miss_moose

Using Sodium Polyacrylate in the Garden?

If you don't know what SP is, it's a polymer that is super absorbent and found in disposable diapers. It can hold many times its weight in water and seems like a good idea for stretching between waterings as my garden gets full sun in the mid summer and we go away on weekends a bit. I have a 4 year-old and some unused diapers from when she was smaller stashed away. Can I take out the crystals and mix it with a medium and use it for plants... more specifically, plants I'll be eating such as herbs or potted peppers, etc? Has anyone ever tried this? I know they sell absorbent gel at the garden centre... anyone with experience with this would be greatly appreciated!

Comments (24)

  • daninthedirt (USDA 8a, HZ10, Cent TX, Sunset z30)

    It's approved by the DoA for agricultural use. It's very benign, according to its MSDS. It's not going to hurt you if you eat it. I think garden centers used to sell it -- wasn't it called "ASAP"?

    The only red flag I can come up with (aside from the fact that it displaces nutrients) is that it expands dramatically when it soaks up water. I mean a LOT. I'm not sure what that might do to roots embedded in the stuff. But maybe if it's just mixed with soil, it might not harm the roots.

    That being said, it's not good to get a lot of it on you. It sucks up all bodily fluids, and drys the skin a lot. One might wonder whether, when it dries out, it would do the same thing to plant roots. That is, it'll pull the water out of plants.



  • balloonflower

    Having cleaned up the stuff when a diaper exploded, I'm not sure how it rehydrates once dried out. It's also not really designed to release it's moisture, but keep it in. But I've never tried it. I think it really calls for an experiment. Or, just donate the diapers to a shelter that would use them.

    On a side note, most herbs need very well draining soil, especially in containers, so I specifically make sure my potting soils don't contain any sort of water retention feature. Especially the Mediterranean bunch--rosemary, sage, thyme, oregano, lavender...

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  • Miss_Moose (Winnipeg, Canda. Zone 2)

    Thanks everyone. I was thinking of adding the absorbed crystals to a potting soil mixed with possibly some kind of rock/gravel medium to increase circulation and drainage. Maybe like a 1 part absorbed crystal, 2-3 part soil mixture. I guess my main concerns would be,

    1. Would it cause rot/ fungus under the soil? I'd never have the guts to put it in the garden (mostly because it's not natural) because I'd like to control the water retention to a point, and if it rained or anything... I mean you could never keep track.

    2. Is it biodegradable... where would you dump it in the spring if you needed less water retention, you surely couldn't bury it, you'd have to throw it away.

    3. Apparently it's very dangerous around the eye/ nose-throat area is crystalline form. If inhaled or otherwise, the crystal could get behind the eye or in the lung and then expand. I've had a diaper get destroyed in the washing machine by accident, the crystals are very tacky and hard to manage, so no kids fun planting projects with the stuff I guess. Funny how something so dangerous could be put in a diaper... why not just make it in a more "pad form" rather than free crystals for contact with babies? just a thought

    4. It does retain water, but then releases it so it may be good for like bamboo displays, etc?

    5. Could you start seedlings in it?

    6. Would the crystals retain plant food like they would retain water? I wouldn't want to over-feed my plants because a chemical relationship between feed and SP caused certain elements of plant food to not dissolve/ wash out with waterings and time.

    I'm not posting these to get answers, just to stir thought. I'm really into DIY stuff that can hack high-priced garden products like garden gel they sell for a fortune at the garden centre. It might also be interesting to think of other fun things you can do, like adding food colouring to the gel and creating displays, or colouring your plants as they absorb the colour, or adding plant food to the gel and seeing if it helps keep plants healthier and well-fed (say if you have to go on vacation or just don't have the time). Growing plants in desert areas with the stuff might be successful...


    just a few thoughts


  • daninthedirt (USDA 8a, HZ10, Cent TX, Sunset z30)

    As to biodegradability, no, not really. The stuff will eventually break down, but nowhere near as fast as an organic. Think ground up plastic. Now, you might wonder why such diapers are even allowed in landfills. The answer is simple. Landfills aren't set up for biodegradability. There is no aeration, so a landfill is just a dump. Fill it up and walk away. Even biodegradable stuff that goes to a landfill probably won't biodegrade for a very long time. Of course that means that if you dig this stuff into a garden bed, you're never going to get it out.

    The fact that the stuff is used in agriculture suggests that it might be useful for gardening, but I have never seen a real how-to on it. You might try an experiment with a control -- that is, a pot with some acrylate, and a pot without, and compare growth.

    I remain a little concerned that water is being retained by the sodium acrylate but it's hardly obvious that, so retained, it's giving it up to plants that need it. You can bury bottles of water with your plants, and it won't do them any good.


