboard composites have been on the market for years and are probably safe. Bricks and concrete blocks are safe; so is glass. Materials to avoid are glazed pottery and treated wood products, particularly wood treated with arsenic such as the pressure-treated wood so popular these days for outdoor use. Railway ties treated with creosote are definitely to be avoided; they are not as common nowadays but they were once very popular for building raised beds. Glazed containers are mostly safe, but I would want to know more about the glazing used. Metal containers generally are okay too, but I would avoid those that are soldered together because solder contains lead.
Plants will grow fine in containers made of all of the above materials as long as the drainage is adequate. I have seen a lot of very fine looking glazed clay containers that are completely useless as planters because there are no drainage holes -- or not enough of them -- to allow free drainage of water. If pools of water persist on the surface of the soil after a heavy rain or after a through watering you have a serious drainage problem and few herbs will thrive in those waterlogged conditions.
For my money, the very best material for planters is unglazed clay. Not only is it a material that we know well from thousands of years of experience -- clay containers have been used to store grains and water safely so we know they are generally safe -- it also breathes well, allowing moisture to seep out the sides and air to enter the root zone. Plastic does not breathe, and the risk of developing waterlogged soil is much greater when plastic containers are used even when there are drainage holes at the bottom.