Leaf edges turning yellow in hydroponics
 

Hi All, as the title says, I'm growing an orchid in hydroponics and the edges of its leaves are beginning to turn yellow. My cycle is 5 days in water (about 2 inches) and 2 days out of water. At the beginning of the 2 days, I put the roots in 2 inches of very dilute fertiliser.

What am I doing wrong?

Welcome.

I think it's dying. Phalaenopsis don't do well in hydroponics. The leaves are very shriveled, suggesting it's not taking up enough water. The yellowing is probably from nutritional deficiency.

I would end the experiment and put it into a pot with medium to large bark, keep warm, water and fertilize regularly.

Thank you for replying! When I rescued it, it only had 3 roots (the big ones pointing down, which I believe are air roots). Now, I think all of its roots are air roots, unless I'm wrong. When I repot it, do you think it will grow new roots into the potting medium?

When you repot, try to get as many roots into the pot as you can. Use a twirling motion to rotate them in. Use the smallest pot that holds the roots.

There is a great thread here about growing Phals. From the left yellow menu choose Forums then Beginners. Near the top look for a sticky thread, The Phal abuse stops here. Read through the first few pages.

If it has added that many roots, something is going well.

How often are you wetting the roots?

How often are you feeding it, at what concentration and with what fertilizer formula.

I agree that it's probably a nutrient deficiency, so don't overlook the fact that it is only taking up as much solution as the velamen can absorb per-dunk. If potted, it has more time to continue to absorb more.

Thanks a million! I will take a look :)

---------- Post added at 11:09 AM ---------- Previous post was at 11:02 AM ----------

Thank you for replying! 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.

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.

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.