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, retrieve the absorbent crystals inside and add these crystals (hydrogels) to the potting mix of your houseplants. And it seems to make sense: after all, hydrogels are said to absorb 500 times their weight in water. Thus, the crystals ought to absorb water and release it slowly, keeping your plants moist longer. The video claims 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 compelling and enthusiastic, the video seems to show you exactly what to do… so far, so good! But there’s a catch: it simply doesn’t work!
You should know hydrogels absorb water very well, but are not so good at releasing it. After all, disposable diapers are designed to absorb liquids but not with the idea that you’ll then expect them to dry out for future use. Thus, a plant treated with these crystals will have approximately the same watering needs as a plant growing 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 you compare ordinary potting soils and the same soils with added hydrogel crystals. In fact, in some tests, the plants growing in hydrogel mixes dried out more quickly than those without the mix. (The difference was minor, but still!)
I tried a very small-scale experiment with hydrogels about 20 years old, when hydrogels first came on the market. Only two plants, so it wasn’t a thorough test. Still, I saw no difference in either the amount of water needed for the two plants nor any difference at all in frequency. I haven’t used hydrogels since!
Of course, that may be a mistake. There are modern hydrogels designed for horticultural use that are likely better for plant culture then chopped up diapers. Even so, though, if you read scientific reports on the subject, the results are not very conclusive. It would appear hydrogels work (a bit) under some circumstances and not at all in others.They seem to operate best when used in the ground (and not so well in pots) using very drought sensitive plants. Plus there are questions about what happens to them when they degrade (they don’t last forever).
My conclusion? Keep diapers for baby and use normal potting soil for your houseplants…
But what a minute! Just because crystals harvested from diapers are essentially useless as a watering agent for container plants doesn’t mean they have no useful functions. In the video, you’re shown how to use hydrogels to keep cut flowers moist and that will work. Not mentioned is the fact you can root cuttings in them as well, although eventually you’ll have to move them to real soil. And you can color hydrogel crystals as per the video with food dyes, turning them 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 into containers with no drainage holes (not very good horticulture!), a strange tip about mixing seeds with a hydrogel/potting mix blend (you’d get the same results in potting mix alone… and what a waste of seeds too!), and a few others.
The most surreal point in the video is when it recommends not adding food coloring to the crystals in potting soil so “your plants won’t turn funny colors as they grow”. Well, actually, you can pour all the food coloring you want into soil with or without hydrogels and the dye simply won’t change the plant’s color. Plant roots cannot absorb food coloring directly, they must wait until it is broken down into simpler molecules, and by that stage, the color has been lost. So your plant will keep its original color regardless of any color added.
That said, you can do a neat little experiment by coloring flowers, not plants. If you put cut flowers in hydrogel or water stained with food coloring, the flower will take up the food color. That’s because the colored water passes directly into the flower stalk where vascular tissues carry it to the flower’s petals: there are no roots to act as filters. This phenomenon is observed more easily with white flowers, as they have no pigments to mask the dye. This technique is widely used in the floral industry: you’ll find plenty of dyed flowers in almost any florist shop.
So, a fun video to watch and very thought-provoking, but somebody forgot to do their homework!