What Are Hydrogels: Learn About Water Crystals In Potting Soil
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.
Water retention crystals, soil moisture crystals or moisture beads for soil 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?" Click here to learn more.
Hydrogel water crystals to beat drought
This is a product that goes by many different names: Polyter, Water Crystals, Orbeez, Watergel, Hydrogel, Hydrosource, Water drops, root watering crystals, super-absorbent polymers, PAM, water retention granules, hydrating crystals, water beads, water pebbles, hydrobeads, crystal soil, water jelly, jelly balls, soil moist, super slusher… The list seems endless and shows how much hope is set into this special product.
The only certainty about this topic is that we seem on the verge of a revolutionary breakthrough! Seemingly risk-free, these preparations in pellet or powder form promise wonders regarding water management. They’re said to help watering your pots on the balcony and help for large-scale agriculture. But truth be said, little is known about the long-term effects of hydrogels on soil, plant life, and animal life – us humans included!
Different types of hydrogel to grow plants
Even before modern science explored industrial manners of increasing water retention in soils, agriculturists were hoping to find ways to reduce runoff and make rainwater “stay there” for crops to use. There’s many different forms of irrigation, and modern hydrogels are assuredly the most recent development to date.
However, there are actually many different types of hydrogels. Let’s try to make sense of them.
One single word is the key to all of them: polymer!
But the devil is in the details, and not all polymers are as good as they sound…
What is a superabsorbent polymer?
All living things, from a material point of view, are built up from atoms that are associated to form molecules.
Many molecules are small – think “H20” for water here – but some are quite large, like the DNA that holds a transcript of most of our genes. Quite often, the larger molecules are actually a repetition of many smaller molecules, each dubbed a “monomer” that connect to form one long chain, the “polymer”.
A superabsorbent polymer is such a polymer that is special in how it reacts to water. It has the peculiar trait of having two very different states or shapes:
- when the surrounding environment is wet, the superabsorbent polymer will attract water molecules and wrap them around itself. It swells depending on how much water it can absorb.
- when it gets dry, the polymer will release the water and slowly bunch up. It returns to its original, dry, smaller, harder form.
These superabsorbent polymers, or hydrogels, are specifically designed to retain and release water in the hope of helping plants cope with irregular rain or irrigation.
Three major groups of hydrogels
Hydrogel material is always one of the following three major groups:
- natural hydrogel – this is derived from starch, extracted from crops such as corn and wheat. Often used in processed foods to influence structure.
- cellulose hydrogel – this comes from plant materials that contain cellulose. Usually mixed in with a small portion of petroleum-based products. Often used in health applications and cosmetics.
- synthetic hydrogel – 100% derived from petroleum (oil). Currently the cheapest available product category. This type is most often used in agriculture and horticulture.
Here are the differences among hydrogel polymers
- Polyacrylate vs polyacrylamide (or polyacrylamine)
- Sodium acrylates vs Potassium polyacrylates
- Cationic vs Anionic vs Neutral
- Natural or Biopolymer vs Synthetic
- Quality grade: Cosmetic, Food and Agricultural grade
- Manufacturing trust levels
Claims, facts and advantages of hydrogel
Hydrogel, miniature water cisterns in the soil
Hoarding water and releasing it slowly to plants around it is the primary claim that hydrogel manufacturers put forward.
A hydrogel, or superabsorbent polymer, is characterized by either of the following two metrics:
- how many times it can absorb its own weight in water
- how much it swells compared to its original, dry size.
For example, the children’s toy Orbeez ® claims it swells over 150 times the original size of the pellet.
A special cellulose-based hydrogel called Polyter ® claims it can absorb up to 500 times its initial weight in water.
Special polymers developed in laboratories reach ratios of up to 1,500! Such a capacity to retain water explains why they’re usually used in small amounts in agricultural applications. Usually, only a couple pounds or kg is enough for an entire field.
Theoretically, it should be possible to design water-absorbing polymers in such a way as to make it possible to never need to irrigate at all. All that’s needed is at least one day of natural rainfall in the year. All the water on that single day of rainfall could be absorbed by the hydrogel embedded in the soil. As time passes, it would slowly be released to the plants around it.
Hydrogel makes space for roots
Since they swell and shrink with each water cycle, the water crystals push the soil around them away and provide small crevices.
- In soils that are compacted, heavy clay soils, or in passageways where people always tread, this can be precious. Small nooks and passages help plants that have trouble developing a root system.
