Also called hydro crystals or water gel, these tiny particles are the key to enjoying the health benefits of air filtering plants around the home without the worry of killing them due to improper watering.
This gardening tip also works well for potted plants that landscape the outdoor areas of your home. Vegetable and indoor herb gardens can benefit too. As a bonus, this strategy makes it easy to keep your plants properly watered while you are away from home for a few days, a week or even longer.
It is surprising to me that the garden attendants at some of the big box nurseries seem to have no idea about water crystals. The ones I’ve asked confuse them with perlite (the little white balls in potting mix) or decorative water beads.
Water Crystals for House Plants
Houseplants are an absolute must around the home to help clean and deodorize the air. NASA researchers suggest that the optimal air-filtering effect of house plants is achieved with multiple plants strategically placed around the home. One large plant can be used to cover a spacious area like the family room.
Even when just a few large plants are used, that’s potentially a lot of plants to water on a regular basis.
In addition to the chore of regular plant watering and the guesswork that is sometimes involved, the cost of buying plants quickly adds up. Add to that the high risk of shriveled plants in a short span of time for those who tend to lack much of a green thumb and the idea of artificial alternatives becomes quite attractive.
This is where water crystals come in …
Water Crystals Store and Release Water as Needed
These small, clear gel granules are made up of biodegradable polymers that have the ability to absorb up to 600-800 times their mass in water.
To use, all you have to do is mix a very small amount into the soil of each plant you wish to protect. These crystals help to preserve plant health by providing necessary moisture and reducing stress during times of drought. They protect from root rot during times of excessive rainfall or watering as well.
All your plants, whether potted, in the ground or in containers will go days and even weeks longer without watering!
Protection from both dryness and too much moisture is very powerful as these are the main threats to a homeowner’s living green investment.
How Many Hydro Crystals to Use per Plant?
There are two different types of water storing crystals on the market. The brand I’ve used for the past two years suggests approximately 1/8 teaspoon of water crystals for every inch in pot diameter. For example, a 4 inch pot would use 1/2 teaspoon of water crystals and an 8 inch pot would require 1 full teaspoon.
For larger pots, small amounts are still required. A one gallon pot would need 2 teaspoons of water crystals. A five gallon pot would require 2 tablespoons.
Mixing the water crystals evenly and deeply into the soil without disturbing the root structure is key. Otherwise, when the crystals swell with water, they can separate the soil and spill out of the container. This is similar to what happens during a frost heave which uplifts and expands water saturated soil when temperatures approach or dip below freezing.
To use water crystals with a newly potted plant, fill the container with potting soil leaving 2-3″ at the top. Mix the required amount of water crystals thoroughly into the soil. Pot the plant as usual and add additional plain potting soil leaving 1″ at the top of the container. Water thoroughly.
To add water crystals to an existing potted plant, make several holes in the soil evenly spaced around the plant. Add the required amount of water crystals evenly among the holes. Cover the holes with soil and water thoroughly.
To use water crystals in an open bed or garden, spread 1 tablespoon per square foot.
Are Water Crystals Safe?
In my experience, using water crystals definitely reduces the amount of watering required. This is especially true for outdoor plants.
Are the super absorbent polymers they are made from safe, however? Let’s take a more detailed look.
The typical polymers used to make water gel are divided into two categories: polyarcylamide and polyacrylate.
Polyacrylamide Water Crystals
Polyacrylamides (PAM) absorb about 300 – 400 times their own weight in water. They last between 5-7 years before biodegrading. While considered nontoxic when intact, there are some concerns that polyacrylamide water crystals mixed into soil may contaminate food plants with acrylamide, a known neurotoxin.
However, commercial polyacrylamide contains tiny residual amounts of acrylamide, usually less than 0.05%. A 1997 study at Kansas State University showed that environmental conditions on polyacrylamide can indeed trigger the release of acrylamide (1). However, a 1999 study by the Nalco Chemical Company did not replicate the results (2).
Polyacrylate Water Crystals
Given the conflicting research to date, I would suggest using water crystals made with polyacrylamides only for non-food based plants.
For vegetable gardens and trees producing edible fruits and seeds, polyacrylates (PAC), aka “green water crystals” would be advisable instead (get them here).
Green water crystals are able to hold 600-800 times their mass in water. Like polyacrylamides, they are considered nontoxic in intact form, but are more environmentally friendly when biodegrading. They first break down into ammonia salts and then nitrogen and carbon dioxide. This occurs within about 4 to 6 months. Polyacrylates are often sold with an environmentally friendly green label for this reason.
PAC water crystals are more expensive than PAMs, costing $10-12/pound versus $6-12/pound. This price difference is fairly insignificant considering how little is used, however. These green water crystals are the safer choice for your garden and fruit/seed bearing trees!
Have you tried using water crystals before to protect all the plants in and around your home and garden from too much rain or dryness? Did you find them helpful in conserving water and reducing landscape maintenance efforts?
Sarah, The Healthy Home Economist
The Healthy Home Economist holds a Master’s degree from the University of Pennsylvania. Mother to 3 healthy children, blogger, and best-selling author, she writes about the practical application of Traditional Diet and evidence-based wellness within the modern household. Her work has been featured by USA Today, The New York Times, National Review, ABC, NBC, and many others.