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I want to observe root development of plants for a hobby home experiment. I need transparent soil for this purpose.

I asked some local gardening stores for it, but they said that they don't sell such a thing. Is there any way which I can make it myself at home with as simple materials as possible?

Requirements:

  • It must be very transparent if not completely.
  • It mustn't contain any ingredients that would harm plant roots.
  • It must be able to carry oxygen from air to the roots of the plant.
  • It must be able to hold water in it, and supply it to the roots.
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Why did they emigrate my question to this domain? This was a chemistry question. I'm not looking for a gardening product, because it is not sold in my area. I'm looking for a chemical solution to produce transparent soil. –  hkBattousai Aug 22 '12 at 14:07
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Unfortunately that is off topic for chemistry. It is on topic here. We handle pretty much any plant question you can ask. –  wax eagle Aug 22 '12 at 17:53
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I could be wrong, but my understanding of the "normal" way to study root development would be to grow a number of plants in whatever growing medium you want (e.g. in the field, in pots with manufactured potting soil, etc), and then carefully dig them up and observe the roots. By growing many plants, you can dig up batches at whatever intervals you want to study. For example, you might grow 100 plants and then dig up and measure/study the roots of 10 plants at 1-week intervals for 10 weeks. –  bstpierre Aug 22 '12 at 19:49
    
@bstpierre This wasn't supposed to be a scientific experiment. I just want to make an interesting graphic experiment to show my friends. I'm not a biologist. –  hkBattousai Aug 22 '12 at 19:58
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Maybe a plant would grow in gelatin with plant nutrients added to the mixture? –  Spießbürger Aug 25 '12 at 19:00
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migrated from chemistry.stackexchange.com Aug 22 '12 at 13:46

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5 Answers

Kevinsky might have the right idea. However, the Nafion polymer referred to in that PLOS article might be overkill. It's priced at ~$5.00/gram which might be more than someone would be likely to want to spend for an interesting graphic experiment to show their friends (and this is without even going into the additional processing to make it more soil-like as described in the journal article cited).

While having something closely resembling soil is useful for researchers interested in knowing what happens in real soil, plants do not need such a good soil simulacrum to actually grow well; and, as Ben Norris has pointed out, many will even grow very well without any soil or support of any kind at all.

If it were me, I, like permeakra, would try using something like polyacrylamide hydrogel beads which will be orders of magnitude cheaper than the Nafion beads. I would probably also do some sort of processing to achieve a smaller particle size than the sizes you are likely to get easily (the researchers in the article which Kevinsky cited did this as well).

This won't necessarily result in a fully viewable, transparent growth medium, though. To achieve that you will need to fill your growth container to the top with the irrigating solution to eliminate all air spaces. The similar refractive index will make the fully hydrated hydrogel particles nearly invisible (the researchers in the article which Kevinsky cited further adjusted the refractive index of the solution using sorbitol or percoll to better match the refractive index of the beads they used but this will probably be unnecessary with the cheaper hydrogel beads and for this application).

Having the growth medium waterlogged may work with some plants but not with others (because roots generally need oxygen). In the latter case I can think of two solutions to deal with this issue:

  • Constructing a hydroponic circulating system which aerates your nutrient solution (so the water level is always high but there's enough circulation to prevent a hypoxic root environment).
  • Living with the fact that the medium is not transparent and keeping it in a container with a drain hole. One could plug the drain hole and add water whenever one wished to visualize the roots (which is what the researchers in the article cited by Kevinski actually did).

Also, you might be interested in having a mechanism in place set to block light to the root area when not viewing the roots since it may affect some plant roots and, as kevinsky pointed out, will promote undesired algal growth.

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Transparent glass beads or marbles in a transparent glass would do the job. Many plants will do quite well in water. The beads are for mechanical support for the stem.

You might find algae will become a problem as it too will grow in water. Flushing with fresh water on a regular basis and keeping the container out high light will control this.

Edit This recently published study covers exactly what you are asking for. The researchers used

Nafion, the building block of transparent soil, is a transparent ionomer (synthetic polymer with ionic properties) that is physically and chemically adaptable. Nafion particle size distribution has been manipulated by freezer milling (250–1600 µm).

This product appears to be available at chemical supply houses but might require some processing. It is described as

suitable for growing and imaging the roots of various plant species, including alfalfa, barley, maize (data not shown), tobacco, lettuce and thale cress (Arabidopsis), and imaging at the whole root level can be achieved using OPT (Fig. 2A). Transparent soil provides images with low levels of noise and opens avenues for automated analyses of genetic screens.

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I have had a lot of success transferring my indoor plants to hydroculture. Bamboo, aechemia fasciata (silver vase or urn plant), aloe vera, hippeastrum (commonly sold as amaryllis), and araucaria heterophylla (norfolk pine) have all thrived in plain water, sometimes with rocks or marbles added for support, and provide a very nice view of the roots. I have, however, noticed that the water roots look slightly different than the soil roots (which die off eventually after being transferred to water, being replaced by the roots adapted to the water environment), however, the growth pattern of the roots seems unchanged.

As mentioned above, the water needs some circulation to keep it oxygenated, both for the plants' health and to prevent stagnation of the water. For very thirsty plants, this is achieved simply by topping up the water level with a watering can when it gets low, with plants that do not drink as much, I occasionally need to dump the old water before adding more.

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There's a product call gel 2 root which is a clear cup with a clear gel in it that you can use to root cuttings of plants. I'm not sure how it would work if you tried to start seeds in it and keep the plants growing, but for cutting this would be a good way to see the root structure as the plant grows.

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You can search for polyvinyl alcohol granules. They often have pigment mixed in, but polymer itself does not have any color, is transparent and keeps big amount of water. You also can consider avoiding usage of soil at all as some plants grows well in pure water without soil.

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Probably the best way to go would be to not use soil at all, as permeakra suggests. Hydroponics is a well-developed means of plant culture. –  Ben Norris Aug 21 '12 at 21:04
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