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Watering Houseplants With Membrane Osmosis

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by Chris_Moran on July 14, 2005 03:49 AM
Hi, Posting from Scotland, UK. I have kept an african violet for 4.5 years during which time it has had 10 consecutive flowerings and is >12inches in diameter. See picture below.


At the begining I was a complete novice and had never owned an african violet. However, my first plant has been described as "almost show standard" by the UK Saintpaulia and Houseplant Society. I believe that the key to my success is the way in which I have watered the plant.

I am a polymer technologist with a speciality in developing hydrogels for medical, biomaterials, membrane and sensor applications. I developed a plant watering system that uses hydrogel membrane technology to deliver water by osmosis or diffusion to plants. Water passes from an external reservoir through a special hydrogel membrane into a plant container. The water entering the container dissolves nutrients and salts from the soil or growing media. This soil solution causes an osmotic potential difference to develop across the membrane separating the reservoir and the plant container. As the plant draws water through its root system, more water is drawn through the membrane from the reservoir. All I need to do is make sure that the reservoir is kept filled with water. I add commercial nutrient products every few weeks to the plant container.

Over the last 4.5 years I have recorded how often I refill my african violet's reservoir. Generally 300ml of water can last 20 - 30 days which I think is really surprising for a plant of >12 inches diameter. However, just before flowering the plant uses 300ml of water every 4 or 5 days. I can now predict when the plant is about to flower based on the increase in water uptake in the weeks before flowering. I have also noticed that the plant has 2 flowerings per season and that these flowerings are relatively close together with a longer period between seasons. I re-pot about once every 18 months.

I am amazed at the success that I have had and the plant is now like a member of the family which I would sorely miss if it died. I know that enthusiasts will have kept plants for much longer and will water their plants expertly through experience and knowledge. I'm delighted with what I have achieved but also fascinated at how little water the plant seems to need once it established itself on my watering system. I know that most people will not want to record every time they water their plants but this kind of data may be useful to some. I feel my plant is performing better because it is effectively controlling its own watering and is not subject to a feast and famine regime. I now have several african violets around the house and many other common houseplants like begonias, chrysanthemums, poinsettia, gerbera, orchids etc, etc - all watered using my membrane osmosis watering system. Chris
by hisgal2 on July 14, 2005 03:57 AM
Hi Chris,
welcome to the forum. Your plant is gorgeous. My mom has an african violet that drinks it's water through a string as if it were a straw. [Smile]

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by tkhooper on July 14, 2005 09:22 PM
So Chris,

Tell me more. Much much more. What exactly is hydrogel? and how do you get it from the resevoir to the membrane and then to the soil. Can you take a picture of the setup say before you put a plant in a container that is going to be watered this way. And why do you feel that it is different than just regular bottom watering? Have your tried different systems say starting with seeds of the same plant to see how it differs? I'm very curious. I wish I could invent good things like that. Mostly I just jury-rig with anything handy with very mixed results.
by Chris_Moran on July 15, 2005 10:28 PM
Jenn - Capillary wicking seems to be very popular in the US for African violets - and many get great results. My system actually prevents capillary wicking flow from the reservoir but instead uses osmosis or diffusion. Some wicking systems can deliver too much water since the water is driven to fill all available capillaries continuously. You can also get backflow of the dirty brown pigments and other material which can contaminate the reservoir. My gel membrane prevents this and will also prevent harmfull bacteria from entering the pots.

tkhooper - hydrogel is a generic term for the many different (chemically and structurally) natural and synthetic materials that absorb and swell with water without dissolving i.e. the water becomes part of the molecular structure which differentiates them from sponges and the like where the water is held inside pores and capillaries. Common examples of hydrogels are soft contact lenses, 'cool' dressings for wounds and alleviating headaches, the stuff that is inside babies' diapers which is the same as the typical water holding\releasing crystals used for looking after houseplants.

My system is different in that it prevents capillary wicking and hydraulic (pressure) flow of water into the pot but instead uses membrane diffusion or osmosis. The driving force for this is the concentration differences between the pot side (higher salt\lower water) and the reservoir side (lower salt\higher water). Water and salts move through the membrane to balance the concentrations either side; the plant essentially draws water through the gel membrane.

Here is a schematic of my invention

[flat-based pot sits on top of special hydrogel membrane sits on top of fabric (to allow water underneath the membrane to maximise surface area]

I can report on some comparative trials with capillary matting trays, feast and famine, and expert watering.

Hope this helps some.
by JV on July 17, 2005 04:50 AM
Chris this system looks like it would fit the bill here in Texas and the southwest where we have more water restrictions then our Northern friends. Also I have to leave my plants sometimes two to three weeks ata time. I am very interested in your system. We are under a water ban now $500.00fine to water by sprinkler from 10:00am until 6:00 pm also in my home state of New Mexico would be handy because of lack of water (this is desert country )that way we could setup our plants like I have my animal lights on a timer of sorts and be better able to produce bloom which in turn better seed pods. Please post more on this topic. I am very interested in trying it. I always like trying new ideas anyway.

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by newlife on July 18, 2005 06:58 AM
Ever thought about marketing and selling your system? Dry climates would love it.
by Chris_Moran on July 21, 2005 06:25 PM
Here's a pic of a typical basil that I can grow using my system.


I am hoping to make contacts with North American distributors, retailers and selling agents but I'm not really sure where to start - it's a big place!


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