Growing Orchids in Rock

[Lars Kurth]

I have received a few plants from SBOE this year (Schomburgkia's & Oncidium) and they were grown in rock, even plants in hanging baskets. I was intrigued as the plants had an exceptional root system with roots that were also very "frothy" (the root system had a large amount of feeder roots - aka roots with fine hair on them).

I was wondering what the in and outs of rock culture for orchids are and whether anybody has any experience. There do not seem to be an awful lot of articles about rock culture on the web.

[tucker85]

Here in South Florida people grow orchids in several different kinds of rock. Hydroton (LECA) is a man made clay rock and is the most common. I grow all my cattleyas in it. Other popular rock mediums are Dyna Rok II (light colored stone) and Stalite (dark gray stone). I know two commercial growers who use Stalite exclusively with excellent results. The advantage is that rock medium doesn't break down over time like fir bark. Also it's very difficult to overwater plants grown in rock. In Florida, bark decomposes very quickly. I don't grow Schomburgkia. Oncidium have fine roots and my experience has been that they grow better in coconut husk chips although they will grow in rock medium. In South Florida's hot humid weather I find that rock mediums are excellent for cattleya and laelia.

[Lars Kurth]

I think it is Stalite: the substrate looks a little like granite but is much lighter.

[keithrs]

SBOE grows in granite almost exclusively. Like tucker said, those are the many advantages to rock. The main disadvantage is that it is heavy. I grow in LECA and Higromite mix because it's pretty cheap to buy and it retains water better than rock, and it alot lighter. Like tucker, I like coco for my fine root plants other than Tolumnia which I grow in higromite in 2" baskets and let it go wild.

Another thing is that you can double pot.

[peeweelovesbooks]

Yeah, SBOE grows in rock. I grow in LECA, even my schomburgkias.

For top heavy plants, I mix LECA and river rock to make sure the plant is properly weighed down.

I do not double pot, nor am I a proponent of it. I think it looks sloppy and messy. IMHO. I repot everything when I get it--even if it's from SBOE.

[King_of_orchid_growing:)]

Products such as DynaRok or Aussie Gold are rock based potting media. The rocks they use is called diatomite.

Diatomite is a silica based mud rock formed from the silicon structures of fossilized diatoms. It is highly porous and can retain a lot of water. Water is not held at the surface of the rocks, but rather it is mostly held within the pores of the rocks. Because the water is not held at the rock's surface, the rocks release the water slowly and doesn't drown the roots (water on the surfaces of rocks tend to have the same effect as standing bodies of water). The pores on/in these rocks are more or less a bit uniform in size from one another.

Semi-hydroponic materials such as LECA, PrimeAgra, and Hydroton work on the same principal. They are porous, inert materials and the water is held mostly within the pores, with a small percentage of water being held on the surface, and are slowly released to the plants. The pores on/in these semi-hydroponic materials are more or less somewhat uniform in size from one another.

Other porous rocks that are commonly used in horticulture are perlite, pumice, and volcanic rocks (red or black). Of these rocks, volcanic rocks not only store water in the irregularly sized pores, but they also tend to retain water on the surfaces of the rocks more so than either pumice or perlite (I'm not sure why, but I suspect it may have something to do with the presence of volcanic glass in its composition).

Granite is not so widely used as a horticultural material, although there are some people who do use it. I guess depending on the granite, it has low porosity. It is still usable as a potting material because it can still retain some water.

Stalite is a material I'm not too familiar with, but it can definitely be used as a potting material as well.


Btw, not all orchids are exclusively epiphytes. Some do grow as lithophytes and epiphytes. There are others that grow as epiphytes, lithophytes, and terrestrials!

As a side note, while it hasn't been verified, I assume that the ability for epiphytes to also be grown as lithophytes is showing the evolutionary transition that orchids made from being solely terrestrial plants, to lithophytes, to epiphytes.

[stefpix]

I bought Floor-Dry from Napa auto (part # XXX-8822).
It is diatomite fine gravel that can be used for horticulture. Similar sized to common fine perlite. I want to try to grow houseplants in it. Maybe mixed with little soil / or gravel. I have been reading that a lot of potted plants fo better in a gritty mix than in peat based commonly available soils.


With rocks in general you may have to provide more fertilizer as it is an inorganic medium so there is not natural fertilization from the break down of bark. I always mix anyway some LECA in the medium.
I think with rocks you may need higher humidity.

[orchids3]

My cymbidiums are all in Stalite gravel. It does well for me in NE Florida. Have tried 100% stalite and the plants do OK but think mixing a little organic material in the top layers helps the plants grow. Have used CHC as the organic material and here lately am trying a little crushed Tree Fern. Have not used the Tree fern long enough to be sure that is a good ideal but it is working so far. I also incorporate a sprinkling of diatomite (Floor dry)
I use the stalite with all my plants - Paphs and Phrags seem to be doing OK but did use quite a lot of CHC (About 1:1 with some diatomite seems to be doing the best) Dendrobiums seem to like 100% stalite - etc etc.
I really like the stuff. It does take some adjustment of the diatomite, Organic matetial to stalite ratio to get good results with differant plants and watering habits. Do not have it perfected by any stretch. If you use floor dry make sure it is 100% diatomite not something else. Agree with NAPA as a source.

[WhiteRabbit]

I have a few Catt alliance plants potted in straight pumice - they seem to love it! Can be quite dry here in summer, so during that period, I leave them in a saucer with a bit of water - they aren't constantly sitting in water tho - water is gone after a day or two (depending on the temp and humidity) - I give them more water a day or two after that (as Tucker said, it's hard to over-water in this media, tho possible in cool, damp weather) In cool, damp weather, I just water anywhere from twice a week, a week, or even a bit longer, depending on the temp, humidity, if plant is indoors or outdoors, but don't leave them sitting in water at all.

I have a few Dens in pumice/perlite combo that are doing well too - these are plants that don't want to dry out, and perlite retains moisture very well.

Because of the porosity of pumice and perlite, I give the media an extra good flushing at least once a month.

I haven't tried any Oncidium alliance in this type of media.

[harleymc]

I've used sandstone chips for smaller Dendrobium speciosum (local rock for a local orchid) and have used a bubbly / porous basalt for sarcochilus. Both were great but the pots were very heavy, so i'm back to a bark/coir/perlite mix (my back thanks me).
Crushed terracotta brick is also interesting as a medium but soak it for a few days/ water changes first to remove excess salts.