Stéphanie wrote to me a few weeks ago to ask whether it was dangerous to put Styrofoam in the bottom of a garden box, given that it’s a petroleum product known to be harmful to the environment.
Indeed, I’ve seen this recommendation on the internet several times myself, and I’ve even tried it! But is it dangerous to eat tomatoes grown in a vat containing petroleum? Aren’t you lucky to have a biologist among your favorite Internet stars who knows the answer?
Basically, the Styrofoam (or polystyrene) in the bottom of garden containers is not at all dangerous for your plants, and you can safely eat the vegetables and herbs that grow there. BUT! It’s downright unpleasant for the gardener to work with, as well as being… completely useless!
Is Petroleum Dangerous For Humans?
These are strange times. Certain environmental currents share all sorts of warnings and vehemently denounce… well… just about everything…
We should be vegan, import nothing, stop monoculture avocado farming, denounce the droughts caused by cashew nut cultivation, wear only natural fibers, buy organic, ride a bike, stop hunting… In short, it’s easy to denounce anything and everything. And it’s very difficult to differentiate what’s true from what could be nuanced, or even absolutely false.
Here’s The Truth About Petroleum Products…
… you use them every day and it’s impossible to save yourself. TAN TAN!!! (dramatic music)
In fact, many of our objects and products are made from petroleum by-products. Reheating your lunch in a plastic dish? Petroleum. Does your blender make great smoothies? Petroleum. Do you wear lipstick? Petroleum. Sunscreen? Petroleum. Love scented candles? Petroleum. Ibuprofen, aspirin, cough syrup? Petroleum!
(By the way, chances are your plastic garden container contains petroleum too!)
Yes, there’s oil in just about everything! Strictly speaking, it’s not dangerous for humans. Some chemical compounds can be, don’t get me wrong! If you burn plastic, it stinks, and these compounds are bad for your health. But will we “die of oil” if we use it safely and normally? No.
What is petroleum, anyway? Quite simply, very, very old compost that has been transformed into a kind of oil that humans have learned to transform in many different ways. Oil is therefore a “natural” product that we chemically transform to obtain fuels, plastics, cosmetic oils, handicrafts… and anything else we can think of!
Polystyrene, Dangerous For The Environment
Back to our styrofoam. The environmentalists who will tell you that plastic is bad don’t always understand why. No, it’s not because of the oil or even the manufacturing process! It’s at the end-of-life stage that plastics, including styrofoam, become a nuisance. Dear No. 6, as it’s known in the recycling system, has long been banned from the blue bin, and still is in many municipalities.
In recent years, it has slowly but surely begun to be accepted by some sorting centers. In fact, styrofoam is very easy to recycle: it is dissolved, then the liquid is removed from the solution and the plastic can be reshaped. The trouble is, “new” is so easy to make that it costs companies less, so few of them source recycled Styrofoam. 80% of the #6 put into recycling inevitably ends up in landfill. And therein lies the real problem with this expensive material.
A Long Decomposition
You see, this plastic takes some 1,000 years, sometimes more, to decompose. Like all waste, it produces greenhouse gases as it decomposes. These are not bad for humans, but they are responsible for the global rise in temperature.
Oh, and by the way, those “it takes 1000 years to decompose” stories are more or less false, too. It takes that long to stop looking like a piece of plastic, but many of these materials simply break down into microparticles that end up in the oceans. Okay, the plastic is no longer visible, but it’s still there.
Marine creatures eat or “breathe” in these pieces of plastic, and they remain trapped in their bodies. The birds that eat these fish, turtles, snails, shrimps, etc., in turn end up with plastic in their bodies. If these particles don’t break down, they don’t digest either. They remain trapped in the animal, filling its stomach and lungs and gradually impairing its vital functions. Being hungry, but unable to eat because its stomach is full of undigestible matter, that’s the danger of plastic.
I digress, but I think it’s important to explain why plastic (or petroleum) is considered harmful to the environment, but not to humans. But with all that, the gardener who puts styrofoam in his plants will be reassured: unless he grows the same styrofoam for hundreds of years, it won’t even begin to degrade! And since plants don’t absorb microplastics, they’re a fairly targeted threat to animals, especially marine ones.
To Drain Or Not To Drain?
The reality is that a drainage layer is often unnecessary. Before you even think about putting a layer of plastic in your herbs, ask yourself if it’s necessary. Is there a hole under your planter? Is it a bottomless planter on the ground? If so, you don’t need a drainage layer. If not… make a hole and you’ll have drainage!
Not draining enough? Perhaps your soil is the problem: choose a lighter potting soil or mix in sand, dead leaves or wood shavings (carbon-rich compost), and you’re in business when it comes to drainage.
Some special cases require a drainage layer, but personally, I find it a bundle of trouble for a Laidback gardener, as well as being a roll of the dice. In a planter with no holes and a drainage layer, excess water cannot disappear: it stays at the bottom of the pot. This water keeps the soil at the bottom moist, making the roots there rot, while the rest of the soil needs to be watered again… Little by little, your plant will dry out as root rot spreads, preventing it from drinking from the roots, no matter how much water is available…
But if you really want it, give it a try, and be careful not to overwater!
The Styrofoam Layer
Having already tried it, I hated it! It was my first plant. I had a big pot with a hole in it, and I thought to myself: my plant is tiny, it doesn’t need all this space! I’ll save on the soil and put some Styrofoam in half the pot!
R.I.P. my first aloe.
There were a lot of bad things about this reasoning, but I still learned a lot. It didn’t stop me from killing other aloes, but that’s not the point!
Because Styrofoam is so light, the jar fell over ALL THE TIME. I don’t need to tell you about the damage… A full bowl is much more pourable than a glass one, because the weight is higher up. This is exactly what happens with your planter. When the wind blows through its large leaves, it’s liable to topple over.
Then, when I unpacked my pot, separating the soil from the Styrofoam was hell. I compost my old soil: I paid for it, I’m not going to throw it away, I’m going to recover it! And no kidding, I still find pieces of that Styrofoam in my garden (where I put my compost) six years later.
In short, nowadays, if I need to save soil, I put bits of wood, which will become compost, or rocks, to weigh down my pots and keep them upright even when it’s windy. Not because Styrofoam is dangerous (some potting soils contain it instead of perlite!), but because it’s neither useful nor pleasant to work with.
Go in peace, my dear gardeners, with or without styrofoam!
Early in my gardening life, I also used styrofoam peanuts in a large container. I had the same issues. The pot was top heavy and fell over easily. The following year I decided to remove the styrofoam. I thought I was smart when I wrapped the stuff in plastic grocery bags. But the bags had become brittle and tore, mixing the peanuts with what should have been good soil. Never again.
Excellent explanation
I found it helpful to minimize the weight of very large patio pots. But, yes, emptying the pots at the end of the season, and gathering the Styrofoam pellets to reuse, was an awful task. I have learned that a piece of landscape landscape between the soil and the pellets will improve the situation, but not much. I no longer use Styrofoam.