styrofoam peanuts for drainage

dlg421March 24, 2011

In reading some past threads on this site I see that there are negative feelings about using styrofoam peanuts in the bottom of containers to allow adequate drainage. I have always used gravel in the bottoms, but using gravel makes the containers heavy. So this past winter (I am AZ so we plant things in the winter here) I planted several containers with geraniums using the peanuts at the bottom. The containers with the peanuts are lighter to move around and I can see no difference in the health or performance of the plants in those containers vs. the ones with gravel.

I would appreciate and specifics as to why the use of the non-biodegradeable peanuts is not a good idea.


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tapla (mid-MI z5b-6a)

If you want to deal with what you're left with after you've finished with your soil/peanut blend, then they work fine to reduce the volume of soil it takes to fill the container and to lighten the container. The main point is they do nothing to improve drainage or aeration, and they simply shift the PWT to a higher point in the container; so to that end they are counterproductive. I also think that empty soda cans or milk jugs with screw on lids work much better and provide a cleaner method o/a, of providing filler to accomplish the same goal you mentioned; plus they can actually add some drainage benefits in certain cases because of how they alter the way water is held.


    Bookmark   March 24, 2011 at 4:28PM
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rhizo_1 (North AL) zone 7

If you wish to use the peanuts, you can use some sort of mesh bags or even panty hose to confine them. Those old fashioned mesh grocery bags are terrific. The primary draw-back many people have with the peanuts is how messy they are when you need to repot or change out your plants. I've used the PP for many years in my large annual container plantings with no problems (now that I use mesh bags).

If you do end up using the PP, you'll be amazed at how much the roots of your plants love growing amongst them. At the end of a growing season, when I am pulling up the plants to toss, the PP always come up, too. The root system grows down and around and in and out of those things, using them as a growing medium.

If you enclose the peanuts, you can surgically remove the bags from the roots, and reuse them.

    Bookmark   March 24, 2011 at 5:02PM
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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.

Here is a link that might be useful: Container Soils - Water Movement & Retention 13

    Bookmark   March 24, 2011 at 7:44PM
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greenman28 NorCal 7b/8a

Ditto what Jodi wrote!

Disparate layers don't increase drainage properties.


    Bookmark   March 24, 2011 at 8:03PM
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edweather(Zone 5a/b Central NY)

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.

    Bookmark   March 24, 2011 at 9:32PM
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tapla (mid-MI z5b-6a)

Expanded polystyrene styrofoam (EPS)


    Bookmark   March 24, 2011 at 11:34PM
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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!


    Bookmark   March 25, 2011 at 12:39AM
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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

    Bookmark   March 25, 2011 at 10:56AM
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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.



    Bookmark   March 25, 2011 at 11:51AM
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greenman28 NorCal 7b/8a

Dlg, don't feel bad!

I labored under the same misconception for years!


    Bookmark   March 25, 2011 at 12:10PM
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donaldb(5B Worcester, MA)

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

    Bookmark   March 26, 2011 at 9:17AM
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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.


    Bookmark   March 26, 2011 at 11:17PM
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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.

Happy Gardening!

    Bookmark   March 27, 2011 at 9:59AM
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tapla (mid-MI z5b-6a)

I agree that you shouldn't feel at all bad, or that you did something wrong. A large part of the gardening community still clings to the belief that drainage layers improve drainage. We know, of course, that they do no such thing. Also, if you're tempted to use peanuts or gravel in the bottom of your pot to take up space, you might wish to consider this: As Jodi mentioned, empty soda bottles or other plastic or glass containers with screw-on lids do a superior job - much neater. Also, they allow soil continuity that bridges the PWT and the pot bottom. This means that the entire PWT of heavy soils is likely to be contained within the small fraction of soil that surrounds these large fillers. If you use peanuts as the filler material, water either perches above them (if you use something to separate the peanuts from the soil, like screening); or if you incorporate them, you simply have less soil for roots to colonize - exactly what the empty soda bottles accomplish w/o the mess. Peanuts are closed-cell foam, so roots can find their way into small surface irregularities,. but they cannot penetrate the foam. This has the effect of simply reducing the amount of soil that is available for root colonization.

Finally, if all you need is extra ballast for weight/stability, simply fill the jugs with water and voila! - instant ballast w/o the fuss & muss of gravel. This method also reduces the volume of soil that CAN support perched water - thereby reducing the total volume of perched water in a container, unlike gravel layers which simply raise the ht of the PWT in the container.

If you aren't after the extra weight, overturning a cone-shaped container that fits fairly snugly in the bottom of the planting container is the best way to take up space - plastic, if you want to save on weight. It neatly and effectively displaces most of the soil that would normally hold perched water, using a little science to improve conditions, and what's lighter than the air .

I'm not going to suggest or debate how precise your growing efforts should or shouldn't be, DLG, that's for you alone to decide; but I will say that simply putting things you've learned to work FOR you, especially when they require no or little additional effort, can only improve your growing experience.

Take care.


    Bookmark   March 27, 2011 at 3:08PM
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Again thanks to all for your responses. I have learned a lot from your answers.

Best regards.


    Bookmark   March 28, 2011 at 2:02PM
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I got the biodegradable peanuts by mistake last year, and did they ever biodegrade! Within an hour of planting and watering, the level of the potting soil sank by 1/3! Never again!

    Bookmark   May 16, 2012 at 1:27PM
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