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Friends see the lush green plantings at our house and exclaim, “Oh, you have such a green thumb! What’s your secret?” I say, “I water them,” and they look at me in disbelief. But watering – not watering enough, or watering so much that plant roots get soggy – may be the biggest issue for those who think their thumbs are black. Fortunately, it’s often an easy problem to solve. Polymer moisture crystals are one of the best watering aids I’ve found.
Polymer moisture crystals are like magical little garden helpers. They mop up little puddles of water around roots so plants don't drown. They release the water back to the roots as the surrounding soil dries out, keeping plants from wilting between waterings or rainfalls. If you price them by weight or volume, they seem expensive, but a little bit goes a very long way. They take about 3 years to break down, so they'll last a while in your garden, too.
Polymer moisture crystals look like coarse salt crystals. They absorb up to 300 times their own weight in water, until they look like little cubes of jello (see photo above). They then release the water slowly back to the soil, keeping it evenly moist between waterings. Good drainage is still important, but by absorbing excess water the crystals help guard against the "wet feet" that make many plants unhappy.
Polymer moisture crystals are a boon to container gardeners. Without moisture crystals added to my potting mix, I could water containers on my sunny deck twice a day, and I'd still have drooping, thirsty plants. By using the crystals, I can even skip a day once in a while, especially if it's not really hot outside. I always add them if I'm planting a container for a non-gardening friend. Since they help protect against both overwatering and underwatering, the crystals allow for beginner inconsistencies.
Garden transplants benefit from polymer moisture crystals also.[1] You can till them evenly into the top 6 inches of the garden bed, or you can sprinkle them down into planting holes. In a few seasons, according to the manufacturer, they will break down harmlessly into nitrogen, carbon dioxide, and water. They are nontoxic and safe to use on food crops.
The crystals are also helpful for putting in new lawns or areas of ground cover. When I plant creeping thyme along the edge of a bed or a walkway, I scratch a sprinkling of moisture crystals into the soil around the plants. The extra moisture held by the crystals encourages runners to root and form new plants for additional coverage. If you're putting in a new lawn, adding polymer moisture crystals before broadcasting seed or laying sod will provide an extra moisture boost for the first few years and get your new turf off to a great start. Be sure to water long and deeply, so water gets down to the roots and so the crystals have a chance to soak up some extra moisture.
I add polymer moisture crystals to my potting mix for starting seeds or propagating cuttings, where keeping an even moisture level can be crucial. A smaller size crystal is nice for shallow seedling trays, and you can break the crystals down to a finer texture by putting them in a propeller-type coffee grinder. Sifting afterwards to remove any finely powdered crystals is helpful.
Powdered moisture crystals have their own uses, and you can purchase powdered polymer or reduce regular crystals to powder in a coffee grinder (take care not to ingest or breathe in the powder). Rehydrated into a slurry, powdered polymer makes a great root dip for bare root transplants. When I wrap bare root plants for shipping, I put a slap of rehydrated polymer onto a moist paper towel and wrap it around the root ball before wrapping the roots in plastic.
How much should you use? When you're adding polymer moisture crystals, it pays to follow package directions. More is not better! Adding too many crystals to a pot can result in plants heaving right out of the container as the crystals swell with water. Add enough of them, and after a good rain you'll see a "snowfall" of jello cubes spilling from your containers out across your patio. Even without overdoing it, you may see a few swollen crystals on the surface of your soil or potting mix. If you don't like the way that looks, just use a couple inches of plain mix to top off your pots.
Both SoilMoist and Watersorb post application rates on their websites. It works out to about 2 teaspoons per gallon pot (less for a "trade gallon"), or 2 rounded tablespoons per 5 gallons of potting mix. With transplants, I sprinkle about 1 tsp. in the planting hole for a 6 inch pot or for a tomato seedling. When planting out from 2 to 4 inch pots or for smaller plants like peppers and basil, I sprinkle about ½ teaspoon in the hole. The application rate is roughly the same as for pelleted, time-release fertilizer (such as Osmocote or Dynomite). In fact, I often mix a jar of half fertilizer pellets and half moisture crystals to use when I plant out seedlings.
