There is a video circulating these days (How Can Diapers Help Your Plants Grow?) that several people have sent me. It suggests that you can cut open a disposable diaper, get out the absorbent crystals inside, and add those crystals (hydrogels) to your houseplants’ potting mix. And it seems to make sense: after all, hydrogels are supposed to absorb 500 times their weight in water. So the crystals are supposed to absorb water and release it slowly, keeping your plants moist longer. The video claims that it cuts your watering needs in half… and who doesn’t want great results with less effort? Plus, the video seems very professional, the narrator is convincing and enthusiastic, the video seems to show you exactly what to do…. so far, so good! But there’s a catch: it just doesn’t work!
You should know that hydrogels are very good at absorbing water, but not so good at releasing it. After all, disposable diapers are designed to absorb liquids, but not with the idea that they will then dry out for later use. So a plant treated with these crystals will have about the same watering needs as a plant grown in a more traditional growing mix. This is confirmed by test after test: there is little to no difference in the frequency of watering when comparing normal potting soil and the same soil with hydrogel crystals added. In fact, in some tests, plants growing in hydrogel mixes dried out faster than those without the mix. (The difference was small, but still!).
I did a very small scale experiment with hydrogels that was about 20 years old when hydrogels first came on the market. There were only two plants, so it wasn’t a thorough test. Yet, I could not detect any difference in the amount of water needed for the two plants, nor any difference in frequency. I have not used hydrogels since!
Of course, this may be a mistake. There are modern hydrogels for horticulture that are probably better for plant culture than cut-up diapers. However, if you read scientific reports on the subject, the results are not very conclusive. It seems that hydrogels work (a little) under some circumstances and not at all under others. They seem to work best when used in soil (and not so well in pots) with very drought sensitive plants. Also, there are questions about what happens to them when they degrade (they don’t last forever).
My conclusion? Keep diapers for the baby and use regular potting soil for your houseplants….
But what the heck! Just because diaper-derived crystals are basically useless as a watering agent for potted plants doesn’t mean they don’t have useful functions. The video shows you how to use hydrogels to keep cut flowers moist, and it works. Left unmentioned is the fact that you can also root cuttings in them, although you will eventually need to transplant them into real soil. And you can dye hydrogel crystals with food coloring, as in the video, so they take on the color of your choice. You’ve probably seen hydrogels, often in the form of gelatinous beads, used this way in plant shows and county fairs, but crystals extracted from diapers will give a similar result.
There are a few other inconsistencies in the video; you see plants potted in containers without drainage holes (not good gardening!), a strange tip about mixing seeds with a hydrogel/soil mix (you’d get the same results with a pure soil mix…. and what a waste of seeds!), and a few others.
The most surreal point in the video is the recommendation not to add food coloring to the crystals in the potting soil so that “your plants don’t turn funny colors when they grow.” Well, actually, you can add as much food coloring to the soil as you want, with or without hydrogel, and the dye simply won’t change the color of the plant. The plant roots can’t absorb the food coloring directly, they have to wait for it to break down into simpler molecules, and at that stage the color is already lost. So your plant will keep its original color no matter what color is added.
However, you can do a nice little experiment by coloring flowers, not plants. When you place cut flowers in hydrogel or water dyed with food coloring, the flower absorbs the food coloring. This is because the colored water goes directly into the flower stem, where it is transported through the vascular tissue to the petals: There are no roots that serve as filters. This phenomenon is easier to observe in white flowers, as they have no pigments to mask the dye. This technique is widely used in the flower industry: You can find many colored flowers in almost every flower store.