Questions about using lava rock - Orchid Board

Orchid Whisperer · #1 05-09-2014, 09:14 AM

I have a Dendrobium spectabile, an Encyclia cordigera, and an Epc. Charlie Brown that I want to re-pot into lava rock this summer. I would like a bit of feedback from users experienced with using lava rock as a medium.

It seems like red lava rock is the most commonly used type. However, the only kind that I was able to get locally is the black variety. The only difference between the red & black that I have read is that the black tends to get hotter in the sun; I think I can take care of this problem by using a layer of white quartz pebbles on the top of the medium (white reflecting light, etc.). Are there any other differences between the red & black that I should be aware of?

Preparation of the lava rock. My understanding is that the lava rock in the bag is unsorted & will need to sorted into very coarse, coarse, medium and fine grades. Also, it should be washed and rinsed to remove fine materials. Anything else? I was thinking that mixing styrofoam packing peanuts in with the lava rock in the bottom of the pot might be beneficial from a weight standpoint.

I have read that long-term care will need to include a monthly clean-water soak and rinse to remove salt build up.

Are there genera that do really well (or really poorly) in lava rock?

Any and all suggestions or advice would be appreciated!

ALToronto · #2 05-09-2014, 09:32 AM

I've put a lot of my plants into lava rock, and they're all doing well. I use both red and black. The difference is the temperature that the lava reached - red was formed at a hotter temp. I haven't seen a difference in performance.

Rule #1: YOU MUST WATER EVERY DAY. If you cannot, don't do it. On some of my plants, i have a layer of sphagnum on top, and I can skip a day. But plain lava rock will dry out in a few hours.

Because I water every day, I don't get a salt buildup. I also use RO water and fertilize sparingly - 10-20 ppm N at every watering, using a fert made for RO water (Dyna-Gro Grow and K-lite).

There are no other rules to lava rock. Plants that like being mounted do very well in it. Don't put slippers in it, though.

Size doesn't matter much. I tend to put bigger pieces at the bottom.

Leafmite · #3 05-09-2014, 10:04 AM

Always rinse the rock in a bowl or outside. The dust can clog drains. I put the big pieces in the bottom, too, and sometimes in the middle. I use net pots so I can enjoy seeing the roots and to promote the most even drying. I also found the clay pots just too heavy for my shelves.
I find my zygos and Burr. Nelly Isler need a layer of sphagnum moss to do well for me in the red lava rock. I don't grow slipper orchids now but I did successfully grow three paphs for quite a while in red lava rock (watering twice a day) until I came to the realization that I am just not fond of slipper orchids.

Cym Ladye · #4 05-09-2014, 11:13 AM

Be careful which red lava rock you use, as some will attract calcium and other minerals if you do not have water very low in salts. Within a year the rock will become so toxic to the roots of an orchid that they will die when they come in contact them.

ALToronto · #5 05-09-2014, 12:09 PM

Quote:

Originally Posted by Cym Ladye

Be careful which red lava rock you use, as some will attract calcium and other minerals if you do not have water very low in salts. Within a year the rock will become so toxic to the roots of an orchid that they will die when they come in contact them.

Calcium is not toxic to orchids - many do well in dolomite, which is mostly Calcium Carbonate. However, people who follow the labels on fertiliser containers and think that "1/4 strength" is low dosage will soon poison any medium with excessive fertiliser salts. Do the math to determine the dosage you need to get no more than 20 ppm N (ppm = milligrams / litre). As a rough guide, if you detect a trace of colour in your water from the fertiliser, you're using too much.

My Green Pets · #6 05-09-2014, 12:44 PM

Quote:

Originally Posted by Leafmite

...until I came to the realization that I am just not fond of slipper orchids.

Heresy!!!

I have my catts and oncidiums in red lava rock. Our tap water is pretty low in salts but reading this thread, I see that I need to be very careful to flush them regularly. Lots of good tips above.

Leafmite · #7 05-09-2014, 01:23 PM

Cym Ladye has a good point. I put my orchids outside and we tend to have heavy rains in the summer with the big thunderstorms and that helps to flush the lava rock.
We live where the water requires a water softener so I cannot use this water. I use distilled/rain water and with the red lava rock, I had to experiment to get the fertilizer balanced. I usually put some Ironite in the bottom of my selected watering can and then add a bit of Epsom salts and powdered milk along with the fertilizer for each watering. Egg shells are put among the rock (it doesn't provide calcium immediately but after it begins to decompose, it provides a steady source). I use an MSU fertilizer and alternate with Bettergro. I have been doing this for a couple of years, ever since I had problems with the calcium deficiency disaster when I stopped using goldfish pond water (that was the only fertilizer I used previously...with the pond tablets for the lilies and lotus and fish waste, the plants really thrived).
Over all, I really love using red lava rock as I don't like re-potting or worrying about my roots when we have a week or so of rain.
Good luck!

---------- Post added at 01:23 PM ---------- Previous post was at 01:19 PM ----------

Yeah, I know. My orchid society is very into paphs so I did buy the three and tried to convince myself that I loved them. I do love their fuzzy roots, though, I admit, and the dark ones look very cool when in bud. I'm just not fond of the blooms. I do go through phases, though, and it is always possible I will, at some point, want a few again. :0

khill · #8 05-09-2014, 03:59 PM

I love Lava Rock! I use the black and have great results with Cattleyas, Epicats, Encylias, Dendrobiums and the like. It never breaks down and I don't have to worry about too much water in the summer, as I grow outside in SW Florida. I currently have a Epc. Charlie Brown in bloom with a new shoot growing in lava rock.

The summer rains flush the pots. I fertilize about every 2-3 weeks and have no problems. I don't fertilize as much in the winter months. My Phals I do mix in some moss with the rock for added moisture retention but overall love the medium. A local orchid nursery recommended to me this method when I began growing and it has worked well in my conditions.

I have a Bc. Makai that I have never repotted in 7 years in lava rock. I can't find the rock anymore as it has grown all around it. It is a monster but gorgeous when it blooms and no worries about medium breakdown.

Hope this is helpful.

hanzy08 · #9 05-09-2014, 08:27 PM

I bought a miltoniopsis planted in lava rock and I had to water the thing everyday. I missed watering for 3 days cause I was away and the plant shriveled really bad. I also have a dendrobium planted on this medium and water everyday. I don't hate it but sometimes I just don't have the time to water daily or twice a day for water hog plants.

Optimist · #10 05-09-2014, 08:55 PM

I love lava rocks mostly with any kind of Cattleya, like Blc or Lc. As to whether red or black, I cannot say. By the laws of physics, black attracts more heat, but red is not so far behind it in the color spectrum. I use red because it is local and available here in this part of the country where I live. I certainly would buy locally, since in my mind there is not much of a difference.