Leaf edges turning yellow in hydroponics

[Ray]

Originally Posted by miss.jakyak

I have it on a schedule of 5 days in water (the 3 big roots pointing downwards), 2 hours in fertiliser (concentration: 1 teaspoon per 500mL water), 2 days of drying out. All the small roots pointing up are new!

Do you think it's time to repot it though? Maybe the hydroponics have done what they need to do?

That strikes me as a very odd schedule. Consider that an active ebb-and-flow hydroponic setup will expose the roots for a matter of minutes, then drain, exposing the roots to air, with that cycle repeated several times a day. It doesn’t take the velamen on a root but a matter of seconds to become saturated, and the absorption process after that is much slower. I would think that a daily hour soak would be more appropriate, but that plant seems OK from a hydration standpoint.

Now, as to nutrition. After 5 days in water, the roots are SO saturated that they are probably unable to take up but a tiny fraction of the fertilizer. You’d be far better off adding fertilizer to the water before you start the soak phase. The velamen layer is like a sponge, able to absorb a lot more when dry than when saturated.

“1 teaspoon in 500 ml” tells us very little to help you address the issue. What is the fertilizer formula? 1 teaspoon of Dyna-Gro 7-9-6 is a lot different than a teaspoon of Miracle Grow 30-10-10. Under your current 5 days wet/2 days dry schedule, I’d recommend 25 ppm N. If you divide 2.3 by the %N in your formula, the result is ml/L to mix with the water. Using my two examples, that would be 2.3/7= about 1/3 ml/L for the Dyna-Gro and 2.3/30=0.08ml/L for the Miracle Grow.

As to potting it up, be aware that changing to a standard medium after having been grown in water is likely to result in some root loss, but as expensive as that root system is, it’ll probably bounce back fine.

[miss.jakyak]

Originally Posted by Ray

That strikes me as a very odd schedule. Consider that an active ebb-and-flow hydroponic setup will expose the roots for a matter of minutes, then drain, exposing the roots to air, with that cycle repeated several times a day. It doesn’t take the velamen on a root but a matter of seconds to become saturated, and the absorption process after that is much slower. I would think that a daily hour soak would be more appropriate, but that plant seems OK from a hydration standpoint.

Now, as to nutrition. After 5 days in water, the roots are SO saturated that they are probably unable to take up but a tiny fraction of the fertilizer. You’d be far better off adding fertilizer to the water before you start the soak phase. The velamen layer is like a sponge, able to absorb a lot more when dry than when saturated.

“1 teaspoon in 500 ml” tells us very little to help you address the issue. What is the fertilizer formula? 1 teaspoon of Dyna-Gro 7-9-6 is a lot different than a teaspoon of Miracle Grow 30-10-10. Under your current 5 days wet/2 days dry schedule, I’d recommend 25 ppm N. If you divide 2.3 by the %N in your formula, the result is ml/L to mix with the water. Using my two examples, that would be 2.3/7= about 1/3 ml/L for the Dyna-Gro and 2.3/30=0.08ml/L for the Miracle Grow.

As to potting it up, be aware that changing to a standard medium after having been grown in water is likely to result in some root loss, but as expensive as that root system is, it’ll probably bounce back fine.

Thank you for your detailed reply! I really appreciate it a lot as I am very much a beginner, as you can probably tell.

You recommended a 25ppm Nitrogren fertilizer under the 5 day wet regime. If I were to switch to a 1 hour wet per day regime as I think you also recommended, would I use the same fertilizer concentration? Or am I misunderstanding your recommendation?

I've been reading a lot about this, but am finding a lot of conflicting opinions, so I really appreciate your replies.

[Leafmite]

I have seen variegated Phals like this, with a thin lighter colored edging. Is it possible that it should be variegated? It actually looks okay. Do the roots turn green when they are soaked?

[miss.jakyak]

Originally Posted by Leafmite

I have seen variegated Phals like this, with a thin lighter colored edging. Is it possible that it should be variegated? It actually looks okay. Do the roots turn green when they are soaked?

That's good to know. I wouldn't have been worried, but the leaves only began to turn yellow at the edges last week, and I've had it for almost 2 years. I'm very confused because I haven't changed anything I'm doing! When the 3 long roots are wet, 2 turn green and one turns more browny green. But that has always been the case, so I'm not sure if it's a sign of a larger problem.

[Leafmite]

I agree with the rest of the advice here but if the roots are turning green, they are healthy. To me, the leaves do look variegated which is a really nice bonus. Sometimes light or other circumstances can affect variation in plants. Those that grow Vanda falcata sometimes experience plain green leaves for this reason.
Good luck with your orchid. I hope that with the great advice you have been given by the others that this will thrive for you and gift you with some lovely flowers! If you have any other questions, please ask.

[Ray]

Originally Posted by miss.jakyak

You recommended a 25ppm Nitrogren fertilizer under the 5 day wet regime. If I were to switch to a 1 hour wet per day regime as I think you also recommended, would I use the same fertilizer concentration? Or am I misunderstanding your recommendation?

Yes.

I have found, in general, that most orchids do well when getting a 75-125ppm N solution weekly, so when I "fertigate" them as often as you, I stick to 25 ppm N.