FAQ: Can I Grow Plants In Polystyrene (Styrofoam) Boxes? Someone Told Me They Are Toxic.

strawberry 'Red Gauntlet' in styrofoam boxes - 2
During the floods of 2011, 2012, 2013 I didn’t lose a single strawberry.


If you endorse the reuse of waste, visit your greengrocer and get some polystyrene, aka styrofoam, vegetable packing boxes. Their different sizes make them suitable for a range of gardening jobs wherever you garden. The re-use, re-purposing and up-cycling of these boxes means you can avoid buying water-saving containers for plants, plant propagators, seed boxes and worm farms, reducing your ecological footprint in the process. Are you up for good gardening and joined up thinking?

This blog looks at ways to convert expanded polystyrene foam boxes, a single use plastic used for packing vegetables, into a useful gardening asset.

Polystyrene
Polystyrene (Wikipedia).

Most Australians call expanded polystyrene foam styrofoam, but this is a trademark name, owned by Dow Chemicals, who claim to have ‘discovered’ this product which was first made in Sweden.

If you endorse waste reduction and the conservation of finite resources, visit your supermarket or greengrocer and get some polystyrene vegetable packing boxes. Retailers are happy to give them away or sell them for a couple of dollars. You’ll find them suitable for a range of gardening jobs.

I started using polystyrene foam boxes in 2003. Despite my fundamental and unchanged concern about the generation of instant, non-biodegradable waste, with careful handing styrofoam boxes can have a long, productive life.

Jerry, Scott Taylor, Brett Ramsey, & Karen Leng filming self-watering pot - 2
Making a self-watering pot to grow ginger.


That frequently asked question:
Can I grow plants in styrofoam boxes? Someone told me they are toxic…

Over the years I have answered this question, the most common reason for this concern is by someone who is muddling polystyrene up with polyvinyl chloride (PVC) which, depending on the many types commonly used, has been known to release lead, phthalates and/ or dioxin. These are toxins. PVC is used to make water pipes amongst other products, but not for packing boxes.

Other common misconceptions are conflating polystyrene, a polymer, with other plastics that sound similar but are different compounds with different uses, such as styrene, the monomer from which polystyrene is made. They have different properties.

Another misconception about polystyrene arises from the way in which polystyrene food containers may be used, for example polystyrene being used in a microwave to reheat prepared food. Polystyrene vegetable packing boxes are not microwaved.

In short, the polystyrene used to manufacture boxes to cart food are one kind of many kinds of expanded polystyrene. You can’t treat them all equally because they’re not made the same way or for the same purpose.

John & Genny Catlin's shadehouse - 3
Single-use plastic, up-cycled for nursery stock production. Jacobs Well, Queensland.

Re-use, re-purposing and up-cycling polystyrene vegetable packing boxes.

This blog looks at ways to convert expanded polystyrene foam boxes, a single use plastic used for packing vegetables, into a useful gardening asset.

If you endorse the reuse of waste, visit your local fruit shop or supermarket and get some polystyrene vegetable packing boxes. Retailers are happy to sell them for a couple of dollars and you’ll find them suitable for a range of gardening jobs whether your climate is hot, cold, wet or dry.

Polystyrene foam is fragile. When lifting boxes pick them up from underneath instead of just grabbing the corners. This simple difference in the way you handle them can greatly extend their useful life.

native orchids raised in painted styrofoam box.JPG
Native terrestrial orchids raised in a painted polystyrene box.

Polystyrene foam boxes, sold complete with lids, make good storage units for root crops, like potatoes, dahlia tubers or bulbs. Check roots are completely dry, clean and pest free before storing in a cool, dry, well ventilated area like a shed. I sometimes use a hairdryer to make sure they really are dry before storage. A light dusting of powdered sulphur over ornamental bulbs or corms checks mould, pests like wireworm. It also deters vermin.

To make a basic container for growing, cut eight 1cm square holes in the bottom of a polystyrene box to create a freely draining container. Chicory suits this use, the box is helpful for containing this freely suckering vegetable which can become a nuisance weed in a mixed planting.

styrofoam box protects tall cuttings
Using tall sided polystyrene boxes to hold and protect tall cuttings in tubes from wind damage.

Polystyrene foam boxes are ideal containers for growing tubestock, conveniently holding the  contents upright, sheltering small plants from drying winds.

Polystyrene boxes are a form of modular growing. I use them to transport tubestock and small plants. These boxes stack well in a car. They also stack well on a small sack barrow. In a heatwave, I can move box-grown plants, like strawberries, from a sunny location to a shadier one in moments.

$50k worth of Alcantarea seedlings - 3
What does $50,000 look like? asked John Catlin, a plant collector, breeder, nursery grower and enthusiastic conservationist. “Polystyrene boxes provide an ideal substrate for germinating bromeliad seed. You’re looking at potentially $50k’s worth of Alcantarea”.

