Questions about fertilizing Phalaenopsis

[Ray]

Also, please consider the fact that putting a "drainage" layer of pot shards or styrofoam peanuts in the bottom of the pot actually makes the potting medium hold more water.

Water is retained in the medium by absorption and by surface tension holding it between the particles. Absorption is determined by the materials used. How well surface tension holds water in the medium is determined by two factors: the size of the spaces (smaller = more is held), and gravity.

If the top-to-bottom "column height" is relatively large, the weight of the interstitial water above will overcome the surface tension and the medium will drain. If that column is reduced in height, there is less mass to overcome the surface tension, so it won't drain as well.

You can prove this for yourself in the kitchen: submerge and saturate a sponge. Lift it out of the water in a horizontal orientation (parallel to the water surface), until it has stopped dripping. Now rotate it so the longest dimension is vertical - more water will drain.

[bil]

Originally Posted by Subrosa

Good system, just one observation. If you think out and properly size the smaller pot (or whatever you use as a pedestal) you don't need to worry about removing excess water. Measure twice, manually drain never!

Well, tbh, that's only a problem if you overwater. Normally I stop fast enough so that by the next time I water, the 'catch' saucer has dried out.

On the Cymbs, which are in quite big pots, it takes so long for the water to run thru, that when it does there is too much to dry, so then I suck out the surplus.

[Orchid Whisperer]

Originally Posted by Ray

Also, please consider the fact that putting a "drainage" layer of pot shards or styrofoam peanuts in the bottom of the pot actually makes the potting medium hold more water.

Incorrect.

Originally Posted by Ray

Water is retained in the medium by absorption and by surface tension holding it between the particles. Absorption is determined by the materials used. How well surface tension holds water in the medium is determined by two factors: the size of the spaces (smaller = more is held), and gravity.

Correct.

Ray, the size of the spaces between particles is also related to sorting (the degree to which the particles are the same size - particles that are all roughly the same size are well sorted (more open spaces), a material composed of many sizes will be poorly sorted). If you have large particles that are all roughly the same size (styrofoam peanuts) the spaces between them will be large and will drain well. Try filling a clay plant pot with styrofoam peanuts, then stick it under a running faucet; you will have a very tough time trying to fill that pot with water! To make it more like a potted orchid, fill only the bottom 1/3 with styrofoam peanuts, the rest of the pot with a typical orchid mix & repeat the experiment. It will still drain rapidly. I have potted using a drainage layer & even after 3 years, even if the orchid medium has degraded, there are still many large pores in the styrofoam peanut layer.

[Ray]

Have you tried the sponge thing?

Last time I checked, styro peanuts are really not a practical medium, and that is not what I was referring to.

Pick a 6" tall plastic tube. Fill it 100% with a standard medium, and weigh it. Then saturate it, let it drain, and weigh it again. Fill the bottom half with your open peanuts and the top half with that same medium, and weight that. Repeat the process as before - saturate it, let it drain, and weigh again. The mass of the water will be greater than 50% of the first reading.

With a shorter column of medium, the mass of moisture-per-volume increases. The total mass likely will decrease.

A law of nature (physics), not an opinion of Ray.

[Orchid Whisperer]

Styrofoam peanuts (SP) work very well as an inert material in the bottom of pots, facilitating drainage. Growers have been using them for many years.

Ray, the experiment you just proposed in your last post has nothing to do with your original statement! If you take a moderately sorted material with a range of particle sizes (such as orchid mix; OM) it will have less effective porosity than a well sorted material of equal size particles (SP). Let's say the OM has 20% porosity, the SP 30%. Fill the pores in the OM with water (let's ignore for the moment that both materials will float out when the containers are filled with water), then the pores in the SP then OF COURSE there will be more water in the SP!!

But we don't grow orchids SATURATED. They are grown with the materials drained. Your experiment just confirms that the pore space maintained in the drained SP is greater.

Work through the physics of that, or maybe I should say Hydrology 101.

[Ray]

Boy! You really know how to overlook the "forest" for the sake of individual "trees", don't you?

If you're not watering your orchid media to saturation - which then drains - then you're not doing a very good jobs of flushing, so that creates other problems.

With the exception of media in which the void space is so large that there is only a minuscule amount of surface tension-held water (hence non-communicating) A tall column of medium will hold less free water-per-volume than will a short column of the same medium.

That applies to soils, sphagnum, bark, etc., all which act, to some degree, like a sponge. (I'll bet you haven't tried that experiment yet.) That's basic hydrology, too.

[Orchid Whisperer]

Ray - I stand by my original statement - your original claim regarding drainage materials is flat-out wrong.

I'll not continue arguing this off-topic point and further highjack this thread. Perhaps you can post about the hydrology of kitchen sponges on you own thread.

- Using science and logic to point out baloney when I see it.

[Ray]

Just take a look at THIS, a University of Wisconsin dissertation from 1926 - pretty basic, and experimentally proven hydrology.

Sure, it covers soils, but the science is solid and broadly applicable, especially to orchid media that are fine and have small spaces (sphagnum comes to mind).

( I try my best to work with scientific facts, and also to not be petty or insulting.)

[ccrow]

I like to water mine in the sink(lots of toting back & forth; that's why they mostly live in/near the kitchen). So I use the sprayer to rinse them down but have the drain closed and let them soak for 5-10 min. Then I take them out to drain, and get water out of the growing points, before I put them back. For fertilizing, I do the same thing except I mix the fertilizer in my watering can and water them with that instead of the sprayer- letting them soak as above. I also do not fertilize every time, so salts won't build up.

[bil]

Originally Posted by ccrow

I like to water mine in the sink(lots of toting back & forth; that's why they mostly live in/near the kitchen). So I use the sprayer to rinse them down but have the drain closed and let them soak for 5-10 min. Then I take them out to drain, and get water out of the growing points, before I put them back. For fertilizing, I do the same thing except I mix the fertilizer in my watering can and water them with that instead of the sprayer- letting them soak as above. I also do not fertilize every time, so salts won't build up.

If you use the minimum dose on each and every watering, and let a bit of the solution run thru, then salt buildup won't happen. Plus it's more natural.