I really don't know, just my talking out loud.

For more info on crystals, check out a book by Scott Cunningham, I believe its called "Encyclopedia of crystals, gems, and metals." Or something like that! You can find it in the "new age" section.

if you don't mind a little mumbo-jumbo from the local hippy...

blah, blah crystaline structure, blah blah vibrational frequency, blah blah 'secret life of plants' blah color enhancing light (light, sound, both vibrations, different levels of the same thing)

personal opinion? some plants do better because they like the attention, some do better because they like 'dressing up' some do better because the crystal refracts a bit more light to shaded leaves....

theoretically:
a hematite at the bottom of the pot encourages rooting

quartz is always an energizer,
amythest a 'cleanser'
and carnelian encourages growth.

malachite is toxic to both plants and people ( copper something is the main coloring agent) by the way- though the cacti don't seem to mind it as much (no water, no leaching toxins, maybe?)

Water will run off stones to reach the soil, but the stone helps prevent evaporation by minimizing the amount of exposed soil.

Earthworms and other such beneficial critters will be attracted to the area due to the extra moisture.

Stones absorb heat during the day and release it at night, which may help some plants, especially in early spring and late fall.

Anywhere there's a stone, there will not be a weed competing for nutrients and water. And, unlike organic mulches, stones don't need replacement every year or so.

There is also a field of the study of movements (vibrations?) and plant growth.

In a physics sense, everything is just vibrating. A tree is just a semi cohesive grouping of vibrating energy. As is a cell, an organ, a bone, skin, your body. Our perception of things relates a lot to the 'rate' of vibration, or the frequency, however you want to put it. Everything we experience is 'compared to' or filtered by our body. So our body has a certain range of frequencies that it can/will perceive. Stuff outside that, we're oblivious to.

So at one rate of vibration energy is an X Ray... it comes down in speed, and eventually is seen as visible light, colors... it goes down and becomes sound to us.... down farther, we perceive it as a heat... too low and we don't perceive it.

And the 'mass' (objects in our reality), their rate of vibration affects how we perceive them as well. A tree seems solid to us because it is vibrating at a speed that, compared to our body, feels near the same, we perceive both as solid. Things vibrating more slowly, we perceive as 'harder' than our body, comparatively. Things faster, seem more and more permeable, from water all the way up to a gas, and then beyond our conscious perception.

Technically, chemicals we release, like pheremones, are like little tiny, grouped units of vibrating energy. Everything is energy, at least so sez the physicists (not to mention quantum physicists). All the stuff vibrating close to our range, we perceive as reality. Stuff outside our physical perception, we think doesn't exist.

I won't go into the implication of that, but will get back to rocks, crystals and stones. ;-)

Since everything is energy, it's pretty much impossible to put something next to any life form that will NOT affect it. It's only possible to do it so that it's such a mild effect, we (and even the plant) are oblivious to it. Plants are affected by colors of light, by heat and cold, by sound -- as noted above, it's all energy, just at different rates.

Putting a rock (of any kind) in with a plant will matter at least fractionally, just like putting a marble or a gameboy or a stick of plastic etc. It's not just what something leeches (that is a 'major' energy transference, since actual mass is involved, and not just atoms, which it's said we trade with the things/people we're around constantly). Energy here being quite physical, not meta-physical. ;-)

Agriculture researchers discovered that red mulch (red within a certain range of frequency) would affect the yield of certain red fruiting plants, such as tomatoes and strawberries. It is thought that it's a matter of which frequencies are reflected when the sun shines on the plant. Still, if you'd told anybody 20 years ago that putting a red something under a tomato plant would inspire it to better yield, it would have been seen as really silly... but here we are.

Anyway. I don't know the effect of stones on plants. Some far better researched issues are still considered controversial. But given that all things in reality ARE constantly interacting with each other at the atomic level, I think everything in proximity has some effect, the only question is one of 'degree'.

And whether or not plants respond to our 'attention'--I suspect they are at least somewhat affected by it, but even if they aren't--most the point of having a plant is OUR enjoyment, right. So, if you like rocks and crystals, stick 'em in there. Why not?

PJ

PS the comment up there:
>plants found my collection of petrified wood... unsettling
That was truly hilarious. If I'd been drinking at the time, this laptop keyboard would be history!

The hydrangea in the photo is in bud; now blooming very pink.

After lots of googling, I found only one reference to crystals for plants, and that was that lepidolite was a stone known to be 'helpful for gardening and farming.' The only problem is that lepidolite has a Mohs softness of 2 1/2, which means that water will damage it. By the way, malachite is also low on the softness scale, and will be damaged by water. I guess you could wear a piece of jewelry made with lepidolite while gardening, but I wanted something to put in with my plants that would make them all specimens. :-)

Guess we are left with quartz crystals ... high on the Mohs scale of hardness, almost nothing will damage them. So if I add quartz crystals to my garden this year, and it does better than last year, is it because of the crystals, or because I have gone organic, or because I know a bit more about gardening than I did last year?? Heh.

But I also have seen some very interesting things when taking smaller sized boulders and creating a circle with them - THIS can affect the growth of plants around it and maybe even quite a ways away from it (like stonehenge type things) Again though I am talking about larger stones and a larger arrangement, not little stones. To go with little stones on top of the soil near the plant, if you wanted to have a good effect on the plants with them, you'd have to make sure they are great energy companions for and with the plant. I have yet to see any variety of plant that was good with the same type of stone. It'd be a very unique situation, something best looked at individually (through energy flow dynamics).....if you are not sure what that is about you could type in "subtle energy flow plants" in any search engine and probably come up with some basic information on it.

All stones on the desert surface preserve moisture in the soil beneath them, at least for a time. This is ancient knowledge: prehistoric Hohokam farmers of the Sonoran Desert used rocks as mulch around their agave plantings. In addition, translucent calcareous and siliceous minerals can transmit visible light, in some cases to depths approaching two inches, thus supporting photosynthesis below ground and under complete cover, much like a greenhouse. Measurements made by plant physiologist Frank Salisbury, of Utah State University, showed that about 1.5 percent of the sunlight striking the surface of a milky quartz stone penetrated a thickness of one inch; this means that as much energy reaches an algal colony beneath this stone on a sunny autumn day as is available to a potted plant in a typical, well-lighted office.

How fine and amazing this Earth!

We went there once for a lark, but it was so much trouble trying to chisel out these crystals that I decided just to take the big chunks of rock with the crystals in them and use them for landscaping. It's a pleasant effect when the sun shines. I can't say I've noticed much difference in plant growth, but it might help NY's economy if gardeners tried this.

On the metaphysical side, if one believes in the "sentience of vegetable matter", which Edgar Allan Poe postulated in the Fall of The House Of Usher, than maybe crystal therapy would be a good thing. I believe in plant sentience myself, that's why i think being a vegetarian is bogus, at least when you consume animals youu are eating the creatures that are murdering plants.