I know, the word "hydroponic" conjures up visions of long tanks, hoses pumps, and timers. Not this method. I stumbled on to the idea here and here so I have to give Ray Barkalow full credit, he has the © on the word Semi-Hydroponic©. I simply tried it and am reporting on my experiences here.
By nature I am compelled to modify established techniques and substitute available materials for proven materials. This is why the things you see here may differ from the tried and true methods described by Mr. Barkalow. I am not saying my modifications are better, just that they work.
Why do I use it? I am out of town for extended periods and needed a way for my roomates to keep my plants adequately watered. I am also one of the many people who compulsively attend to their plants, feeling subconsciously that my activity will cause activity (growth) in the plant, so I tend to water too often (incidentally, for the same reason I also have the urge to give the plants too much light too quickly). Semi-hydro prevents me from overwatering, and allows anyone else to easily care for my plants while I am away.
What is it? The basic idea is that you are providing the plant's roots with constant favorable conditions. This is imposible with the usual organic potting mixes (bark, sphagnum etc) because constant moisture promotes bacterial and fungal growth. These organisms break down and change the physical and chemical properties of the mix, creating unhealthy conditions for the roots. It is true that the roots of most orchids are designed to quickly absorb water, and then remain dry for extended periods of days or even months (see How an orchid grows and Orchids in the wild ). However, it is not true that an orchid's roots will die simply by remaining constantly wet . It is even possible to grow orchids in water.
For a discussion of this click here.
Semi-hydro is not so radical. Many people grow orchids using inert potting materials such as gravel, lava rock, perlite, charcoal, ground up tires etc. Semi-hydro growing is very similar except that the mix has a constant supply of water that is wicked to the roots by the potting medium. Build up of calcium and fertilizer salts is prevented by never allowing the pots to dry (so the salts can't precipitate) and by flushing the potting mix frequently.
But I need special pots, don't I? Not unless plastic is special! At its simplest you can sit a pot into a saucer of water. At its most complex you can buy multi-stage pots having a water level guage that are made for hydroponic growing. You can also use the inexpensive "self watering" pots available at places like Wall-Mart.
Seen here right to left:
5" round plastic pots sitting in saucers of water/fertilizer.
Modified 12 oz plastic cup (seen above).
Modified 32 oz deli salad containers.
What is my favorite pot? For ease of use and economics I mainly use 32 oz deli salad containers that I have modified by melting two or three holes through the side about 1.5 inches up from the bottom (see holes in the 12 oz cup at the top of the page). I use an inexpensive soldering iron to melt holes and slits in my plastic pots. For when the plants grow larger I will probably use something like modified 2.5 gallon buckets and rectangular plastic shoeboxes (depending on growth habit of the plant).
Why these pots? The basic design of the "three hole" pot is to allow one to fill up the pots and allow it to slowly drain at each watering, thus flushing and renewing the pot. This works fine outside or in a greenhouse, but would require hauling about a hundred plants to the sink each week in my apartment.
I water a little differently than most people who use semi-hydro (from what I understand). Instead of simply filling the pot with fertilizer water and letting it drain, I soak the whole pot in fertilizer solution for a couple of hours every few weeks. I do this to fully hydrate the potting mix and to get rid of any salt build up. The rest of the time I simply walk around the house every few days with a two gallon pump sprayer of water or fertilizer and spray the top of the pots to refill them. I use RO/distilled water so I don't know if my method would cause buildup problems using hard tap water.
By using the modified deli containers I can quickly nest them into unmodified containers to prevent the water from draining, fill them, have breakfast and then drain them (the drain water/fertilizer goes to the other houseplants). A sleeve of twenty five containers costs about $3.50. I now use the short 8 oz containers as coasters to catch any water that runs out the holes when I use the sprayer (the picture shows smaller lids from ice cream).
I often transfer small seedlings from 2" pots directly into the 32 oz containers. This is unless the mature size of the plant will be small and more appropriate for a 12 oz cup. Many of the problems associated with overpotting (excessive water retention and fast decay of potting mix) are not seen with semihydro growing.
I tend to buy small inexpensive plants from mail order companies in orders of around ten plants at a time to save money on shipping, so I really don't want to spend any more money on pots than I have to. It is much easier to find or make a few nice looking cache pots into which I can slip the deli containers when plants are in bloom than to keep all of the plants in nice pots. Lets face it, a nice looking pot is at least five to ten bucks.
Potting Mixes
The most important property of the media is that it wicks well, the second is that it does not float (if you are going to fill-flush the pots). Smooth surfaced, nonspherical, expanded clay pellets wick better than rough textured perfectly round pellets. Sponge rock (large perlite) used straight or mixed with charcoal is another popular mix, however perlite floats so a cap of gravel is used to hold it down and to slow evaporation (a cap of white aquarium gravel is shown below).
I have added charcoal to the clay pellets above because in organic mixes roots seem to bind to charcoal more so than to any other part of the mix (so I figure they like it). On the right is a mix of pumice, charcoal, and clay pellets with a base of clay pellets and a cap of white aquarium gravel. Pumice does not float and both absorbs and wicks water. I found it locally and used it as a substitute for perlite since I just don't like perlite (its a personal thing and has nothing to do with its properties --just like some people can't stand styrofoam or fingernails on a blackboard). Even though the pimice does not float when hydrated I have used the gravel cap here to slow evaporation and provide reflected light to the plant. This increases the efficiency of my orchidaria lights, but I will probably discontinue the practice. I did it on a whim to see what would happen. It tends to get in the way slightly, but it looks good. I use the clay pellet base to provide larger airspaces in the lower region of the pot. It is probably unnecessary.
The half inch clay pellets used alone work fine for both very thick rooted and very thin rooted plants. The pumice mix works well for those same plants. I have not seen any consistent differences in growth to prompt me to choose one vs another for a particular type of plant.
Fertilizer I use Jerry's Grow as recommended for normal usage. To provide calcium, I use water with gypsum (calcium sulfate) dissolved in it about once a month at 1 tbsp/gallon. If the mood strikes me I may use epsom salts (at 1-2 tbsp/gallon) a couple of times a year to supplement magnesium. It is probably not needed since Jerry's Grow contains a balanced supply of magnesium, but it can't hurt either. I can't comment on the use of normal crystalized fertilizers, but would suspect that your usual "weakly weekly" fertilizer in tap water would work fine.
What orchids can you grow using this method? I'm not sure what the range is as far as temperamental or specialized plants may be. Here is what I am growing. Grow List.