- This also increases air circulation. Bacterial and insect life is enhanced. Worms reappear.
Furthermore, this is particularly relevant when soils have been depleted of plant and animal life. Normally, worms and a bugs bore tunnels as they hunt and forage underground. However, in contaminated, dead soil, they’re absent and the ground stays packed. Hydrogel compounds are a solution to make plant recovery easier.
Hydrogel reduces runoff, erosion and evaporation
When gallons and liters of water pour down from the sky, usually only a fraction of it is absorbed by bare soil.
Most of it pools together and runs off, forming rivulets that drag away nutrients and smaller sediments. Soil is left bare and isn’t very nourishing. This is called erosion.
Since a single gallon of superabsorbent material can absorb hundreds or even a thousand gallons of water, much if not all of the water is captured on-site. It won’t collect to run off.
Water isn’t lost to evaporation since it’s held back in the crystals.
Hydrogel and roots fuse to form osmotic nodes
Roots have a gift in that they always find their way towards water. It has been observed that roots will always locate and colonize pellets or crystals saturated with water.
They’ll even grow in and around it to maximize surface contact, forming curious nodes that aren’t so common in the natural world.
The water retention of the hydrogel slush is high enough to prevent loss through evaporation, but not too high that roots can’t pull the water out. This makes it a great medium for the plants to grow.
Hydrogel can dispense needed nutrients or chemicals
When pre-loaded upon manufacturing, hydrogels can be infused with chemicals.
- Fertilizer, nutrients and even herbicides can be embedded in the polymer.
As water cycles in and out of the chain-like structure, some of these chemicals are leached out to the environment.
This confers precious properties to the hydrogels. Often it is used for good purposes, like Polyter, which adds organic fertilizer compounds to its cellulose-based polymer structure.
At other times, it’s used to spread poison, such as when Monsanto, recently acquired by Bayer, integrated synthetic polyacrylamides (a type of hydrogel made from petroleum) to herbicides. This ensured that the herbicide would stay put and take years to leach out into the ground, sterilizing land or killing off wild flora.
Safety, risks and dangers associated to hydrogel
Hydrogels in agriculture are very recent developments. There isn’t much research on the various dangers that might result from using superabsorbent chemicals over extended periods.
An in-depth review of hydrogel risks that have been considered:
- presence of acrylamine monomers in small amounts upon purchase – although harmless when multiple acrylamine polymers are bound together, single monomers have been found to foster cancer.
- slow release of acrylamine monomers as the product degrades – the polymer breaks down over time into its constituent monomers, but some types have been shown to interfere with reproductive hormones. Even if each molecule is broken down by microbes within at most two months, constant exposure may have an effect.
- Some agricultural water-absorbing crystals release sodium (salt) as they break down, eventually causing salinization.
- new chemicals used aren’t perfectly characterized – as with many experimental products, potential issues haven’t yet been extensively researched.
- physical swelling of hydrocrystals may plug or block intestinal tracts of animals and insects when ingested.
- many hydrogel products are produced in places that don’t have stringent environmental guidelines and industrial practices. Sometimes what is in the bag isn’t what is advertised.
Guaranteed wholesome alternatives
One particular study sought to clarify the importance of natural, organic soil amendments compared to hydrogel water crystals.
The conclusion was rather surprising: although using both manure and hydrogel did produce the highest results, pure manure came in a very close second.
The most advanced solutions such as Polyter strive to rely as much as possible on organic, natural materials. However, they’re still compelled to include some amounts of potassium polyacrylate. Even potassium polyacrylate may prove harmful to some degree, although it’s already much safer than sodium polyacrylate or other additives.
Why take unknown risks when proven solutions already work?
Great organic, healthy solutions to provide sufficient water and nutrients for your plants are already within reach.
- Mulch – the perfect solution, especially plant-based mulch like flax or pine bark mulch
- Compost – for nutrients, moisture and microbial life, this is unquestionably the best
- Ramial Chipped Wood – a revolutionary use for what is normally considered waste by the forest industry
- Peat – a great soil amendment that doesn’t have any negative impact where it’s used, although harvesting it isn’t yet fully sustainable. New sustainable products are as effective and can now be found in horticulture stores everywhere.
Along with ancient and modern irrigation solutions, this ensures that the soil in our gardens will stay as healthy as nature has intended it to be!
Hydrogel crystals are a revolutionary way of dealing with water stress in the garden. Promising to eliminate watering altogether, this technology is useful.