Phragmipedium fertilizer build up -> rinse?

[tropterrarium]

I just have one Phrag. pearcei. Phrags like to sit in water, so I put it in a deep tray, and water with RO & fertilizer (around 300 TDS). Once it dries up in tray (sphagnum still wet), I water again with fertilizer, … Water evaporates, but excess fertilizer does not wash away like in most other pots, because the pot sits in a deep dish.

So I did an experiment, and rinsed the pot with pure RO and stuck a TDS meter in the run-off: 1900. Yep, one thousand nine hundred. Seems a bit much.

First, is this a problem, or do I invent problems?
If that TDS count is too high, how do you keep it in check?
I rinsed my pot several times with pure RO, but given the thick sphagnum, a lot of nutrients are absorbed by it. Took about 5 washes to get it below 800.

Any old Phrag. hands having any insights?

[quiltergal]

Phrags are not heavy feeders. You can probably fertilize once a month and be just fine. I would also dilute the fertilizer more than you would for your other orchids. Are you using a clay or plastic pot & saucer. I would recommend using plastic as it does not collect TDS like clay does.

[jeremyinsf]

Originally Posted by tropterrarium

First, is this a problem, or do I invent problems?
If that TDS count is too high, how do you keep it in check?
I rinsed my pot several times with pure RO, but given the thick sphagnum, a lot of nutrients are absorbed by it. Took about 5 washes to get it below 800.

Any old Phrag. hands having any insights?

You are inventing a problem! The run-off means lots of other stuff from the media is... running off... into the water as it drains. So, that means you are not going to get 'pure' water out of it. You don't have a problem here. It only went lower because you kept flushing it many many times, and in doing so, less other stuff was running into the runoff.

Focus on what you are putting into it, as that is what counts. What's your base TDS, before you mix in your fertilizer?

I fertilize at about 50ppm about every 10 days or so.

[tropterrarium]

Thanks for your replies. Re pot and saucer, it is a plastic mesh basket in a 1.5" tall glass pan. So no issues with introducing much into the water.

Re RO start TDS, its about 25.
Thanks for the pointer re rather low feeding requirements. Will lower to once or twice a month, rest just pure RO.

Good point re stuff coming out of the medium. Will have to see what virgin sphagnum gives off, could be illuminating.

[naoki]

Checking TDS (or EC) and pH is a good way to check the environment around the roots (for any orchids). And your measurement indicates that your method is causing some salt accumulation. There appear to be several methods how researchers measure "run-off". One method is that you do normal watering (or fertilizing). Then wait 1 hour or so, and pour a small amount of water for the measurement.

I've been growing only 6-7 phrags, but I wouldn't bottom water with fertilizer. As it starts to evaporate, the concentration increases. So when I fertilize, I let the water drain (and not catch in the saucer). Then I put pure water in the saucer. I also don't let the water in the saucer evaporate too much. So between the fertilizer (very weak as Jeremy and Terri mentioned), I keep top watering every or every couple days with pure water. Not just topping off, but replacing the significant amount of water in the saucer (to avoid the problem you experienced).

[jeremyinsf]

Originally Posted by naoki

As it starts to evaporate, the concentration increases. So when I fertilize, I let the water with drain (and not catch in the saucer). Then I put pure water in the saucer.

Totally agree with this and would also add that it's especially important if you are using seaweed to NOT just let that treatment sit in the saucer - you don't want it to drink that stuff for several days or whatnot.

[hagfish]

Mine is a hybrid named "uranus". I have found it tolerates ordinary tap water as long as I let the water run out the bottom of the pot. My water is extremely hard, but the plant still grows, even with the chloramines in the water. My understanding is that species tend to be more delicate than hybrids, so perhaps they are not quite as lime tolerant. Maybe a chelating agent may speed up the elimination of fertilizer salts. EDTA (EthylamineDiamineTetraAcetate) is an organic compound which binds to metal salts and makes them soluble. Miracle Grow fertilizer uses it to enhance the uptake of nutrients in hard water. The best thing to do is perhaps stop fertilizing completely and allow the plant to sit in distilled or RO water. Change the water and measure the dissolved salts. My phrag grows like a weed and I seldom fertilize it. Yours can probably survive quite well without any fertilizer for several months.

[Ray]

Let's look at the physics of what's going on:

nutrient solution absorbed and wicked in the medium has a great deal more surface area than does that tray, so essentially all of the evaporation is occurring at the top surface of the medium, working its way down into the pot as the upper part dry.

As the water evaporates the dissolved minerals and plant wastes will precipitate, and build up on the particles.

Personally, I'd add fairly frequent plain-water flushes to your regimen.