Using Styrofoam In Containers – Does Styrofoam Help With Drainage

Using Styrofoam In Containers – Does Styrofoam Help With Drainage

By: Darcy Larum, Landscape Designer

Whether set on a patio, porch, in the garden, or on each side of an entryway, stunning container designs make a statement. Containers are available in a wide array of colors shapes and sizes. Large urns and tall decorative glazed pots are especially popular these days. While decorative pots like this add to the beautiful dramatic appearance of container gardens, they have some drawbacks.

When filled with potting medium, large pots can be extremely heavy and unmovable. Many glazed decorative pots may also lack proper drainage holes or do not drain well due to all the potting mix. Not to mention, purchasing enough potting soil to fill large pots can become quite expensive. So what’s a gardener to do? Read on to learn more about using Styrofoam for container filler.

Using Styrofoam in Containers

In the past, it was recommended that broken pieces of clay pots, rocks, wood chips or Styrofoam packing peanuts be placed in the bottom of pots as filler and to improve drainage. However, research has shown that clay pots, rocks and wood chips may actually cause the pots to drain slower. They can also add weight to the container. Styrofoam is lightweight but does Styrofoam help with drainage?

For decades, container gardeners have used Styrofoam for drainage. It was long lasting, improved drainage, did not add weight to the pot and made an effective filler for deep pots. However, because landfills are overfilled with non-biodegradable products, many Styrofoam packing products are now made to dissolve in time. It is not recommended to use Styrofoam peanuts for potted plants now, because they may break down in water and soil, leaving you with sunken in containers.

If you find yourself with a large amount of Styrofoam from product packing and question: “Should I line potted plants with Styrofoam,” there is a way to test the Styrofoam. Soaking these packing peanuts or broken bits of Styrofoam in a tub of water for several days can help you determine if the type you have breaks down or not. If pieces begin to dissolve in the water, do not use them in the bottom of pots.

Does Styrofoam Help With Drainage?

Another problem gardeners have had when using Styrofoam in containers is that deep plant roots may grow down into the Styrofoam. In pots with little to no drainage, the area of Styrofoam may be waterlogged and cause these plant roots to rot or die.

Styrofoam also contains no nutrients for plant roots to absorb. Too much water and lack of nutrients can cause beautiful container designs to suddenly wilt and die.

It is actually recommended that large containers be planted in the “container in a container” method, where an inexpensive plastic pot is planted with the plants, then set atop filler (like Styrofoam) in the large decorative container. With this method, container designs can easily be changed out each season, plant roots are contained within the potting mix and, if Styrofoam filler does break down in time, it can be easily fixed.

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Q: Are you supposed to put gravel or clay shards in the bottom of containers to improve drainage?


One of the most important aspects to consider when deciding how to insulate plants is their location. Plants located on the ground will receive some of their needed heat from the ground itself. This particular location allows for using mulch, leaves, dirt or simply tossing a blanket over the entire plant, including the pot. However, plants on a plant stand or on a deck need to be covered entirely, even the bottom. Otherwise, the cold air will enter the plant from the bottom of the pot and damage the potted plant.

  • Potted plants are an attractive addition to any home or apartment.
  • This particular location allows for using mulch, leaves, dirt or simply tossing a blanket over the entire plant, including the pot.

Good basic tips and a timely reminder for new gardeners bit by the gardening bug and spring fever!

Terry thanks for letting us know that the container article was useful for you. Enjoy & keep having fun in the garden!

If you are reusing containers from previous years do you empty and use detergent to clean them out before filling with soil again?

There are many recommendations on sterilizing pots for re-use. That being said, I’ve worked in propagation greenhouses that don’t bother. As for using detergent, we’ve never seen a soap product suggested as such.

Should the pot have a hole in the bottom for drainage?

Susan, Yes. Planted pots should always drain.

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For many years I used a gravel layer in the bottom of my containers, thinking I was doing a good thing, providing a "layer of better drainage" for my plants. In reality, though, those different layers don't work as we might think within a pot, and are actually detrimental.

Once I learned how water moves through soils, and what causes perched water to remain inside pots of soil, it became clear that it's much better to have one single layer of medium from top to bottom within a container.

The article contained within the link below explains how water moves through soils, what a perched water table is, what good drainage means and how to achieve it, and explains moisture retention. It also explains the basics of what plants and their roots require within the confines of pots, and the relationship between roots, soils, water, and plant nutrition.

It's a valuable article for us dedicated container growers, and it puts to rest a few old wive's tales that continue to circulate throughout the gardening world!