  • caranee

    Instead of dismantling the diapers, I would use them at the bottom of your pots, particularly hanging pots. I suppose you could also use them at the bottom of your planting holes. They absorb water and release it gradually to the earth, and the plastic covering keeps the water from draining out.


  • digdirt2

    <You might try an experiment with a control -- that is, a pot with some acrylate, and a pot without, and compare growth.>

    Agree that a controlled, and limited, experiment would be best to do first. Too many times what sounds good to us in theory turns out to be a disaster in actual practice. And the more out-of-the-box it is the greater the disaster.

    I see some real potential for both root rot due to poor drainage and extensive nutrient binding and any benefits derived do not appear to off-set those negative issues even in the crystals made for this purpose. So you might want to limit the possible negative side-effects by limiting the size of the experiment and the amounts used. :)


    Related articles and studies

    Dave

  • daninthedirt (USDA 8a, HZ10, Cent TX, Sunset z30)

    "They absorb water and release it gradually to the earth"

    I wouldn't be so sure about gradually releasing much water to the earth. Diapers don't "gradually release" much liquid. You can dry sodium acrylate, with applied heat. I suspect the water that it releases will be just water evaporated from it, and that's not a lot of water at any one time. I doubt very much that it's going to be shedding droplets, for example. I think one picture to keep in mind is that this stuff might just dry out the earth that it's mixed in with, rather than keep it wet. Remember, the point of it in diapers is to suck water away from whatever it touches.

  • carolb_w_fl_coastal_9b

    I imagine it degrades rather quickly, depending on how much salt is in your soil. I've seen a science demonstration showing how salt will cause it to 'melt' away.

  • daninthedirt (USDA 8a, HZ10, Cent TX, Sunset z30)

    I'm not sure why salt would make a difference, and I can't imagine that any functional garden bed would have a lot of salt in it. There are soil microbes that can digest the stuff, but only after it has been exposed to sunlight for a while. I think the sunlight breaks up the large molecules into more digestable chunks.

    There's a lot of press out there about the biodegradability of SAP (superabsorbent polyacrylate polymer)-loaded diapers, and it isn't encouraging. I believe there are some efforts now being made to make more biodegradable SAP, by loading it with starch, but I don't know how many brands of diapers do that. The general conclusion is that in a landfill, as I noted above, even allegedly biodegradable diapers don't biodegrade.

    So, no, I don't think anyone claims the stuff biodegrades quickly, especially when dug into a bed.


  • Miss_Moose (Winnipeg, Canda. Zone 2)

    After reading all the comments, I decided to really do some research. I wasn't sure if my husband knew a great deal about this, because the question was for the purpose of plant watering but I have to assume that if the salt in disposable diapers could harm the human body with an overdose of sodium, it would probably kill plants too. So I asked my husband about these products. I'm not a chemistry expert but he is (Ph.D. Organic Chemistry) and he told me:

    "Basically the stuff you get from diapers ( Sodium Polyacrylate [-CH2-CH(CO2Na)-]n ) has quite a bit of salt in it as you already know. It's a polymer and not likely biodegradable as polymers are robust and resist the action of enzymes to break apart the chains and degrade the compound. In table salt, there is an ionic relationship between Sodium and Chloride. The two have a -/+ bond. When introduced to water, the bond isn't strong enough to keep the two bound, and they float apart in the water. This is why the body can absorb the sodium. The sodium becomes digestible / processable by the body when it hits a glass of water or the water in the body's digestive system. The sodium in the absorbent medium found in diapers (Sodium Polyacrylate) behaves in the same way. As water hits the compound and it 'unravels as it absorbs water', the sodium breaks from the compound and floats, and in theory could also be absorbed by the body (and by plants) if eaten or fed to plants. Also a polymer, Polyacrylamide (-CH 2 CHCONH 2-) is stuff sold in garden centres for plant use, and it has no salt so it wouldn't overdose your plants with salt. However, there's no way to tell, considering the various compounds in plant food, how they would react to Polyacrylamide and if this product would retain some of those elements over time and cause problems. It's also interesting to note that just like disposable diapers, Polyacrylamide (the stuff made for plant use) is also a polymer, and likely not biodegradable."


    Here is a link about the absorbent stuff found in diapers and some fun facts on land-fill statistics as well as a 3-D map of the molecule and how the salt leaves the product as it gets wet:

    http://ymcichem.wikispaces.com/A+-+properties+of+disposable+diapers


  • daninthedirt (USDA 8a, HZ10, Cent TX, Sunset z30)

    Thanks for the expert perspective. That adds a lot!

