What Are Hydrogels: Learn About Water Crystals In Potting Soil

What Are Hydrogels: Learn About Water Crystals In Potting Soil

By: Mary H. Dyer, Credentialed Garden Writer

If you’re a home gardener who spends any time browsing in garden centers or on the Internet, you’ve probably seen products that contain water retention crystals, soil moisture crystals or moisture beads for soil, which are all just different terms for hydrogels. Questions that may come to mind are, “What are hydrogels?” and “Do water crystals in potting soil really work?” Read on to find out more.

What are Hydrogels?

Hydrogels are small chunks (or crystals) of man-made, water-absorbing polymers. The chunks are like sponges – they hold a tremendous amount of water in comparison to their size. The liquid is then released gradually into the soil. Various types of hydrogels are also used in a number of products, including bandages and wound dressings for burns. They are also what makes disposable baby diapers so absorbent.

Do Water Crystals in Potting Soil Work?

Do water retention crystals actually help keep soil moist for longer periods? The answer is maybe – or maybe not, depending who you ask. Manufacturers claim the crystals hold 300 to 400 times their weight in liquid, that they conserve water by releasing moisture slowly to plant roots, and that they hold up for about three years.

On the other hand, horticultural experts at University of Arizona report that the crystals aren’t always effective and may actually interfere with the water-holding capability of the soil. The reality is probably somewhere in the middle.

You may find the crystals convenient for keeping potting soil moist while you’re away for a couple of days, and they may extend watering a day or two during hot, dry weather. Don’t expect hydrogels to serve as miracle solutions for extended periods of time, however.

Are Moisture Beads for Soil Safe?

Again, the answer is a resounding maybe, or maybe not. Some experts say that polymers are neurotoxins and they may be carcinogenic. It’s also a common belief that water crystals aren’t environmentally safe because the chemicals are leached into the soil.

When it comes to water retention crystals, they are probably convenient, effective, and relatively safe for short periods, but you may choose not to use them on a long-term basis. Only you can decide if you want to use soil moisture crystals in your potting soil.

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I’ve always wondered: are water crystals bad for the environment?


Lecturer - Environmental Health and Management, Western Sydney University

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Michelle Ryan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.


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This is an article from I’ve Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to [email protected]

Are water crystals bad for the environment? –Terry Gilmour

This is an excellent question, and something an environmentally conscious gardener might wonder. With changing rainfall patterns, drought and an increasing average temperature in Australia many people are looking for ways to save water in their garden, and adding water crystals to your soil appears to be a good solution. But what do we really know about water crystals and are they bad for the environment?

Well, you can put your mind at ease: water crystals are not bad for the environment. In fact, in other forms they are actually used to help protect the environment.

Yates Waterwise Water Storage Crystals

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When added to potting mix or garden soil, the crystals absorb up to hundreds of times their own weight in water. This water is then released back to the plants over time as they require it. The crystals reduce water wastage, increase the time between waterings and promote improved plant survival during dry times. The crystals are effective for up to 5 years, then biodegrade harmlessly.


  • Can be used in both potted plants and garden beds, to store water and to keep plants healthy
  • Water storage crystals prevent the soil drying out, improve soil aeration and drainage
  • Water crystals rehydrate themselves with each watering, lasting several years before biodegrading harmlessly
  • Using water storage crystals, plants can tolerate drier weather conditions and less frequent watering

Wet mixing (recommended):

Mix one teaspoon (5g) into 750ml water. Leave for an hour before mixing into 5L of potting mix. Increase to two teaspoons per 5L for hanging baskets and other water stress-prone plants.

  • Plants already potted or inground: poke vertical holes into potting mix or drip line and place a small amount of into the base of each hole. Water in thoroughly, then top with potting mix
  • Sowing seed: mix 10g per m2 into top 50mm of topsoil, sow seed and water in thoroughly
  • Laying turf: evenly spread crystals at 10g per m2, lay turf then water

Mix one teaspoon (5g) of crystals with 5L of potting mix. Pot up plant and water in thoroughly. For best results, water two hours later to ensure crystals are fully charged. It is safest to use the crystals wet instead of dry as the crystals take up substantially more volume once wet.


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93% quartz crystal, ground & sourced from the mining industry. The material would likely end up in land fills. The remaining components are resin and dyes. Either acrylic or polyester and similar in composition to the resins used in filling our teeth so quite inert. The quartz, resin & dyes are mixed together in proportion to create the various patterns and colourways. Some would be formulated, ground again & then re-suspended to create the complex colours. The mixture has the consistency of cookie dough. It is then subjected to high pressure presses/tables. Once hardened, the surfaces are ground & polished or etched depending upon the pattern. As a result there are unusual colours and textures available that are not naturally occuring. Granite is a combination of feldspar, quartz, mica. Formed metaphorically, is subject to high heat & pressures from geologic activity on our earth. Due to the minerals and action of a particular area, a stone can be so unique its not found anywhere else on the planet. Once a quarry has been mined, it is closed & unless a similar formation is found, may never be repeated. Due to its nature, a piece of stone could be similar to others from its "block", much like a loaf of bread. It is always important to buy the stone necessary all at the same time from the same block, or it can be very difficult to match. Both are fabricated in a similar fashion with stone cutting tools & CNC equipment. Because granite and marble are conglomerates, they sometime require mesh reinforcing to hold the divergent stones together. These are typically the more dramatic stones. This factor can limit the overhangs possible for bars etc without necessary support corbels. other than that.. it pretty much comes down to the look.