Where can you buy polymer moisture crystals? Nurseries, home improvement centers, and mail order companies carry 8 to 12 oz. jars of brands such as SoilMoist. For great prices on 2 pounds or more, check out Watersorb.com. There have also been DG co-ops for Watersorb.
The single best thing you can do for your plants is to give them enough water. Adding polymer moisture crystals is an effortless way to give your plants an extra water supply. I've used them in potting mix, in my clay soil, and in my in-laws' sandy soil. Of all the gardening aids and culture techniques I've tried, using polymer moisture crystals has made the biggest difference to the vigor and success of my plants. If you don't use them already, I hope you'll give them a try this summer. They really work!
Thanks to Bluekat76 for the use of her "oops too much" photos. Other photos in this article are by the author.
[1] University of Florida studies in 2000 and 2001 showed that the addition of Watersorb increased yield and net revenue for tomato crop by 5%, peppers by 24%. See this summary by Polymers, Inc.
About Jill M. Nicolaus
Better known as "Critter" on DG, Jill gardens in Frederick, MD. This week, I've been cutting lavender, putting up pluots (plum-apricot fruits), and pulling weeds (always, LOL). I love being outside in the cooler morning -- coffee cup in one hand, watering hose in the other -- watching the birds and butterflies among the flowers.(Images in my articles are from my photos, unless otherwise credited.)
Posted by bpatnode (from Iowa Park, TX) on June 7, 2008 at 12:47 PM:
dear sir, I am looking for the polymer moisture crystals, does your company carry this product. if so could you please let me know by e-mail, do you have a catalog about what you sell about garden supplies if so would you please send me a catalog to this address Carol Patnode 106 south pacific ave. Iowa Park texas 76367 thank you sir .June 7th 08
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Posted by critterologist (from Frederick, MD) on June 7, 2008 at 2:40 PM:
Welcome to DG, Carol! Dave's Garden isn't a company that carries products, although Dave recently set up a new "Marketplace" feature where plant-related items can be bought and sold, e-Bay style.
I can't send you an email since you didn't include your email address above, so I hope you'll log back on to DG.
In the article above, I included a link to one of my favorite vendors, watersorb.com. They're a great source for the polymer moisture crystals.
Happy Gardening!
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Subject: Examples of moisture crystal uses
Posted by gardenwife (from Newark, OH) on May 14, 2008 at 2:08 AM:
I ran across this page and thought the photos were interesting. Check out the crystals in the Coca Cola glass. LOL
[HYPERLINK@www.aquadiamonds.com]
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Posted by critterologist (from Frederick, MD) on May 14, 2008 at 7:45 AM:
Cool site! Thanks
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Subject: Polymer Moisture Crystals by Jill
Posted by marciabeppler (from State College, PA) on May 13, 2008 at 11:54 AM:
Hi Jill: Just want to say thank you for the info. I have been using these crystals for two years now and have found them invaluable! I agree with you that the price seems high, but I believe these crystals are really worth it. I especially laud you for the detail about their use and your photos contribute a great deal too. I am becoming a dedicated user for two good reasons. I am doing more and more gardening in "patio pots" thanks to these crystals helping my pots survive periodic neglect by me, and now YOU and your good information!!!
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Posted by critterologist (from Frederick, MD) on May 13, 2008 at 12:18 PM:
Thanks for the kind words!
The price is better if you go to the watersorb website, and a pound of crystals really will take care of a lot of pots. :-) After several inches of rain here the past couple of days, I'm seeing some crystals on top of my pots that are half again as large as the ones in my close-up shot (and those are the ones where a rounded teaspoon of crystals absorbed 2 1/2 cups of water!). Good stuff!
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Subject: Presoaking crystals
Posted by philipw2 (from Chevy Chase, MD) on May 9, 2008 at 5:39 PM:
I use the crystals when I plant shrubs and other valuable plants in my yard which is dominated by dry shade. The result is that my shrubs rarely exhibit wilting etc.
I soak my crystals ahead of time. That way they will not compete with the plant for moisture and they expand more fully. (This last claim I remember from an article in Horticulture or some other garden rag from 15-20 years ago.)
Glad to read your article. I have been using way too much of this stuff. I'll remember for the future. $$$
Thanks for the pointers.
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Posted by critterologist (from Frederick, MD) on May 9, 2008 at 6:23 PM:
Presoaking is also a good way to see just how many crystals you're really adding. Good point!