    I find it odd that given that this stuff is approved for agriculture and presumably somewhat useful for agriculture, there isn't more information widely available about exactly how to use it or what it's good for.


  • Miss_Moose (Winnipeg, Canda. Zone 2)

    @daninthedirt I was surprised that the plant stuff wasn't really biodegradable. If it is advertised as so, then it must be only so in really specific conditions, or treated with something specific, or over a loooooong period of time. Just goes to show where the line is drawn on what something is, and what something isn't when advertised on packaging. Basically like calling something fruit juice when it only has 3% juice concentrate in it! Know what I mean?? :)

  • theforgottenone1013 (SE MI zone 5b/6a)

    Here's a different GW link from the one floral gave. Diaper Experiment

    I
    was thinking about taking the crystals from a diaper and mixing a small amount into
    some potting mix this year but can't get past the fact that they seem to
    last pretty much forever.


    Rodney

  • Miss_Moose (Winnipeg, Canda. Zone 2)

    Rodney thanks for the link, I went there and followed another link to this article from WSU:

    http://puyallup.wsu.edu/~Linda%20Chalker-Scott/Horticultural%20Myths_files/Myths/Hydrogels%202007.pdf

    Apparently, and trying not to load up with social-research vernacular, when the sample size for testing is small and the time period of the study is somewhat short-term, the gel made specifically for plants (Polyacrylamide) performs well. However, as mentioned the polymer would need to be treated with some kind of substance to break-down its properties, as it's resistant to natural biodegradability. Apparently according to the article, the plant food & treatments as well as UV light does just that. The polymer breaks down, but in a way to where its effects are lost before it's been able to perform its optimal duties in your garden or plant pot. Also, besides breaking down prematurely, it also nearly completely loses its active properties of water retention after the break-down process. I'm not sure if the amount it breaks down makes it safe to put in a "natural" landfill, but probably it would biodegrade better after it broke down after being exposed to plant treating materials and UV light. Heres a quote from the article:

    "It’s not surprising that polyacrylamide is rapidly broken down by decomposers; one
    study found the average size of the polymer to be less than 25% of the original in only
    14 days of microbial action. These gels contain a significant amount of nitrogen,
    which is often a limiting nutrient in both aerobic and anaerobic environments.

    In most outdoor applications, therefore, the functional life of polyacrylamides is
    short; this is borne out by a number of studies that have noted decreased efficacy of
    field-applied polyacrylamide gels over time. If gel activity is destroyed in as little as
    18 months, there should be serious reservations about its use in long-term landscape
    applications."

    So yeah, 14 days later the polymer is less than 25% of the original size. So in two weeks, the gel has broken-down to the point where it's almost completely ineffective. Also, and more concerning to me:

    "As the name suggests, polyacrylamides consist of many linked acrylamide units
    (monomers). Acrylamide is a known neurotoxin in humans and is suspected to be
    carcinogenic as well. During the manufacture of PAM gels, residual acrylamide is
    present as a contaminant and strictly regulated in the United States to levels no more
    than 0.05% or 500 ppm for agricultural use. However, an international study
    recommended that polyacrylamide gels used in cosmetics contain a residual monomer
    level of only 0.1 to 0.5 ppm. Therefore, the PAM hydrogels manufactured for
    agricultural and garden use can contain much greater concentrations of toxic
    acrylamide than that found in personal products."


    So the fact that the amounts of Acrylamide in PAM gels are potentially cancer-causing and also a proven neurotoxin are highly concerning to me. I'd certainly wear gloves and even a basic mask and eyewear if you don't mind looking like a mad-scientist when using this stuff. :/

  • daninthedirt (USDA 8a, HZ10, Cent TX, Sunset z30)

    When they're talking about exposure to UV light, they're talking about exposure to sunlight. So sure, the polyacryate on the surface will probably break down readily, but that dug under won't.

    Also, we were talking about acrylates. Acrylamides are quite different things, I believe. Are gels made specifically for plants the latter? I suspect we won't see suspected carcinogens anywhere near diapers. I see that cigarette smoking is a great way to consume acrylamides, BTW.


  • Miss_Moose (Winnipeg, Canda. Zone 2)

    @dan, you're right in the aspect that Garden Gel, the stuff sold specifically for plants, specifically named Poly-Acrylamide, would have to be in direct sunlight to suffer from UV exposure. Under the dirt, the UV would have no effect. However, as for this garden gel sold in nurseries, garden centres, etc. specifically for gardening and plant-benifiting water retention properties, other things effect the decomposition of the gel also, namely plant food and other compounds used in garden care, as well as apparently microbial properties in the natural decomposing process. So to be clear, while the diaper-gel is not as prone to decomposition, the garden gel is.