Best way to keep shower glass clean?



How did your granules end up on top of the soil? Do you cultivate your soil a lot or do they work their way up? Anybody else gardening in sand? I know many of you have caliche. I used to curse my clay but would sure love to have some right now. Getting my hands on any organic material to hold moisture in the sand is very difficult here.


We have an alkaline clay soil. It was not worked after the granules were dug in at planting time. Therefore, they simply worked their way up (floated) to the top of the soil.


Harley Lady, the crystals are constantly shrinking and expanding in reponse to moisture levels. When they expand they displace soil (more displacement occurs above than below them as that is the path of least resistance), when they shrink, the heavier soil fills in the void that develops around them. Eventually, this constant shrinking and expanding will cause it to work its way to the surface.


I can't hold any moisture in my ground. There are very few sources of organic material here and what is available is very expensive. I compost my household waste but the desert yields little in the way of compostable materials (no lawns, few leafy trees). When I go up to the USA I bring back sacks of amendments but it's never enough.

Rather than mix the granules into whole planting areas, I'm going to try mixing them only into the area below the rootball in the planting holes. I don't expect miracles from them, just a little help. My water comes in a tanker truck, not through a pipe, so you can imagine how precious it is. I can't afford to waste a drop.

Has anyone seen any difference in the performance of the various brands or is price the only consideration?


I use them in my wall planters, I'm in Phx so the block wall gets very hot and small terra cota planters evaporate quickly. Since using the crystals the plants have done much better! I suggest soaking them 1st and then mixing with the soil :)


If you can auger out some fairly deep holes into your plants' root systems without damaging the plants, you can mix the crystals with some potting soil or compost and cram that into the holes. It's not ideal, but it may help. Also, I once bought a big bag of compressed coconut shell fiber that was the size of a big bag of potting soil, but when you put a chunk in a bucket and add some water and fluff that up with a hoe or rake, it expands in volume like you wouldn't believe. I got mine at a nursery, but I've seen it advertised for pet bedding. It retains water well and is a good soil amendment. It's marketed as a renewable replacement for peat moss, but it doesn't repel water when it's dry like peat moss does (frankly, I don't think it holds water quite as long, either, but it definitely helps). I suggest it for you because I figure you can only haul back so much soil amendment per trip, and this stuff is really compressed- more bang for your transport buck, as it were. If I can find it online I'll post a source. If you were to mix the coir (that's the coconut shell stuff) with the crystals it would help you out a lot, especially for your potted stuff in the Baja Norte sun.


Good luck- if you do a Google search and type in "coir coconut fiber" you'll get a lot of information- a whole lot!


G_t thanks for the suggestion regarding pre-soaking them.

Eileen, good idea re: putting polymers right *into* the rootball and excellent suggestion of using coir. You know, I have seen it but never bought it in the PNW because there was so much other organic material readily available at low cost. It never even occurred to me to use it down here. Appreciate the links and I'll check those out and get some my next shopping trip to the States. I'll report back how it works for me.


Good- and I appreciate your trying to enrich the Baja soil! I think I must have lived there in a former life- it feels so simpatico to me whenever I go there, wherever I go there.


Hey, next time you come down this way, you *must* stop and see me. I get so lonely for "green" companions (hmmmm should that be greengos? ) We can talk plants and go visit my friend, a little old Mexican man that grows some cool stuff and see his shade houses and see his carvings before hitting the beach with a cold one.


I ordered some watersorb polymers last winter and have used them all season for my transplants as well as in my veggie garden. the pkg tells what the ratio should be and I simply increased it for plants that prefer more moisture.

It seems to work I did not use any for the okra and peppers and the dirt there did get dry and hard (which they can tolerate) while the tomatoes seemed to stay evenly moist.

I did a lot of shopping and they were the best price at the time, also their product doesn't break down into salts as some others do.

I haven't had any resurface :) and have applied them in both the granular and rehydrated forms. they do come in different sizes for different applications and larger granules may be more prone to working up to the surface.

Send your address and I'll mail you a baggy - a little goes a long way - I think it's a tbsp for a tree transplant.

No teacher like experience :)


Anna, that's very kind of you. I'd love to try them. pls check my trade list and see if there is something you might like to try in that new GH of yours !