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Posted by Soulja (from Louisville, KY) on May 10, 2008 at 6:51 PM:
great point, and Great Article! I have been waiting for all that info on that subject laid out just like that.
perfect. Thank You!!!
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Posted by critterologist (from Frederick, MD) on May 10, 2008 at 7:06 PM:
I'm glad it was useful! :-)
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Posted by gardenwife (from Newark, OH) on May 14, 2008 at 2:03 AM:
At one site, aquadiamonds.com, they said to soak the crystals in water for 12 hours, then drain them in a colander for 1/2 hour or more. Here's the page: [HYPERLINK@www.aquadiamonds.com]
This message was edited May 14, 2008 2:05 AM
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Posted by critterologist (from Frederick, MD) on May 14, 2008 at 7:45 AM:
Too much prep work for me, but it's a good place to start if you're uncertain about the amount to add, especially if you're doing little pots where volume really matters.
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Posted by Soulja (from Louisville, KY) on May 14, 2008 at 8:28 AM:
What do you think Miss Critterologist about these and potential roles for upside down tomatoes growing from an arbor barrels, which need to be watered very slowly? I'm trying different systems for watering them like hanging cups over the individual plants with tiny holes poked in the bottoms for slow delivery, to Aqua Globes (for gosh sakes)! I'm not sure I trust those.... some empty fast and some slower....
I know these Watersorb crystals which I ordered just after reading your article can help but for now, any watering advice regarding these.... maybe plants in the top to absorb heavy rain, or keep the tops covered like they are now and rely on the crystals to distribute moisture.... any sort of drip systems you all know of....
I can't logistically stand on the ladder for an hour dripping drops on these dry pots.... ; )
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Posted by gardenwife (from Newark, OH) on May 14, 2008 at 11:02 AM:
Oooh, I would think those would work great for the upside-down planters. Great idea! I might try one this year, just because watering will be easier. I ordered from WaterSorb directly last night and I'm stoked. LOL
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Posted by critterologist (from Frederick, MD) on May 14, 2008 at 11:30 AM:
I haven't tried the upside down planters. But when I want to water a pot really thoroughly, I add smaller amounts of water repeatedly, to give the crystals a chance to soak it up rather the excess rather than just having it run through. That gives the pot a sort of reservoir of extra moisture in the expanded crystals.
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Subject: OOPS
Posted by cathy4 (from St. Louis County, MO) on May 8, 2008 at 12:00 PM:
Haha, I just went outside when the rain let up a bit to add some diluted fertilizer to some plants and found jello on the top of the soil with the baby hostas I potted up this week. It looks funny, guess I used too much this time. It gets much bigger than I thought, wow!
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Posted by critterologist (from Frederick, MD) on May 8, 2008 at 11:37 PM:
LOL... even when you use the right amount, a few chunky "jello" pieces seem to work their way to the soil surface after a good, soaking rain. In the photo at the top left of the article, you can see just how big those little crystals will swell up!
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Subject: A "swell" subject!
Posted by darius (from Marion, VA) on May 8, 2008 at 2:51 AM:
Jill, Thanks for the article. I knew about Watersorb crystals... even bought some from a co-op here a while back. But they got packed away in a move and totally forgotten... until now. I can see what a boon they can be for uses other than just potted plants that dry out rapidly, especially when used for shipping plants, and transplanting seedlings.
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Posted by bluekat76 (from Ijamsville, MD) on May 8, 2008 at 4:43 AM:
Another great article Jill! I remember laughing so hard when I say my gardens with "jello" on top. Didn't hurt anything that year it just looked funny for a little while. I love the crystals in my containers though. I got them from the co-op too Darius.
-Kim
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Posted by critterologist (from Frederick, MD) on May 8, 2008 at 6:57 AM:
:-)
I just think they're a wonder. It's amazing to me that the rounded teaspoon of crystals in the photo at the top expanded to hold two and a half cups of water!
I ordered 50 pounds last year and split them with a friend, so I didn't need the co-op this year, either. LOL
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Posted by cathy4 (from St. Louis County, MO) on May 8, 2008 at 9:28 AM:
Here's another happy user. We had little rain last summer, but my potted plants did great. They are in the veggie garden this year and I'll be working them in around established plants when possible.
