Thanks for the informative post, Bob!
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This is a discussion on BiminiBob's Semi-Hydroponic orchid Tips within the Semi Hydro / Lights / Greenhouses / Accessories forums, part of the Orchid Culture category; ...
In the November 2006 issue of Orchids magazine pages 840-843, I was fortunate enough to read the article by Charles Rhodes entitled “No Longer A Killer.” This launched the beginning of a very pleasurable hobby. Prior to this growing strategy I was a bona fide KILLER. Sometimes they lasted a while but generally not for long and I was very discouraged. Below I would like to outline some of what I have learned from this magazine article, and from other on-line references. From that base and my own experimentation and observation I have evolved a system that is satisfying and low maintenance. These techniques (very painfully learned) have brought me to a point of near 100% confidence that I can purchase a new and lovely “treasure” and have it not only survive but thrive! Even those with poor roots usually do well. Every commercial grower and successful hobbyist has worked out their own system but the variables of one’s own schedule for work, travel, etc. plus your growing space and location result in variations in sunlight, watering, fertilizing, etc. The commercial growers regulate this very closely but some times we can not. So let’s make it simple:
1) NON ORGANIC MEDIA: All types of bark, sphagnum, etc. eventually decompose and rot, thus here cometh the root eating bacteria. Orchids need a substrate for moisture and air and someplace to cling to. Various types or rock and manufactured media are available and each has its own attributes. Here are my favorites:
A) Light Weight Expanded Aggregates (LECA) – a light weight expanded silica-clay pellet that not only retains moisture but has the capacity for capillarity or “wicking”, i.e. the ability to draw moisture up and through-out the media. The round nature of these pellets provides good air flow within the media. Two popular brandsof this type of material are Hydroton and Primagra. Other types and brands of “rock” are also used but an important characterist needs to be that of capillarity. Most of my experience is with the hydroton because it is locally available.
B) Diatomaceous Rock: There are several brands of this type of natural rock that is modified by heat and other techniques and contains a high amount of silica. From what I have observed it holds moisture very well, has reasonably good interspace for aeration but does not have the ability for wicking/moisture transfer up into the media found in the LECA material. All of these medias should be rinsed and soaked in water overnight and kept soaked until placed into the container.
Using these types of media, the size of the pots is less critical. Common “wisdom” claims that the roots grow best out near the sides of the pot to reach better oxygenation—with the rock or pebbles the entire pot is well aerated.
2) CONTAINERS: Various websites market a variety of plastic pots that are durable and have a manufactured set of two small holes up on the SIDE of the pot (with no holes in the bottom). Any non-vented plastic pot can be modified by burning holes ( approx. 1 1/8” up from bottom) with a soldering iron. This is the essence of the semi-hydroponic technique. The media at the bottom of the pot is fluid saturated and that above
receives moisture by the capillary action described above, wetter at the bottom to drier above. Now we have rather constant moisture and air through-out the pot. VIP! The media needs to be stacked about ¾ inch above the level of the holes(and fluid) prior to adding the plant so the roots never sit in the water! This technique works great for almost any orchid I have dealt with so far. A special point should also be made that when watering/fertilizing, do so from the side of the pot so that the main root base of plant does not become too wet. Also, as commonly known, keep the crowns of the phals and phrags absolutely dry! And very importantly, occasionally “flush” the pots thoroughly with the water hose ( I do this every 2 weeks) to remove retained salts, etc.
3) FERTILIZER: The two I have used are DynaGrow’s “liquid grow” 7-9-5 and MSU (Michigan State) liquid but various others are available. There are some differences but both seem to work well. Add 5 ml ( 1 teaspoon) per gallon to the watering solution and keep the reservoir in the pots wetand do not let them dry out. Other additives such as pH modifiers and cell stabilizers may be used as well. In the open bottom/saucer technique described below, I use conventional fertilizing, e.g. nutricote (dynamite) 180 day into the pots plus weekly spraying of dilute general purpose fertililizer. With the initial re-potting I soak the rock media in the liquid fertilizer plus add a root stimulator. Do not use this high concentration solution thereafter as it will damage the roots! For those plants that start out with poor roots a very dilute solution of the stimulator may be added until the roots flourish.
Now we have what I would like to call the “MIGHTY TRIAD” of constant moisture, constant air and constant nutrition. This eliminates the most troublesome variables!
SUNLIGHT: You know what to do here.
AIR FLOW: Always a good thing.
