Is it OK to put styrofoam in the bottom of a planter?

Using styrofoam in the bottom of plant pots and planters is a common practice for both home gardeners and commercial plant growers. Styrofoam, also known as expanded polystyrene (EPS), can provide some benefits as well as some potential drawbacks when used in this way. Let’s take a closer look at the pros and cons of using styrofoam in planters.

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Pros of Using Styrofoam in Planters

There are a few reasons why someone may choose to put styrofoam in the bottom of their plant pots or planters:

It lightens the overall weight of the planter – Styrofoam is extremely lightweight, so adding a layer of it to the bottom of a planter can make it easier to move the planter around.
It takes up space – Styrofoam can help take up volume at the bottom of a pot or planter so less potting mix is required to fill it.
It improves drainage – The gaps and air spaces in styrofoam allow excess water to drain out of the soil more quickly and prevent water-logging.

It provides insulation – Styrofoam acts as an insulator, which can help buffer plant roots against temperature extremes in very cold or very hot weather.
It’s inexpensive – Styrofoam is an affordable, accessible material for many gardeners.

For these reasons, adding a layer of styrofoam pellets, pieces, or sheets to the bottom of pots and planters is a strategy used by many gardeners and nurseries.

Cons of Using Styrofoam in Planters

However, there are also some potential downsides to be aware of when using styrofoam in planters:

It’s difficult to re-use – Unlike materials like gravel or clay pot shards, styrofoam does not break down and can’t be composted, so it’s hard to reuse year after year.
It’s a contaminant – Little bits and dust from styrofoam can make their way into the soil and cause issues, and if pots crack or break, it also contaminates the surrounding environment.

It harbors pests – The nooks and crannies of styrofoam sheets or pellets provides places for slugs and other pests to hide.
It contains toxic chemicals – Polystyrene contains the toxic chemical styrene, which can leach into soil and water supplies.
It’s difficult to transplant from – The roots of plants can become very embedded in styrofoam, making it hard to transplant them without damage.

These potential problems have led some gardeners and nurseries to move away from using styrofoam in planters and seek out more sustainable options.

Alternatives to Styrofoam

If you want to avoid the drawbacks of styrofoam but still need lightweight, space-filling drainage material for the bottom of your planters, there are a few good alternatives to consider:

Perlite – Made from volcanic glass, perlite is an extremely lightweight soil amendment that improves drainage.

Vermiculite – This is a natural mineral product that expands when heated, creating many air pockets that retain water while still permitting excess drainage.
Pumice – Crushed pumice rock provides a nice weight while still promoting air circulation and drainage in the soil.
Coarse sand or fine gravel – Inexpensive options that offer weight and drainage.

Shredded wood, bark, or coconut coir – These natural materials provide drainage and aeration as they decompose.
Clay pot shards – Broken pieces of old clay pots are perhaps the most sustainable option, as they will not decompose into the soil over time.

Switching to materials like perlite, vermiculite, bark, or gravel may involve a somewhat higher upfront cost than styrofoam. However, these materials are reusable year after year and avoid the problems associated with contaminated styrofoam accumulating in local landfills. For many gardeners, the switch is well worth it!

Best Practices for Using Alternatives

When selecting and using alternate materials in place of styrofoam, keep these tips in mind:

Pick an option suitable for the types of plants you’ll be growing. For example, cacti and succulents would appreciate extra drainage from materials like perlite or pumice.
Aim for approximately 2-3 inches of material at the bottom of containers. This provides drainage while still leaving plenty of room for potting soil.

Rinse materials like perlite or vermiculite before use to remove any dust or debris.
Re-use materials year after year as you re-plant containers.
Watch for issues like soil fungus gnats if woody amendments like bark start decomposing.

Avoid potential problems like soil compaction by never using rocks or gravel that are too large in size.

Conclusion

While styrofoam has been a popular choice for the bottoms of planters in the past, environmentally conscious gardeners may want to consider alternative options. Materials like perlite, vermiculite, pumice and gravel offer excellent drainage and weight, without the drawbacks of contaminated styrofoam waste. With some planning and forethought, sustainable materials can be used in planters instead of styrofoam for many seasons to come.

Material	Pros	Cons
Styrofoam	Lightweight Takes up space Improves drainage Provides insulation Inexpensive	Not reusable Can contaminate soil Harbors pests Contains toxic chemicals Roots become embedded
Perlite	Extremely lightweight Improves drainage Reusable	More expensive than styrofoam
Vermiculite	Lightweight Retains moisture Allows excess drainage Reusable	More expensive than styrofoam
Pumice	Provides weight Promotes drainage Reusable	Heavier than styrofoam
Sand/Gravel	Inexpensive Provides weight and drainage Reusable	Heavier than styrofoam Can compress roots if too compacted
Bark/Coir	Natural materials Improve drainage Reusable	Can decompose into soil May harbor fungus gnats
Clay Pot Shards	Sustainable Will not break down in soil Reusable	Can harbor sharp edges