I used them on the garden at church that gets once a week watering, never more, and it looked great all summer.
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Posted by tcs1366 (from Itasca, IL) on May 8, 2008 at 12:02 PM:
Great article Jill.
funny thing... last year some spilled on my patio and after every rain, even this morning... i see this lil [sometimes BIG] mound of jello that has been pushed towards the foundation ... I pick some up, but obviously miss some, as the mount of jello is still there.
great stuff by the way.... and love the idea of using it to ship plant, to keep the roots damp.
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Posted by cathy4 (from St. Louis County, MO) on May 8, 2008 at 12:13 PM:
Keep a few for youself and if you like, send some to the troops.
If you spill them on the floor in the kitchen, use the vacuum to pick them up, not the mop, lol. I learned this the hard way....
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Posted by tcs1366 (from Itasca, IL) on May 8, 2008 at 12:18 PM:
>>not the mop, lol. I learned this the hard way..
ROFL -- i bet!!
I've seen those "Neck Ties" -- great idea, and a great cause too.
I've also seen the crystals used in dog beds to help keep the pooch cool on hot days.
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Posted by critterologist (from Frederick, MD) on May 8, 2008 at 12:56 PM:
Yes, the cool ties are great!
Bluekat, thanks again for letting me use the garden photos! :-)
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Posted by cathy4 (from St. Louis County, MO) on May 8, 2008 at 1:02 PM:
So all I have to do is dig the sewing machine out of the "office" and I can use up some of the 3 pounds I bought, waaaaay to much for my garden, what was I thinking?
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Posted by critterologist (from Frederick, MD) on May 8, 2008 at 7:14 PM:
You were thinking, "I won't need to buy these again for a couple of years."
:-)
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Posted by carrielamont (from Milton, MA) on May 8, 2008 at 8:56 PM:
So what are X and Y that they break down into? Can I grind them in a blender (don't drink coffee at home)? I think I'm a convert. Thanks Jill, for a clear, informative article.
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Posted by critterologist (from Frederick, MD) on May 8, 2008 at 11:17 PM:
Yikes! Carrie, thank you. I'm not sure how that happened... "X and Y" were placeholders I was using in an earlier version of the article while I double checked what the websites said about the breakdown products (nitrogen, carbon dioxide, and water)... somehow, that phrase got back into the text! I've corrected it. Thanks for spotting the problem!
I haven't tried using a blender to do the grinding, but I don't see any reason why that wouldn't work as long as you could get every bit of it rinsed out afterward (a blender, unlike a coffee grinder, is used wet... so any leftover powdered crystal would hydrate and maybe gummy things up).
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Posted by carrielamont (from Milton, MA) on May 9, 2008 at 9:49 AM:
Oh, I thought it was part of the text! Seriously!
I think I get what you say about blenders - it's hard to understand how incredibly absorbent these little innocuous-looking moisture guys are. But imagine mixing some into your smoothie!
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Posted by cathy4 (from St. Louis County, MO) on May 9, 2008 at 9:52 AM:
NEW Weight Loss Discovery! 1/4 teaspoon and you are full all day. I'm kidding, do not eat these.
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Posted by carrielamont (from Milton, MA) on May 9, 2008 at 10:27 AM:
Accidentally mixing some into your smoothie; having some end up in your smoothie by some horrible mistake. I was not clear enough for some, Cathy! (smirk.)
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Posted by critterologist (from Frederick, MD) on May 9, 2008 at 11:05 AM:
You also really, really don't want to breathe this stuff into your lungs... that's probably a warning I should add when talking about the powdered polymer.
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Posted by carrielamont (from Milton, MA) on May 9, 2008 at 12:42 PM:
Certainly no laughing matter.
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Posted by critterologist (from Frederick, MD) on May 9, 2008 at 1:17 PM:
For sure. I've added a comment about it to the article.
Thanks, everybody, for your input! I really love the interactive format of online publishing.
:-)
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Posted by crimsontsavo (from Crossville, TN) on May 9, 2008 at 1:42 PM:
I must have this stuff.
I was using diaper guts from (clean) diapers boo was too big for, for my bonsai.
I wonder if walmart or lowes carries these. Hmm.