I love it.
Let us know how it works!


I've used these crystals in my dry soil (Dry for Georgia, that is. My sandy clay is more stable than your sandy soils, but still, it has never migrated to the surface. part of the reason is that I NEVER put it above the level of the root ball, always below. I dig the hole deeper than "necessary", and water rarely but deeply, with a slow trickle from a hose, once a week or oncc every two weeks, even when establishing a plant, and not at all after that. It is my belief that doing this creates a moist zone BELOW the roots of the plant, but not TOO FAR below. This encourages the plants to root more deeply than they would otherwise, and makes them more drought tolerant. This is all uneducated theory (speculation) on my part, I have no scientific evidence, but the plants I have done this well have prospered. Uf the crystals migrate upwards later, and there aren't too many of them, it won't be a problem. Their main purpose, in my mind, is to encourage the deep penetration of roots. Perhaps choosing an organic mulch to mix in BELOW the root ball might help do much the same thing. I generally make a 3 to 4 inch layer of "treated" soil below the root ball of a small plant, or as much as a foot below a small tree that I plant. This is partlally because there is rock below a very thin vineer of very poor soil in my front yard. I'm basicly building a container with a pickaxe. I've gotten around this problem, to a large extent, by building terraces on my steep hills, and filling in the level by adding organic rich garden soil trucked in a dump-truck load at a time. I've used 1 1/2 so far fir the largest terrace in my front yard, and am ready for one more load for a terrace in my back yard. I'll need 1 more, to finish my third terrace later this winter. Then my problem will become too much shade, instead of too much sun, and my new environment will render many of my plants inappropriate. Lots of my plants are relatively easy to move. Yucca, Iris, Carolina Jasmine. I actually like AZ plants, since they're drought tolerant, and many are freeze tolerant. I'm growing red yucca from seed, and hoping that they will prosper in my sunny dry areas. They did very well the first year. No flowers yet, but I can't wait to see how they do.


I am learning to garden in sand (having recently moved to western Queensland) Our vegetable garden is barely 3 months old and is producing something, though probably not for much longer as all annuals die off (or so I am told) after Christmas. We made raised beds of sand topped off with a layer of compost. Before the small log edged beds were filled we lined them with plastic, after making drainage holes. then the beds were saturated with water. The seedlings were mulched very deeply - 30+cm. and protected with milk cartons or yogurt pots with the bottoms and tops removed. Seeds were also directly sown and covered with damp hessian (these areas were watered once a day until the seeds sprouted and the seedings established.I find that I only need to water every 5 to 7 days once the seedlings are established depending on the humidity which can be very low.
I have only used the granules in a few hanging baskets, which are going to be the basis of a cooling bush house/fernery when we buy a house in the near future. The granules seem to work well and I water these only every other day, without the granules I do not think the soil would retain the moisture at all and would have to be watered several times a day, even with mulch, and deep shade.
Mulching hay is prohibitively expensive at the moment if it is available anywhere, and we have collected mulga leaves from the bush which is better than nothing. I have also started a worm farm - would that be possible for you to do, the worm castings have a great affinity to water.
I forgot to say that the raised beds help to drain the salts out of the town borewater eventually in our permanant house garden we want to use rainwater only, or at the worst diluted town water.
Pits lined with platic might work with you if you have no problem with qater quality
Charleville, Qld


I live in the SF Bay area and had to have a lawn for my day care kids (this was 20 years ago). Before we laid down the sod we added polymer granules to the topsoil. It was a huge success. I had to water about a third as often. I used them also in raised beds to good effect. Polymers break down over time and dissipate, but I've found them clinging to roots of shrubs I'm pulling out or moving years and years later. I find that they move to to top more frequently in pots. If you do buy them, go to the manufacturer and buy in bulk. My friends and I bought a 50 lb sack, divided it up, used it and I still have a 5 gallon laundry tubful in my garage.


I unknowingly have been using these crystals to make "air gel" room fresheners. I had no clue they were really from the garden world. I hear two ounces absorbs up to a gallon of water, (and a little fragrance oil) and are poured into small and wide mouth mason jars with a round lace top for ventilation. I feel they work well for dorms and areas that do not allow candles.

But recently, I travel allot and was desperate to incorporate some kind of water retention system in my container gardens. I simply pre-mixed the Polymer, waited and hour and then mixed it in with rock 1/2 way up my containers. I mixed nutrients in that, to be sure. I then added the potting soil and plants. So, far I think my garden's can withstand a good week without me, and I have not seen any crystals floating up. I think they are an awesome attribute if used right and CHEAP!

I feel they have the attribute of absorbing nutrients and other controls, that may operate under a kind of "timed released" theory if you mix them up first and wait for them to expand. And yes, I am also working with sand, in Florida.

I see florists also use them to make water gardens and fresh cut floral designs around them.

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