The bottoms of polystyrene boxes are flat, so if you stand them on an equally flat surface, like a concrete balcony or tiled patio, this can impede drainage. Nurseries stand boxes like these off the ground on wire benches to discourage slugs, snails and root rot diseases that can be spread in stormwater and irrigation runoff, like damping off disease (Pythium spp.). Alternatively stand them on bricks or a porous surface, such as gravel or mulched ground.

Before adding compost or potting mix, first cover each drainage hole with a crock. Do not use pebbles, as these block drainage holes. Crocks are curved pieces of broken terracotta or ceramic pot used to create a ‘bridge’ over the hole. Position one crock over each drainage hole so that the gap created permits water to drain around them whilst supporting the growing medium.

sweetpotato cuttings in styrofoam box - 1
Sweetpotato cuttings taken in winter.

Use boxes for raising seedlings or striking cuttings. Deep boxes afford wind protection, which means young plants stay moist longer, reducing watering. Their depth also makes them suitable for sowing large, slow to germinate seeds, like macadamia and palm seed, in a deep layer of propagating mix.

Cuttings of slow to develop plants, like Polyscias guilfoylei, seem to develop better fibrous root systems in boxes than in seed trays. You’ll use less water rooting them in boxes than outdoors in garden beds or seed trays.

Plants which produce rapidly growing, deeply penetrating ‘dropper’ roots, like Pandanus, may root right through the bottom. Left for too long, potting up Pandanus seedlings may involve destroying the box, which negates the exercise. Check under the boxes for early signs of emerging roots. Better still, stand the boxes on wire mesh nursery benches.

chillies, mexican tarragon, styrofoam box
Chilli, Mexican tarragon seedlings protected from summer heat by polystyrene, which is an excellent insulator.

Polystyrene foam is an excellent insulator, and because they’re normally coloured white, boxes also reflect heat. This means they protect against both winter frost and summer heat. For added sun protection, drape some 50% shadecloth or old net curtains over the box. For added overnight frost protection, use shadecloth or fabric like an old towel or bed sheet.

Boxes make the lightest growing container possible, so they’re ideal for making mini-gardens for rooftop or balcony gardens. A hotel in Sydney grew an all year round supply of strawberries on its rooftop using polystyrene boxes. A deep box filled with a growing medium is deep enough to grow cherry tomato, a dwarf lemon or a cumquat, salad vegetables, herbs, spices, even stump-rooted crops like radish, beetroot, carrot ‘Paris Market’, celeriac and kohl rabi.

I have demonstrated how to use polystyrene boxes to make a cheap worm farm. Why buy one when you can up-cycle?

basic styrofoam worm farm - 3
Polystyrene worm farm.

 

Polystyrene boxes can also be adapted to serve as self-watering containers. I grow my biggest crops of ginger fastest in these self-watering containers and I use less water in the process.

Home gardeners in the wet tropics report that growing vegetables in these boxes is one way of ensuring continuous summer production when vegetables growing in waterlogged garden beds are rotting.

ginger, Zingiber officinale/ self-watering pot - 1
Ginger thrives in a polystyrene self-watering pot. These containers are readily transportable too.

I find that using them for propagation is one of the best ways to conserve water and to protect plants from damaging, desiccating winds.

Polystyrene, a bigger picture

If you want to avoid the generation of polystyrene waste, it is difficult. Polystyrene is one of the most widely used plastics in manufacturing goods.

Polystyrene foam is used to protect products sold in cartons. It’s used for insulation in buildings and white goods, for disposable cutlery and cups (like instant noodles), for cartons, and for shock absorbing padding used in the transportation of fragile products, from computers to televisions.

The International Pollutants Elimination Network’s Ocean Pollutants Guide reports (go to Page 51):

Unreacted monomers in plastics and resins, as well as degradation products, can leach from the [plastic] polymers into the environment, eg, chemical intermediates from the partial degradation of polystyrene“.

This is true. Several million tonnes of polystyrene are made each year. There are different methods of manufacture and the products are used for different purposes. Unfortunately you cannot compare a polystyrene insulation with a polystyrene knife or fork and treat them as chemical equals in the waste stream or in the environment. It’s complicated.

Styrene by-products have been shown to migrate from polystyrene products, e.g., from instant noodle polystyrene cups. Styrene is an animal carcinogen, a possible human carcinogen and a neurotoxin“.

This is also true. Only this does not relate to all kinds of polystyrene; polystyrene packing boxes are definitely not microwavable and, because of their size, they are not exposed to microwaves in microwave cookery.

EPS may also contain the [Persistent Organic Pollutants] POPs flame retardant HBDC (or HBCDD). Elevated HBCD levels were found in oysters from aquaculture farms where EPS/XPS buoys containing HBCD were used. High levels of HBCDD have been found in fish in some European waters“.

Again, true. However, polystyrene vegetable packing boxes do not contain flame retardant chemicals because they are used for cartage, not insulation.

Polystyrene is combustible and it produces thick, black smoke. So when your vegetable packing box reaches the end of its useful life in the garden, bin but do not burn it. Since polystyrene vegetable packing boxes are flammable like cardboard, they should be stored accordingly.

