Is It Safe to Grow Vegetables In Polystyrene Boxes?

If you’re trying to grow vegetables, you may wonder if growing them in polystyrene boxes is ok.

Polystyrene can be helpful for many things, and polystyrene boxes should be ok to use to grow vegetables as long as you take some precautions. 

Polystyrene waste in a garden

Does polystyrene leach into soil?

In general, the levels of polystyrene in containers are not high enough to cause any problems. Generally speaking, growing plants in recycled foam planters is safe. 

However, if you’re worried about the potential effects of growing edibles in styrofoam, don’t grow them. Once you’ve used your food planter, recycle it. Do not burn it – this may release toxic substances.  

Is it safe to grow food in polystyrene? 

Yes, you can use polystyrene boxes to grow food. Many people confuse polystyrene with PVC, polyvinyl chloride, which can release the toxic substances dioxin, lead, and phthalates. Water pipes are made out of PVC but not packing boxes. 

People also often confuse polystyrene, a polymer, with other plastics that sound similar but are different compounds with different purposes. Polystyrene, for example, is derived from styrene, but they behave differently. 

The other misconception about polystyrene comes from its use in food containers, such as microwaveable polystyrene containers. Polystyrene vegetable packaging boxes cannot be microwaved. 

Can I use polystyrene in plant pots? 

Styrofoam can degrade in plant pots, leaving you with sunken containers. However, you can test your styrofoam to see if it breaks down.

Just soak some of your packing peanuts or broken bits of Styrofoam in water for several days. Do not use the pieces in pots if they start to dissolve. 

Growing vegetables in styrofoam boxes 

Make a simple growing container by cutting eight 1 cm square holes in the bottom of a polystyrene box. Chicory is a perfect plant to use because it can become a nuisance weed in a mixed planting. 

Polystyrene boxes are ideal for growing tube stock like potatoes, sweet potatoes, and yams. Their upright design protects them from drying winds. 

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You can use them for modular gardening. They can be used to transport tube stock and smaller plants. They stack easily in a vehicle and fit in a small sack barrow. Strawberries, for example, can be moved from a sunny to a shady location within minutes in a heatwave. 

If you place polystyrene boxes on a flat surface, such as a concrete balcony or tiled patio, the bottoms become clogged with water. 

Nurseries place boxes like this on wire benches to discourage slugs, snails, and diseases spread by rainwater and irrigation runoff, like damping off. Alternatively, stand them on gravel, mulched ground, or bricks.

Cover each drainage hole with a crock before adding compost or potting mix. Avoid using pebbles, as they can block drainage. Crocks are broken pieces of terracotta or ceramic pot used to create a “bridge” over the hole.

Cover each drainage hole with a crock to create a gap that allows water to drain while supporting the medium. 

How to grow plants in styrofoam containers 

What you’ll need:

  • Foam box
  • Trowel
  • Potting mix
  • Compost or aged cow manure
  • Blocks
  • Sprouts
  • A tonic made of seaweed
  • Mulch
  • Water
  • Cloth for shading
  1. On each side of the box, drill six drainage holes.
  2. Fill the box with a good potting mix. Add aged cow manure or composted homemade or bought compost to the potting mix. Manure or compost helps the mix hold water and nourish the vegetables. Compost or manure should account for 10-30 percent of the mix. 
  3. Raise the box by placing bricks on top to facilitate drainage. Choose a location for the veggie boxes in the sun or in the shade in the afternoons. Now you can plant the seeds. 
  4. Use advanced lettuce or other seedlings for fast results. You may want to plant just a few seeds at a time if you can wait a little longer and want to save money. So that you can gradually plant the remaining seeds, seal the seed packet and keep it in a cool, dry place.
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It’s important not to overplant. Please keep it to four lettuce plants, one or two herbs, and one tall tomato or cucumber plant per container. If you want more crops, plant more boxes slowly to have some crops coming on. 

Spread pea straw, sugar cane, or lucerne mulch around new plants after watering them with a seaweed plant tonic. Doing this helps the roots stay cool and moist. Apply the mulch loosely so that water can still penetrate. 

How to make styrofoam planters  

Ingredients needed:

  • Cement
  • Large and old tub, bucket, or bowl
  • Some styrofoam pieces
  • Water to mix
  • Latex gloves
  • Waste plastic sheet
  • Sieve with a 3 mm opening
  • Any scale or ruler
  1. Put cement in a large bowl. Grate the styrofoam pieces on it using a sieve. 
  2. Mix the cement and foam pieces with water. Be sure to wear latex gloves while doing this. The water to cement/styrofoam ratio must be 1:4. Mix the water into the concrete slowly and gently to be well blended. It should not be runny.
  3. Put a plastic sheet on a flat surface. As you flatten the cement/styrofoam mixture by hand, slowly start forming the planter’s base. Try to smooth it out. You can make any shape you want because you’ll even it out later. 
  4. Mark the dimensions on the cement surface with a ruler or scale. After marking them, carefully remove excess cement from the sides. Smooth the concrete edge with a knife. 
  5. Create small oval shapes from the concrete mix and place them on the edge of all four sides, using very little concrete. You can do this on any side you choose. There can be no space left after stacking these shapes, so you should be very careful. Make sure all shapes adjacent to each other stick together or are connected. 
  6. Make two stacks with the same oval shapes and partition the center of the square base if you want to grow two plants in the same pot. 
  7. Continue stacking one by one. Make the second divided planter three steps taller; if you do, there should be a good height difference between the two. 
  8. Create a drainage hole so the roots can breathe. It takes 24-36 hours for the planter to dry completely. Keep it in the shade and out of the sun. 
  9. Use a spray bottle to spray water on all sides of the planter once it has completely dried. Water is the best and oldest way to cure concrete. Hydration occurs when the concrete hardens. Keep the new concrete moist for at least three days while it cures. This will make the concrete strong. 
  10. Take off the plastic sheet after the concrete sets. It will come out right away. The best thing is that you don’t have to smooth the edges because the planter’s rough texture comes from styrofoam. 
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Now you can pour some soil into the planter and plant flowers of your choice. 

Polystyrene FAQ

Is polystyrene poisonous to plants? 

In general, no. Polystyrene levels in products are not high enough to lead to contamination. 

Is styrofoam safe for vegetable gardens? 

No. It can be harmful to add styrofoam peanuts to a pot without drainage. Roots that grow deep into foam material can become waterlogged, rot, and die without enough drainage. 

What are the safest containers to grow vegetables? 

When it comes to growing vegetables, there are several options. These include:

  • Containers made of natural stone and concrete
  • Recycled plastics
  • Wooden containers