Are Water Absorbing Crystals Good Plants? How To Use Them?

There are so many new technologies and tools available today to keep your plants healthy. Among them, we have water-absorbing crystals. They are used to store water and reduce the need for watering. But do they work? And do you need them?

Water crystals are not necessary to grow healthy plants. The only case they can be beneficial is to help potted plants thrive indoors when it gets too hot and dry, especially during long summer days and not adequate watering is provided.

So precisely what are water-absorbing crystals, and how do you use them? How do you know if they are the right tool for your indoor plants? Read on to find out more.

Water Absorbing Crystals: What Are They?

Water crystals (also called water absorbing crystals) are mall granules made from absorbent polymers (a polymer is just a type of plastic). These crystals come in a variety of sizes, ranging from less than 1 millimeter to 4 millimeters in diameter. While the standard crystals used for gardening purposes are white, there are colored options available that serve decorative purposes as well.

When placed in contact with water, these crystals swell, absorbing several hundred times their weight in water. This makes them a useful addition to your indoor plant pots to greatly increase the water-holding capacity of the soil. Moreover, water-absorbing crystals are suitable for hydroponics. Hydroponics is a technique to grow plants only by water, without soil.

The actual amount of water that such crystals can hold depends whether you use them in the soil or alone (with water). Also, the concentration of some substances such as potassium, magnesium, and calcium in the water affect the water retention capability of the water-absorbent crystals.

For example, in pure distilled water, the crystals absorb around 400 times its weight. However, in potting mix, the crystals’ capacity to hold water is halved, with the crystals only absorbing around 100-200 times its weight.

Water Absorbing Crystals: Do They Work?

Water-absorbing crystals slowly release the water they are holding as the roots require them (yes, the roots actively absorb water from the crystals as they would from the soil). This condition creates a lasting “water storage” for your plants.

Experts from the University of Arizona and Washington State University have been studying the performance of such water-absorbing crystal for gardening purposes and have reported variable results.

Jeff Schalau, from the University of Arizona, here, shows that the type of soil and the amount of light impact the behavior of the water-absorbing crystals.

Hence, you have to be careful when reading online reviews or opinions. Are the reviews discussing indoor or outdoor applications? Indeed you need to understand that outdoor applications are way more challenging due to the impossibility to control temperature and watering (rain) compared to indoor ones.

When reading a review online, make sure to check if it is for outdoor or indoor applications, this might make a difference

In landscapes and outdoor containers, water crystals will have generally lower success due to different weather conditions. Jeff states that “for every success story, researchers have found situations where water-absorbing crystals have failed to function”.

However, when going through real-life experience after a chat with few friends (or friends of a friend), it is evident that those that struggle are most common for outdoor applications such as:

  • Plants in a very dry/hot environment: someone attempted to use such watering crystals in a very dry (desert-like) soil for outdoor plants. Unfortunately, the plants get dehydrated and died.

However, in more controlled environments, such as in indoor pots, are way more successful, as discussed here. Gardeners have been using these crystals in pots and containers with consistently positive results as a few gardeners I listened to claimed.

How To Use Water Absorbing Crystal For Plants

Any indoor plant can grow with water-absorbing crystals. However, they are best used for those plants, which have more significant watering requirements during hot weather such as basil, parsley, coriander, and rocket. This is because such plants have soft leaves and so more likely to wilt in the heat of long summer days. Hence, it is more important to make sure these plants have consistent access to moisture during hot, dry periods.

When using water-absorbing crystals for large areas, the general advice is to hydrate the crystals before mixing them into the soil. However, this is not necessary when using the crystals with your indoor plants. If you are planting new plant, there are just five simple steps:

  1. Fill your pot with potting mix (here the DIY recipe while here the best available in the market) suitable for indoor plants, leaving approximately 2 inches (5cm) at the top of the pot
  2. Mix through the required amount of crystals – as the crystals can vary across manufacturers, check the instructions to make sure you use the correct amount. As a rough guide, a 4 inch (10cm) pot only requires ½ teaspoon of crystals in the soil.
  3. Put the plant in the pot, leaving a 1 inch (2.5 cm) space at the top of the container to allow for the expansion of the crystals
  4. Water the soil thoroughly
  5. Wait a few hours, and water the soil again to ensure that the crystals holds the maximum amount of water.