    Yes, the latter gel is made specifically for plants if that's what you were asking, which they sell at garden stores, and are the Poly-Acrylamide's. These are cancer causing and also a proven neuro-toxin according to the published article from WSU.

    So basically what my conclusion was, is that one should just write-off using "diaper-gel" (Sodium Poly-Acrylate, no proof of carcinogenic or neurotoxic properties found as of yet by myself and I would assume not since it's the active absorbing substance in disposable diapers), due to the sodium it can potentially deposit in your soil and into your plants, potentially killing them.

    And, one should also COMPLETELY write-off using the stuff bought at stores for plants, (Poly-Acrylamide, cancer causing and neurotoxic) for obvious reasons. One should take special caution if nothing else, and just know the risks and why there may be harsh warning labels on the containers. It has less to do with the physical "dehydrating/absorption" properties of the compound, and more with real chemical-contact dangers that have real implications for serious health risks. So basically, use at your own risk, probably not good to use for "fun garden projects" with the kiddos, and I would strongly advise protective wear when using such as gloves, and a cheap mask and eye wear to prevent inhalation and/or eye contact.

  • daninthedirt (USDA 8a, HZ10, Cent TX, Sunset z30)

    That's fascinating. Good discussion. Thank you. I guess your original question was about disposable diapers, but the ramifications of that question go well beyond them.


  • Miss_Moose (Winnipeg, Canda. Zone 2)

    Isn't that so true! I myself was really shocked to come to this conclusion! I think this knowledge should remain in healthy circulation in the community. I wish there was a way to de-salinate the diaper-gel. My husband mentioned vinegar which might do the trick, but then it would be very acidic, and I almost wonder if it would liquify the diaper-gel. I honestly got curious yesterday and tore apart an unused diaper, shook out the crystals and now have about 2 cups of gel. I'll add vinegar to it and see if it completely breaks down. If not, then perhaps the acidic properties could be neutralized with calcium carbonate, as other neutralizers are just basically made of more salt, such as baking soda, which would bring us back to square 1.

    I'll add some white vinegar to the diaper gel and update you in a bit. Who knows... perhaps we may end up with a safe, salt-free plant gel! Wanna get in on this patent?? Loll

    Update: I didn't realize it, but calcium carbonate separates and releases salt when it reacts with an acid. I didn't even think about it's hidden salt properties, since I didn't see Na in the compound structure. ( CaCO3 )

    Update: Vinegar turned the diaper gel into soup.

  • Dou Simon

    That is really a good content. Just want to share one thing: we can use super absorbent polymer (also called SAP) to help plants grow well--help them absorbing water. But potassium polyacrylate type SAP is much better than sodium polyacrylate type.

    References: SOCO Polymer

  • PRO
    outdoor living landscaping & design

    I've used it for years since 2010 works great used it in a green house operation, yes in trees, veggies, house plants it non-toxic, as far as its ability to absorb water yes it works wonders, does it absorb to much no and you do have to keep in mind how much room you have to work with think about that ,your root ball will take up space but we grow things hydroponically right, be aware of the plants needs doesn't need a lot of water the don't use this stuff. its non-toxic just be aware of what and where your planting any thing can be great just as well as being very bad it you the user its your stuff and you make the call. Side note I watered the heck out of that stuff never a problem and they do sell it in sheets so it can be easy to use. As with any thing thats not natural be careful with it and use personal safety equipment, rubber gloves a mask eye protection. its up to you to protect your self. I hope this helps from a real person using this stuff in the real world.

  • Tamara Soto

    I would like to point out that these SAP's seem to be harmful to earth worms. As the earth worm burrows it injests these crystals which expland rapidly when they are exposed to the moisture in the earthworm's body causing internal damage. So I would caution the use in ground.

  • Sean Smith

    I guess that soaking in demineralised (deionised) water, draining and replacing the demineralised water would reduce the amount of salt in the crystals. Alternatively, maybe the potassium polyacrylate is better since plants can use the potassium (I don't know if it's still too concentrated).

  • principalwisdom

    I created an account here for the sole purpose of connecting with Miss_Moose (Winnipeg, Canda. Zone 2) who approaches knowledge acquisition in much the same manner as myself. I greatly appreciate her comments in this thread. I'm going to run some experiments degrading diapers using sunlight: full direct, concentrated, diffuse, shaded, and (almost) complete darkness. My current questions are: What exactly will the end products be (gases, solids, liquids) when the sodium polyacrylate is fully broken down by UV? How will I accurately measure the UV decomposition of the samples? Perhaps by weight, assuming the sodium polyacrylate looses it's hydrophilic properties and whatever remains allows the water to evaporate.

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