Can polystyrene be recycled?

Yes, polystyrene can be recycled. One industrial process is pyrolysis. Pyrolysis is more expensive than the value of the recycled plastic, so it doesn’t happen.

Can polystyrene be biodegraded?

Yes, polystyrene can be biodegraded. Certain organisms have demonstrated they can feed on it, including the larvae of two species of darkling beetle. One is familiar – the mealworm (Tenebrio molitor) is the larva of a species of darkling beetle. The larvae of another darkling beetle species (Zophobas morio) is also used to biodegrade polystyrene. The soil bacterium Pseudomonas putidathe world’s first patented organism, can also digest polystyrene. I have posted about these on my public Facebook page.

Potential health risks of all forms of polystyrene

From 1999 to 2002, a comprehensive review of the potential health risks associated with exposure to styrene was conducted by a 12-member international expert panel selected by the Harvard Center for Risk Assessment. The scientists had expertise in toxicology, epidemiology, medicine, risk analysis, pharmacokinetics, and exposure assessment.

The Harvard study reported that styrene is naturally present in trace quantities in foods such as strawberries, beef, and spices, and is naturally produced in the processing of foods such as wine and cheese.

The study also reviewed all the published data on the quantity of styrene contributing to the diet due to migration of food packaging and disposable food contact articles, and concluded that risk to the general public from exposure to styrene from foods or food-contact applications (such as polystyrene packaging and food service containers) was at levels too low to produce adverse effects”.

John & Genny Catlin's shadehouse - 5
Single-use plastic, up-cycled for nursery stock production. Jacobs Well, Queensland.


Polystyrene in the garden

Horticulture contributes to polystyrene filling up landfill and polluting waterways. In its granular form, expanded polystyrene foam is used in orchid and saintpaulia potting mixes by growers who do not care that it lacks any benefits to the plants they retail.

Perlite, vermiculite, charcoal (including biochar) are also lightweight products used in growing media, but the purpose for the use of each in horticulture is they benefit the plants being grown. They cost more than expanded polystyrene and they are not added simply as cheap fillers to save money in mass production.

Polystyrene is very cheap and therefore increases profits for greedy growers. I refuse to buy plants grown in potting mix containing expanded polystyrene – these people are not interested in plants, just profit.

I started using polystyrene foam boxes in 2003, and they’re still handy and working. Despite my concerns about the generation of this instant, non-biodegradable waste, with careful handing they can have a long, productive life, wherever you garden.

If you endorse the reuse of waste, visit your local fruit shop and get some polystyrene vegetable packing boxes. Retailers are happy to sell them for a couple of dollars and you’ll find them suitable for a range of gardening jobs whether your climate is hot, cold, wet or dry.

Final word on styrofoam vegetable packing boxes

Avoiding over consumption is important. In this instance, the re-use, re-purposing or up-cycling of styrofoam vegetable packing boxes means you can avoid buying containers for plants, plant propagators, seed boxes, worm farms, etc.

The phrase it’s not about earning more money, but spending less can be applied here. Reduced consumption reduces your ecological footprint by reducing the consumption of finite resources. In doing that you also reduce greenhouse emissions generated during production. In the lifetime of many manufactured products, from cars to self-watering pots, it is the manufacturing process and getting that product to your home that generates more greenhouse gases than are generated during its operational life.

If re-using polystyrene boxes means deferring the unnecessary consumption of specially made gardening products – even for a few years – this gain outweighs sending them from the supermarket to the landfill the moment their contents reach the shelves.

A little joined up thinking.

I’ll let Polystyrene of X-Ray Spex sing you out with ‘The Day the World Turned Day-Glo’ (1978).

Jerry Coleby-Williams

1st October 2008

4 Comments Add yours

  1. Kristina Andrew says:

    Thank you for this article, I have been using these polystyrene boxes, but kept getting conflicting information on its uses and whether it was safe to use.
    I don’t want to buy pots, and they are the perfect solution.
    I will definitely be checking potting mix now, I didn’t know they put rubbish like that in them!
    I really thought the standards were better than that.
    Thank you Kristina

  2. linnie says:

    Thank you, Jerry 🙂 I read this with interest as I have been using these boxes for over a decade, closer to two, but I’ve been using them for slow germinating rainforest tree seeds etc, and cuttings of non-edible species garden plants. I’ve been placing much more emphasis on edible and medicinal plants now, so what I propagate needs to be non-toxic… I’m absolutely delighted to know that these polysterene boxes are safe, as I have a shadehouse full of them, but now need more as I will try the ginger in them this year. Another wonderfully informative post. Thank you 🌱🌻🎋🍀🌾🍄🌼🌹🌿

  3. Doug Van Wyk Smith says:

    Really enjoy your down to earth articles, gardening life experiences, priceless support for sustainability, responsibility. Thank You Jerry.

  4. Brenda says:

    Great info. Have shared with my gardening group. Many thanks.

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