Those of us involved in gardening for a while are likely familiar with water-absorbing polymers. They’re the crystals used in diapers, and in many plant nurseries for liquid absorption and retention. Depending on the source you read, they can hold from 10 to 500 times their weight in water and are non-toxic: they look like rock salt when dry and like crystal clear gelatin when they have absorbed water. I’ve been aware of these for some time, but only recently started using them due to the drought here in the west.
There are some pretty strong claims made for these crystals – many claims that they help to conserve water because they release it slowly to the plant as needed. This, it turns out, is untrue. According to a comparison done by University of CA Agriculture¹ while water is released slowly to the plant, the crystals did not reduce water use overall. Even though the water was released more slowly to the plant, a heavier than normal watering was needed when the plant was watered. And in very small pots (1 and 3 quarts), the plant’s growth and water retention “were not particularly affected”, but in 6 quart size pots “maximum water retention was significantly higher for the 4 lb/yd³ polymer treatment than for the other treatments, and the time from watering to wilt progressively increased from 6.1 to 7.4 days for the 0, 1, 2 and 4-lb/yd3 treatments.”
This comparison was done using two-week old marigold plants; none were seeds started in the polymer-infused mix. I have started all my seed this year using either potting mix and polymer or polymer alone (for hydroponic starts). What I have found is that I have a higher and quicker germination rate in the potting mix polymer while it seems to have been indifferent at best using the polymer alone (possibly due to the roots getting light, as I made no real effort to shield the starts from it). I do have some basil which is coming up in the polymer now, but it seems less robust than starts done in hydroponics previously – but I have not added any nutrient to the water for these starts in addition to making no effort to shield roots from light, so this is perhaps not a fair comparison.
What I have noticed is that I am watering the starts less often. Anyone who does a large number of starts knows what this means. Keeping seeds and seedlings watered can be very time-consuming and frustrating: how to give enough but not too much water so the seeds/seedlings are neither drowned nor dried out. But what are the biggest change I’ve seen? I have seen absolutely no damping off on a single potting soil seedling as yet. This has not been my experience in the past. By now I would have started quite a few seeds over: I have not had any failures except with one seed which I found out I should have started outdoors to begin with (non-germination, not dampening off).
I only planted one seed in most cases, as I had visions of tossing large numbers of starts (basil was one exception where I planted several seeds of each type in the polymer alone, excepting Boxwood Basil, which is coming up nicely in the potting soil/polymer mix). I planted one each of a wide variety of peppers and tomatoes, figuring that what made it, made it, and I would likely be replanting most anyway. Now I have a pretty good array of plants for the garden: at last count 60 different plants, some of which I have never been able to even germinate in the past (lavender, oregano, thyme). Considering the seed I used for the lavender and some of the thyme was 5+ years old (and something I just threw in thinking, “Why not?”), I was impressed.
The great thing about not worrying about over-watering and damping off – if I water a little too much, the crystals simply absorb the excess and only release it as the seed or plant needs it. I haven’t even bothered to put holes in the bottom of the cups for the starts. No more “killing them with kindness,” or because something comes up and I simply can’t get back to water them soon enough. You do still have to water – and I still check every day, but often have gotten away with watering every other day or even two days when first starting seed (we all know as seeds germinate seedlings take more water).
These crystals are also reusable: they will last up to 7 years even sown in your garden. They swell up to the size of a quarter, so should be easy to remove from used potting soil, should you choose to, simply by saturating the soil with water and sorting them out.
And I do think they will help conserve water: while the comparison mentioned above by UCA Ag shows it won’t save water right away, think of all the water wasted on starts that die off through over or under watering. How much water do you waste by tossing dead starts and plants? Answer: every bit of it you ever used on those starts or plants is wasted. And here in my area, we have been in a drought for some years. We are allowed to water only twice a week. Anything that can help hold water in the soil longer between waterings will help preserve a garden and avoid the total waste of water that losing the garden would result in.
And the polymers themselves are very cost effective: I paid about 20 dollars (that’s including shipping) for a two pound bag of what looks very much like rock salt. After doing 70-80 starts, potting a half dozen strawberries, a half dozen small plants, a large berry plant, two medium fruiting plants, two very large containers for onions and my entire 200 sq ft garden plot (see note) with them, I really can’t even tell I made a dent in the bag. I may have used a third of a cup, but I doubt it.
Some tips on using polymers: I mix them with water before mixing them with my potting mix. Otherwise, you can easily return to your starts to find the polymer has expanded so much it has pushed most of your potting mix right out of the container. Don’t pour them down the sink. If you do happen to spill some down the drain, it is recommended that you add table salt and flush with hot water. Don’t let pets or children eat them, for obvious reasons. Do not take them internally².
Don’t top dress plants with these polymers: mix the water-activated polymers right into your soils so the water will be available to plants’ roots. You can dip transplant roots in the polymer gel before planting, and coat the roots of bare root plants to preserve for travel or shipping³.
I set some bare root plants that arrived before I had time to plant them into a container filled with the gel and simply covered the top of the container with a small scrap of landscape material to block light from the roots, then left the plants under grow lights. By the time I got around to planting them, the plants had developed some beautiful little white roots down into the polymer gel, and they never dried out. I checked every two days and added water if needed until I found time to plant them. The plants flourished and never experienced the droop that tells us we need to water them, nor the rotting of roots that comes when we overdo it.
When it came time to put them in containers, instead of the ‘good watering in’ we’re advised to give plants, I simply mixed the polymer throughout the potting mix, keeping it heaviest at the bottom of the container, to encourage roots to grow deep. This kept the mix light and kept the potting mix from getting heavy and soggy. I didn’t water the pots in: in our humid climate, I have often had problems with the ‘watering in’ of container plants where the pots would not dry out fast enough to keep new roots from rotting. Both plants showed no detectable sign of transplant shock and are doing well.
The possibilities of this medium in gardening are only beginning to be explored. I have no doubt this will soon become as necessary to gardening as the best soil amendments. Hopefully this article has suggested some uses to make your gardening easier, cheaper, less of a strain on natural resources, and more productive.
Note: Some gardeners have noted that, in sandy soils, due to the expansion and retraction of the crystals, they eventually manage to work their way to the top of the soil in a garden bed. It has been suggested that digging the crystals in deeper and placing the crystals deep in a planting hole may help with this. Others have reported having no problem with the crystals resurfacing in other types of soil. With my own container plants, I have noticed the potting mix seems to stay much lighter for much longer, and I never water deeply, only lightly to maintain this. I can do this with little worry because the pots don’t dry out as quickly. I have had no problem with the polymer resurfacing as of yet.
Thanks to L.L. McBride for participating in the [Grow] Network Writing Contest. We have over $1,500 in prizes lined up for the current writing contest, with more to come. Here is a list of the current pot of prizes:
– A 21.5 quart pressure canner from All American, a $380 value
– A Survival Still emergency water purification still, a $279 value
– 1 year of free membership in the [Grow] Network Core Community, a $240 value
– A copy of The Summer of Survival Complete Collection from Life Changes Be Ready, a $127 value
– 2 copies of the complete Home Grown Food Summit, valued at $67 each
– 3 free 3 month memberships in the [Grow] Network Core Community, valued at $60 each
– The complete 2014 Grow Your Own Food Summit interview series, a $47 value
– 4 copies of the Grow Your Own Groceries DVD video set, valued at $42 each
– A Bug Out Seed Kit from the Sustainable Seed Company, a $40 value
– 4 copies of the Alternatives To Dentists DVD video, valued at $32 each