Crystals help retain water in soil

Dry water crystals (left) and the same amount after absorbing water (right).

My son graduates from high school this year. Seems like just yesterday we were taping diapers on him.

We tried cloth diapers, but disposables proved to be too convenient. They start out light as a feather but turn into 10-pound soggy shorts due to the magic of water gel polymers, sometimes referred to as water crystals.

One pound of water crystals can hold 50 pounds of water. Dry crystals look like coarse sand. Once they’re saturated, they look and feel more like slimy gelatin.

This disposable diaper technology is used in horticulture to extend water availability in the soil. Florists have used them in clear vases to extend the turgidity of cut flowers. Some water crystals are dyed to create colorful arrangements and to float candles.

Some potting soils pre-mix water crystals and readily advertise that on the bag. However, water crystals can be purchased separately and mixed into potting soil or used in the landscape.

Water crystals are helpful in potted plants, especially in the summer, when containers can dry out rapidly. The crystals absorb water and slowly release the moisture as the soil dries out.

Water crystals also can be applied to soil mixtures used for houseplants, but keep in mind, containers still can become root-bound to the point that water crystals have little effect. In this case, repotting is necessary.

Recently, we ran a trial in Trident Technical College’s horticulture program on the growth of snapdragons with various products, including humates, fertilizers and stimulants. We expected the water crystal treatment to improve drought resistance since many products claim reductions in irrigation by 50 percent.

Surprisingly, the water crystal treatment produced the best-looking flowers after eight weeks of growth. This likely was due to fewer soil moisture extremes. One experiment we’ll begin this summer is constructing a green wall with milk crates. The vertical orientation makes the soil more susceptible to drying out. We’ll mix only half of the containers with water crystals and record the results.

Water crystals have been used to amend flowerbeds and vegetable gardens where irrigation is limited. They also can be worked into the soil before laying sod.

I’m not convinced that top-dressing the crystals over the lawn is effective, especially since the crystals swell into slimy globs of gelatin. In this case, whatever moisture they retain is likely to evaporate into the air rather than reach the root zone.

Soil structure also has been reported to improve with the presence of water crystals. Uninhibited, water crystals have been reported to swell 100 times in volume. This expansion and contraction supposedly will open pore space for the soil to breathe.

Water crystals often are mixed with biological soil amendments to moderate moisture extremes, encourage adequate pore space and, finally, hold nutrients near the developing roots.

The lifespan of water crystals is not infinite. Most products will decompose into nontoxic byproducts after five to 10 years. Some water crystals products are potassium-based rather than sodium, claiming kinder byproducts during decomposition.

Despite the potential advantages of water crystals, nothing is a substitute for proper watering. Deep-rooted plants find additional water farther down in the soil profile. In fact, occasional dry periods stimulate root growth to seek out water. This is why frequent irrigation causes shallow-rooted plants: They don’t have to go find water. As a result, you create plants that are addicted to the irrigation system and have little ability to handle drought.

On the other hand, deep and infrequent irrigation can boost more durable root systems.

One last application of water crystal in the horticulture field has to do with evaporative cooling. Water crystals can be sewn into headbands, scarfs and jackets to keep the horticulturist cooler during the heat. As water evaporates, it uses a small amount of energy in the form of heat, similar to the effect of sweating. These products can be effective for hours. Additional ones can be stored on ice to keep them fully hydrated and cool.

Tony Bertauski is a horticulture instructor at Trident Technical College. To give feedback, email him at