Hydrating Gel

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Janet Ibbotson

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Hydrating Gel
« on: November 26, 2012, 12:16:38 PM »
In the UK I sometimes use sachets of hydrating gel in pots to assist with water retention.  Other than cost, is there a reason why this gel shouldn't be used to help the ground to retain water here in the Mediterranean?  Does anyone have any experience of using gel?
Janet Ibbotson
MGS Member currently based in Skopelos, Greece but also gardens in Norfolk

David Bracey

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Re: Hydrating Gel
« Reply #1 on: November 26, 2012, 04:07:54 PM »
Here is a report which I think was only partially published in TMG.  Unfortuantely due to lack of interest at all levels the work of the Scientific Committee was abandoned.


                        The Scientific Committee
During the early 1960’s the U.S. Dept. of Agriculture (USDA) was engaged on the development of materials to improve water conservation in soils.  Prior to this time water absorbing materials were based upon cellulosic products, these having a water holding capacity up to 20 times their weight.
The initial materials, produced by grafting acrylonitrile polymers onto starch based molecules, were found to be capable of holding around 400 times their weight of water. This technology was released by the USDA to several American companies for further development; Japanese companies were, however, excluded.  Not withstanding, the latter embarked upon their own developments encompassing a much wider range of polymer forming materials. Over the years the technology has advanced so that there is little, if any, of the initial starch-grafted polymer in use.  
Curiously the first commercial products, developed in the 1970’s, were not used to improve water conservation in soils but in hygienic products such as, sanitary napkins and adult incontinence products; the natural extension of this application being their use in babies disposable nappies which appeared on the European market in the early 1980’s.
Super Absorbent Polymers (SAP`s) intended for soil modification tend to be cross-linked acrylic-acrylamide co-polymers containing potassium cations. Those used in disposable hygienic products are based upon cross-linked acrylic homo-polymers containing sodium cations.
 The Scientific Committee decided to test one of these SAP`s under Mediterranean conditions at three locations in the Languedoc region of France.  The same protocol was used throughout.
The SAP tested is sold under the name of “Water Magic” water retaining crystals via DIY stores and marketed by “Botanica/Nortene” a Division of Solu Garden Leisure Ltd.  Botanica is a registered TM.  This product is stated to belong to the polyacrylamide gel class of SAP’s.  It is a small solid cystal and easy to handle and mix. Prior to use the SAP was mixed, according to the suppliers instructions, into a general purpose potting/seed compost, NFU44-55.
Two litre plastic and terracotta pots were filled with the compost, alone and containing the SAP and planted with four Vicia bean seeds (variety “Feuillance”) which had been soaked in water for 24 hours to encourage quick germination. Each pot was replicated four times. Pots were placed outdoors and watered with tap water.
On average the pots received a minimum of 5-8 hours of direct sunlight with shade  temperatures rising to +/-23°C° and falling to +/-3°C. Over the trial period the plant pots were watered as required. Daily records of rain and watering were made.
After six weeks the bean plants were removed from the pots, the roots washed, dried and the sixteen plants, roots and shoots from each treatment weighed.

Results from the three locations are listed below:

Location 1 Carcasonne

plastic pots, without SAP         plastic pots, with SAP       

ave. plant wt.   64.1            ave. plant wt.    60.8 gm
ave. root wt.     22.3            ave. root wt.   29.8 gm
ave. shoot wt.    40.8            ave. shoot wt.   31.0 gm                   
terracotta pots, without SAP         terracotta pots, with SAP

ave plant wt   31.2 gm.         ave. plant wt.    69.6 gm         
ave.root wt.   16.3 gm         ave. root wt.    38.8 gm
ave. shoot wt.    14.9 gm         ave. shoot wt.   30.8 gm
The results show that terracotta plus SAP produced the sturdiest plants and that plastic pots plus SAP generally produced the second best results.

Location 2  Beziers

plastic pots, without SAP         plastic pots, with SAP
ave. plant wt.   30.3 gm         ave plant wt.  23.6 gm
ave root wt.     15.9 gm               ave root wt.   11.8 g
ave shoot wt.   15.0 gm                ave shoot wt. 12.9 gm

terracotta pots, without SAP         terracotta pots, with SAP

ave plant wt.     26.7 gm         ave plant wt. 29.3 gm
ave root wt.    15.0 gm                 ave root wt.   16.0 gm      
ave shoot wt.   12.7 gm                ave shoot wt. 14.7 gm

Total volume of water added during the 6 week trial:

Plastic pots and no SAP 2250mls, plastic pots with SAP 2050 ml
Terracotta pots and no SAP 3150 ml, terracotta pots with SAP 3200 ml.
The only firm conclusion is that terracotta pots consume about 50% more water than plastic pots.