It boils down to simple science, simple physics. the reaction of liquids and solids when mixed. Since growing in the ground is so very different than growing in containers, we have to adapt certain ideas to fit. The article I've linked is very eye-opening, very logical, and I'll never again place a layer of anything under the medium I use. I let the properties of my medium do the work of proper drainage.

Greenman28 NorCal 7b/8a

Disparate layers don't increase drainage properties.

Edweather USDA 9a, HZ 9, Sunset 28

This is probably a digression off thread, but maybe a good place to interject a funny thought I had yesterday. I received a 2 cu ft bag of perlite in the mail. It came packaged in a thin plastic bag. My immediate thought was that this seemed familiar to me. BEAN BAG CHAIR!! So what is in those Bean Bag Chairs anyway? I doubt it's perlite. I don't think it's a good idea to slit mine open and find out, but I did think that whatever is in them would possibly be a good soil amendment too.


Expanded polystyrene styrofoam (EPS)


I agree with rhizo, peanuts work great. Orchid roots love them as do dirt plants. I always save them and fill my big, outdoor containers with them. Roots love them!

Calistoga_al ca 15 usda 9

I only used them once, preparing a cane wash basket as a gift of assorted herbs to a relative. I covered the peanuts with landscape fabric and potting soil on top to plant herbs in. It worked fine for growing the herbs and drained well. The real problem was it was really unstable, prone to being top heavy and falling over and dumping soil and plants onto the floor. Al


Thanks all for your thoughtful responses.

Using gravel in the bottom of containers was taught to me by my grandmother. All these years of doing it for nothing! Oh well, I am glad that I found this forum and gained some new insights.

Greenman28 NorCal 7b/8a

I labored under the same misconception for years!


I've been using them for years. Orchids love them and all my larger outdoor container plants have had them for over 6 years.


Dig, don't feel you were doing something wrong. I frequently use gravel for weight on top-heavy plants. Some plants need bottom weight to keep from falling over.

Growing should not be so precise. There's plenty of room for creativity and should not be seen as negative. Use gravel, peanuts, cans and bottles. I use them all. really doesn't matter.


It's a myth, a fallacy, an old wive's tale that has circulated the gardening world for decades. eons, even! Why? I couldn't say. My Grandmother did the same thing, placing a layer of gravel inside a pot with soil over it. though I'd bet she couldn't tell you why, or how she thought it worked.

There's no reason to feel bad. we've all been there! It's part of the learning process, I think, but what separates good growers from great growers! I used to do it, too, though I have no idea why I followed the crowd and didn't do my homework. I've found it best to step away from that crowd, and to actually learn why and how things work. Learning the basic science behind what we do as gardeners can, and has, put me ahead of that crowd.

The truth is, layering medium materials of differing size within the confines of a pot does, indeed, cause a perched water table to sit right above the spot where those layers meet. It's simple physics. basic science that we all learned back in school. It's just how water and certain solids react when gravity happens!

There are other, much better methods for gaining the drainage we need. The best way to acquire that drainage is to begin with a medium that allows for excellent drainage by virtue of its very properties. Utilizing a medium of larger particulate will solve this, and several other issues encountered when growing within pots. such as maintaining aeration, which allows for a good exchange of oxygen and gases to and from the root zone. very important for sustained root health.

One of the first things to learn is that there are vast differences between growing in the ground, and growing within the confines of containers. It's also very helpful to know the function of a medium. The link I provided above, in my other post, contains that information.

There are also other ways to compensate for excess weight within large pots. Placing empty milk jugs or soda bottles within the container can take up some of the space used by soil, thereby making the container lighter by volume, but still eliminating that perched water table we need to avoid. Al mentions this in his post above.

The reason I went looking for more information on soils and water retention in the first place is that several of my plants and potted bulbs were displaying signs of severe root rot and other issues. Once I found the information and learned how water and soil behave together within a pot, I un-potted one of my bulbs to have a closer look. Sure enough. right there, above the gravel layer, at the very bottom of the soil layer, the roots were dead and decayed. and though the top layers of soil were dry, the bottom layers were still wet, and discolored by obvious over-saturation.

The bottom line is this. everyone will make their own choices regarding how much they learn, how much effort they want to give to growing their plants, and by what methods they grow. But the facts are the facts, and knowledge does truly bring us success. It's always a good thing to have accurate information from which to draw, so we can make informed choices.

I suspect many of the gardening fallacies and old wive's tales will continue to circulate, perpetuated by folks who have no thought of expanding their knowledge or improving their gardening efforts. For myself, however, it makes more sense to delve a little deeper, winnowing the chaff from the grain, so to speak. I will be better prepared to make informed choices in my growing, and I'll certainty reap the rewards of those efforts.

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