CONTAINER VARIATIONS: This gets creative. When I started growing outside of my screened porch, a problem was encountered. Detritus from leaves, pollen, etc. would fall into the pots collecting in the bottom reservoir and create rot. This mandates more frequent flushing and “tipping” of the pots to drain all of the water out of the bottom. Coconut fiber can be placed in the top of the pots to act as a filter to prevent the leaves from falling down into the media; this is effective but labor intensive. These classic semi-hydro pots are in fact a semi-closed system with poor drainage and this is a weak link for outdoor growing. The plants, however thrive outdoors. Now for the variations. We all know that different species have varying water needs. The various LECA and rock media retain and wick water differently and some fine tuning for your type of orchid is needed. Thus if we place a standard orchid pot with holes in the bottom onto a saucer, this creates a reservoir of water, i.e. Semi-Hydoponic. The type of pot can vary as classically known: slits up the side and/or clay allow more air and dry out easier ( for cattleyas and other “dry side” orchids). Plants requiring intermediate “wetness (dendrobiums, oncidiums) would probably go into a clay pot with no side vents plus the saucer and those requiring high moisture (phaleonopsis, prhragmipediums, etc.) would go into a plastic pot plus the saucer. The relatively cheap plastic pot/saucer combos from the home supply stores may also be used for any and all by simply adding some side holes into the pots with a small soldering iron, more holes—more air. These pots are easy to hang using vanda wire hangers and small holes in the rim of pot. With a little ingenuity the saucer may also be attached to the hanging pot thus yielding considerable flexibility as to where your orchid is placed. The saucer technique may be tuned a bit for the outside plants—if there is rain several days in a row, simply remove the saucer temporarily and the rain will not overwhelm the potting media. Remember that all of this rock-type media will dry out much faster than bark and watering habits need to be adjusted accordingly. I also pot many of my cattleyas in tight meshed baskets with the pebbles only but are watered daily—this works great.
For all new plants that I purchase with marginal root structure, these are placed first into the true Semi-Hydro pot, this would include keikis and rootings. After the roots become large and healthy, I transfer them to one of the above open saucer or open air techniques for simplicity and low maintenance. One “heretical” thing I have done routinely for several years, and have yet to regret, is to repot any new orchid, even if fully blooming!! I have not lost any blooms and believe this is a better long term strategy to protect and nurture the plant. If the plant is already potted in a rock media, I might leave this alone until repotting would normally be required. An observation about repotting after transitioning from the semi-hydro pots is the amazing root structure present with rarely any root rot at all! Obviously this makes any re-pot a much simpler task—simply pull the plant out and place it into a larger pot and add more media!
That’s it for now but the above is still a work in progress. However, these techniques noted above have made my orchid “addiction” much less painful!
Thanks for the informative post, Bob!
Bob, Thank you for this article. It expounds on some of the things I have noticed. I suggest that anyone planting oncidiums in LECA (particularly if using the smaller LECA) place the base of the plant just above the stones, so ONLY the roots are covered. The oncidiums I have seem to draw moisture up into the formerly dry sheaths around the pbulbs if the base of them is touching with the leca. Thsi will lead to rot.
thanks, this explains why some of my the orchids i bought are potted using some forms of
gravel, instead of coco husks.
I use orchid diatomite rock and I have very good results with them. No need to worry about overwatering as diatomaceous rock dry out quickly but retains good moisture.
yes i remembered you mentioned that during our brief meeting. you gave a good pitch
for it thats why i bought a bag of it from SM, and so far so good, im happy with it, the
chids are happy with it. the only thing is that those sold in SM are quite a big lump of
rock that you have to smash it with a hammer to get some manageable size. Other
than that I'm so happy with it. I even saw one that is a powdered version of it.
thanks for sharing with me that info.
The powdered version of diatomite rock that is being sold in SM I think is being sold as an odorizer for garbage cans.
I just use my hands to break the large pieces into smaller ones. The smaller bits and pieces I can even mix with my regular organic potting material for my soil-based plants so that the potting mixture becomes more porous and open and gives better drainage.
I do not use 100% diatomous rock for the orchid mix. I normally would use the rock as the base material instead of charcoal - that way the excess water that collects inside the pots is absorbed by the rock so there are no "pools" of stagnant water inside the pot and keeps the media from getting overly wet. I would use basic potting material like organic bark, osmunda, tree fern bark, sphagnmum moss or whatever as a top material. I do this since diatomaceous rock does not have any nutrients by itself. At least the top layer of organic material I place will provide this (aside from the fertilizing I do). Just be aware that you should flush the pot thoroughly with water at least once a month) to wash out any accumulated salts over time to keep them from damaging roots of orchids.
thanks for the pointers, i appreciate that. what i did what that i hammered it to smaller
pieces then applied my mix of cocopeat/perlite/charcoal, but i only do this for my paphs.
for the oncidium, maxilliara, phal i've placed them in straight diatomite. So you think i
should put some of those mix there.
For the phals you need to increase the humidity a bit. Most phals I see sold in the nurseries come from taiwan and I notice they use sphagnum. The only problem is that sphagnum retains too much water and can get soggy wet so what I did was to replace the moss with smaller pieces of rock as the base plantuing material and then added some organic material like the wood chips to give some organic nourishment. I used to place some of the original moss but where I grow my plants it gets pretty wet so I took out the moss altogether.
Refer to my previous comments about semi-hydroponic culture; I would offer some "upgrades" to those techniques. The weak links noted over time are: 1) with the classic SH pot there persists a residual of water & salts in the bottom, freq. tipping of the pot helps but is labor intensive. 2)With even mod. sunlight green algae forms on the media, also a problem 3)Outsoors, the leaves, etc. contaminate the media--another pain. SOLUTION: From a box store I procure opaque, plastic pots with a mated botton saucer. This saucer now forms the SH reservoir and easily flushes out with watering. Use a soldering iron (or drill) to create several side holes on the pot just above the level of fluid to allow some air to flow and better aerate the media. These pots can be hung with vanda wire or put on stands, benches, etc. Each pot may be customized with more or less holes or without a saucer for the type of orchid and desired aeration. This system may be used with clay pots +/- saucers for similar control of moisture and aeration--it works great, especially for growing outdoors where conditions vary greatly.