Location 3 Uzes

All pots were watered 8 times and the terracotta pots were watered 9times

plastic pots, without SAP         plastic pots, with SAP

ave. plant wt    44.7gm         ave. plant wt.    51.4 gm
ave. root wt.   31.6gm                    ave. root wt.    37.3 gm
ave. shoot wt.  13.0gm                 ave. shoot wt.  14.0gm

terracotta pots, without SAP         terracotta pots, with SAP

ave plant wt.   46.2 gm             ave plant wt.  56.1 gm
ave. root wt.   36.2 gm                  ave root wt.   44.8 gm
ave. shoot wt. 10.0 gm                  ave shoot wt. 11.2 gm
Results were superior with SAP cf no-SAP as far as plant, root and shoot weights are concerned.
Terracotta pots on the hole produced heavier (better?) plants although shoot weight was reduced compared to the plastic pots.

Conclusions. Results from this experiment are inconclusive. The effects of the addition of Super Absorbent Polymers to compost could not be determined accurately.

However at location 1 terracotta pots with SAP, at location 2 terracotta with SAP and at location 3 both plastic and terracotta pots with SAP gave superior results in terms of plant, root and shoot weight compared to similar treatmets without SAP.

 Plastic pots require less watering than terracotta pots
« Last Edit: December 05, 2012, 05:26:28 PM by Alisdair »
MGS member.

 I have gardened in sub-tropical Florida, maritime UK, continental Europe and the Mediterranean basin, France. Of the 4 I have found that the most difficult climate for gardening is the latter.


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Re: Hydrating Gel
« Reply #2 on: November 26, 2012, 04:18:46 PM »
Janet, I have used it here in Crete.
I put it under plants, when planting.
I have only used it with those plants that I know need extra moisture.
If I am honest, I cannot say that I have noticed any difference.
I hand water my garden, once a fortnight in summer and when the next watering is due it is always the usual suspects that are flagging. This is the same, whether they have water retaining crystals added or not.
I haven't added it to those plants in pots, as they get watered more often. Also, I don't want to make the compost in the pots, too soggy in winter.
In the open garden, it doesn't seem to cause a sump in winter, but then it doesn't seem to make any difference in summer either.
Daisy :)
Amateur gardener, who has gardened in Surrey and Cornwall, England, but now has a tiny garden facing north west, near the coast in north east Crete. It is 300 meters above sea level. On a steep learning curve!!! Member of both MGS and RHS



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Re: Hydrating Gel
« Reply #3 on: December 03, 2012, 10:55:40 AM »
Hobbygardener (MGS member) with a rooftop garden in Basel and a garden on heavy clay with sand 600m from seaside in Costa Blanca South (precipitation 300mm), learning to garden waterwise


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Re: Hydrating Gel
« Reply #4 on: August 10, 2013, 01:14:55 PM »
Just a note to say I tried this again this year on my Crocosmia Lucifer.
I planted the bulbs in two groups, last year in February. They all grew, but only to about a third of their normal height. None of them flowered.
I wasn't sure if this due to insufficient water, or the fact that they had been planted late.
This year in late winter, I raked in a handful of water retaining granules around one of the groups. These grew up to their normal size this summer and they all flowered.
The other group that I had left alone stayed small and again did not flower.
Daisy :)
july 2013 037 by Daisyincrete, on Flickr
Amateur gardener, who has gardened in Surrey and Cornwall, England, but now has a tiny garden facing north west, near the coast in north east Crete. It is 300 meters above sea level. On a steep learning curve!!! Member of both MGS and RHS

Trevor Australis

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Re: Hydrating Gel
« Reply #5 on: August 11, 2013, 01:13:05 AM »
I have used two forms - a powder that is mixed with water and then watered into the soil around water dependent plants, and squidgy gel globules which are simply mixed with the soil prior to planting. Both kinds certainly hold water and retain it but do they give it up to needy plants? Well, that is a big question mark for me. Daisy's experience suggests that it may. I do worry about the stuff in both forms. First, it gets really sodden during winter and I worry plants being grown with it in the soil may drown or rot. Second, I haven't seen any information about how long it lasts and what happens when it breaks down, what it breaks down into, what happens to the soil, what impacts does this have on plants? It all seems to have too many un-answered questions for me to use it widely. tn
M Land. Arch., B. Sp. Ed. Teacher, traveller and usually climate compatible.

David Feix

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Re: Hydrating Gel
« Reply #6 on: April 08, 2014, 06:09:14 AM »
I hadn't been aware these hydrogels could break down into potentially toxic byproducts, but was already aware that common salts and fertilizer quickly degraded their water holding capacity.., making them virtually worthless for the purpose stated. Pity that the research stating these results doesn't seem to have counteracted the propaganda for their use.Quite similar to the inflated claims for spray-on frost protection products.
David Feix Landscape Design
Berkeley, California, USA