However, you can also use the crystals in your existing indoor plant’s pots. In this case, you need to transplant your plant. Carefully lift the plant out of the pot and sprinkle the crystals at the bottom of the container. Place the plant back into the pot and water thoroughly. Some, also water the crystal before placing in the soil, should not make any significant difference. I think is more practical water them after, as easy to handle.

You need to remove the plant from its container in order to place the crystal at the bottom of it, close to the roots – One of my basil plants

This operation is necessary as placing the water crystals on top of the soil will be useless. Indeed, the roots extract the water from the crystals when they need it. If the crystals are on the surface of the soil (far from the roots) the water they hold will never be available to the plant.

Another way to place such crystals in existing plants, as suggested by a few gardeners in order to avoid a full transplant (and the potential stress, more here),  is to create holes in the soil deep enough to reach the root level. In each hole, you can place a scoop of crystals.

Water them and cover with the potting soil. I do not prefer such an approach as you might risk damaging the roots (if you do not stop digging early enough) and the crystal are not uniformly distributed all over the roots (that usually tends to use all the bottom are of the container).

You can also use the colored crystals as a decorative addition to plants planted in glass jars as discussed in this article.

The colored crystals can be placed on top of the rocks in the jar, making sure the roots of the plant contact the crystals so that they can access the water.

The crystals are incredibly long-lasting, and for most types of crystal on the market, you should not have to replace them in your pots for several years.

Water Absorbing Crystals: Problems?

The most significant problems with the use of water-absorbing crystals come from their overuse. Placing too many crystals into the soil can turn your pot into a “slimy mess” as discussed by these detailed gardener reviews.

The danger here is that the unnatural soil composition may damage your plants rather than help them. Also, if you do not get the proportions right (like using too many crystals), the expansion could disrupt and dislodge the plant severely damaging your plants.

While the product specifications usually state that the crystals are non-toxic and 100% biodegradable, some expressed their concern as the degrading effects of water-absorbing crystals on people are still unknown. However, there is no evidence of any effect on humans as professor Chalker-Scott from Washington State University stated “lack of documented information on the nature of degraded hydrogels makes it impossible to assess human or environmental effects.”.

Hence, the water-absorbing crystals can be considered safe as also used, without concern, in a large variety of other applications “including occupational use, garden products, and cosmetics”.

Where To Find Water Absorbing Crystals

You can purchase water-absorbing crystals from nursery stores and online retailers, including Amazon, Homedepot, Walmart, and eBay. They come in a variety of crystal sizes ranging from beads which are 1mm in diameter, to 4mm in diameter. I would recommend midsize crystals (approximately 2mm) are the best size for potted plants.

You can buy such crystals in several different options, from 100g package to bulk of several kilograms. One hundred grams (100g) costs approximately 3 EUR (around $3.30), and one kilogram is priced to 15 EUR ($16.50). Given that the crystals can last for several years, this cost is minimal for the benefit they can provide to your indoor plants.

To conclude, water-absorbing crystals are useful, and safe options to provide your indoor plants the water they need during hot and dry periods.

I do recommend them, especially if you cannot water your plants frequently or you leave in a location with long-lasting hot and dry summer days.

Using Moisture Crystals

Related Questions

Do water-absorbing crystals dissolve or jellify in the water? Water-absorbing crystal they expand, like a sponge. If in water in enough amount, the water will become like jelly.

Is it possible to replace soil with water-absorbing crystals? No, it is not possible because such crystal does not provide the nutrients, minerals, and right moist levels for plants.

Are water-absorbing crystals safe for insects? In case of ingestion, it should not cause any poisonous. However, they will expand in the digestive tract causing serious damage depending on the size of the insect. 

Further Readings

Useful info on how to transplant a plant, important to place the crystals in existing herbs – https://yourindoorherbs.com/how-to-make-supermarket-herbs-last-for-months/

Tips on how to maintain a basil plant, including watering (in case you do not want to use the water-absorbing crystals) –  https://yourindoorherbs.com/21-easy-tips-to-grow-massive-basil-indoor/

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