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Posted by critterologist (from Frederick, MD) on May 9, 2008 at 1:51 PM:
The stuff in diapers will work in a pinch (you can use clean diapers to line hanging baskets, too), but it breaks down quicker, so I think it's really only good for single season use. Lowe's should have the crystals, probably as "Soil Moist," but ordering from Watersorb.com is a lot more cost effective.
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Posted by crimsontsavo (from Crossville, TN) on May 9, 2008 at 2:48 PM:
Ill check their website. Thanks!!!
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Posted by gardenwife (from Newark, OH) on May 14, 2008 at 1:58 AM:
Great article, Jill -- thanks for posting about it. I found the co-op thread from 2007, albeit a little late, and then found this article.
This year, I'm doing more containers and I want to use WaterSorb in them and in the planting holes of the annuals I'm putting in the ground. They seem to have good prices for the amount you get. Like you say, they go a long way.
Have any of you used straight hydrated crystals for rooting cuttings? I read at one manufacturer's site that you can use them for that purpose. It sure would make it easier to monitor the root development! LOL
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Posted by critterologist (from Frederick, MD) on May 14, 2008 at 7:44 AM:
I haven't done that yet but have heard about it.. I think there's even somebody marketing a combo with crystals and rooting hormone.
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Posted by gardenwife (from Newark, OH) on May 14, 2008 at 11:03 AM:
Well, hey, I have Rootone and I'll give it a whirl. I have some fuchsia and impatiens I want to root, so they'll be my test subjects.
Polymer moisture crystals are like magical little garden helpers. They mop up little puddles of water around roots so plants don't drown. 
They release the water back to the roots as the surrounding soil dries out, keeping plants from wilting between waterings or rainfalls. If you price them by weight or volume, they seem expensive, but a little bit goes a very long way. They take about 3 years to break down, so they'll last a while in your garden, too. 
Polymer moisture crystals are a boon to container gardeners. Without moisture crystals added to my potting mix, I could water containers on my sunny deck twice a day, and I'd still have drooping, thirsty plants. By using the crystals, I can even skip a day once in a while, especially if it's not really hot outside. I always add them if I'm planting a container for a non-gardening friend. Since they help protect against both overwatering and underwatering, the crystals allow for beginner inconsistencies. 
The crystals are also helpful for putting in new lawns or areas of ground cover. When I plant creeping thyme along the edge of a bed or a walkway, I scratch a sprinkling of moisture crystals into the soil around the plants. The extra moisture held by the crystals encourages runners to root and form new plants for additional coverage. If you're putting in a new lawn, adding polymer moisture crystals before broadcasting seed or laying sod will provide an extra moisture boost for the first few years and get your new turf off to a great start. Be sure to water long and deeply, so water gets down to the roots and so the crystals have a chance to soak up some extra moisture.
I add polymer moisture crystals to my potting mix for starting seeds or propagating cuttings, where keeping an even moisture level can be crucial. A smaller size crystal is nice for shallow seedling trays, and you can break the crystals down to a finer texture by putting them in a propeller-type coffee grinder. 
Sifting afterwards to remove any finely powdered crystals is helpful. 
How much should you use? When you're adding polymer moisture crystals, it pays to follow package directions. More is not better! Adding too many crystals to a pot can result in plants heaving right out of the container as the crystals swell with water. Add enough of them, and after a good rain you'll see a "snowfall" of jello cubes spilling from your containers out across your patio. Even without overdoing it, you may see a few swollen crystals on the surface of your soil or potting mix. 
If you don't like the way that looks, just use a couple inches of plain mix to top off your pots. 
Where can you buy polymer moisture crystals? Nurseries, home improvement centers, and mail order companies carry 8 to 12 oz. jars of brands such as SoilMoist. For great prices on 2 pounds or more, check out Watersorb.com. There have also been DG co-ops for Watersorb.
The single best thing you can do for your plants is to give them enough water. Adding polymer moisture crystals is an effortless way to give your plants an extra water supply. I've used them in potting mix, in my clay soil, and in my in-laws' sandy soil. Of all the gardening aids and culture techniques I've tried, using polymer moisture crystals has made the biggest difference to the vigor and success of my plants. If you don't use them already, I hope you'll give them a try this summer. They really work!
