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I have a very interesting set up and had questions about the differences across our factory floor.

We have three columns of Golden Pothos that are numbered about 96 plants (unless the irrigation failed on one and I removed the plant before it died) per column: Three Golden Pothos Column

The irrigation is set up for a hose to connect to about my chest height. The water travels through the plastic hose to the top of the column. From here the water gets distributed through regulators to each plant. There is a regulator every two rows. It's kind of a nightmare.

Previously the pots were self-watering, but we had huge issues with proper drainage and we lost almost every plant. This time we made sure each plant had a large amount of drainage. This also has the effect of the higher plants draining into the lower plants. This set up seems to work well, to ensure more even watering across the board.

However, I am regularly finding about 4 to 6 leaves that are dead per plant, about every two weeks. Is this volume normal? I know this question was asked before, but my set up is atypical. We have other plants in the area that seem to be doing much better as far as die-off is concerned. I only remove one or two leaves per two or three plants. They are also pictured:

Cart Archway

The other plants are watered by hand. I also water the columns by hand every week I don't water using the irrigation (every other week)

So why what appears to be a significant difference? What can I do to help the columned plants grow better? Is there anything that we're doing wrong?

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First of all, thank you for posting a detailed explanation and such numerous and helpful photos.

The appearance of the leaves in most of plantings is indicative of over watering and root rot.

Symptoms:

  • the leaf is a dull green rather than shiny
  • the leaf lacks turgor. The leaf is limp even though the soil appears moist.
  • it appears that the plants on the top of the columns are in better shape than the bottom

Where I work they have a "living wall" as seen here which has a similar system with water at the top and trickle down to the base. They too have had issues with the soil being too moist at the bottom which encourages root rot and spots appearing on the leaves which I believe indicate a secondary infection by some virus/bacteria.

The issues are that the plants at the bottom get more water and less light than the ones at the top. This is a horticultural challenge!

To verify my diagnosis:

  • remove a plant from the bottom row
  • take it out of the pot
  • open the root ball
  • examine the roots

New healthy roots are firm and white. Roots with rot are brown and mushy. Pot bound will have the complete perimeter of the pot covered in old,brown and firm roots.

Solutions:

  • watering by hand will work but is very time consuming
  • or do not water by schedule. Use your irrigation system only when the plants on the top are at the point of wilt and test the ones at the bottom to see that they are dry enough.
  • or only use the irrigation system on the plants that you cannot reach and water the rest by hand
  • or consider potting the plants with problems in a different way
    • the current method is to fill the planter with soil and let the pothos use the entire root mass.
    • for the problematic plants on the bottom you want them to get less water or only enough. Repot the ones with problems in four inch pots with a wicking system and let them absorb water as required. Also see here. This approach minimizes manual work and allows different amounts of moisture for each plant
  • I'll pick one out for inspection sometime today. Your information is appreciated, as it is more than I've gotten from others in the area (Phoenix). I'm not inclined to wait till the plants on the top begin to wilt, as it seems to be "too late" at that point to water, and guarantees more die off than I would like. I would hate to water the plants by hand, but it appears that some are more waxy than others, and it's highly random plant-to-plant (at least the further down you travel). What about plants that have BOTH waxy and dull leaves? – Ellocomotive Jan 10 '14 at 17:29
  • Turgidity also seems to be very random. I'll update with any discoveries soon. I'm still getting new growth on the columns anyway, so I'm not too worried. – Ellocomotive Jan 10 '14 at 17:30
  • I would hate to tear apart the plants for your third method, as I just about lost my mind over these already. Perhaps I can do it over time for suffering plants. – Ellocomotive Jan 10 '14 at 17:31
  • You have to investigate to see if I'm right. Plants with glossy and dull leaves could have some stems rotting. If it's rot the dull leaves should tend to be from stems in the middle of the pot which stays wetter longer. – kevinsky Jan 10 '14 at 17:37

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