Yellowing leaves on Monstera, Philodendron, Anthurium

[Ale_V]

Hello everyone,

I am quite new to this forum so I hope I post this in the correct section...

I'm looking for advice because many of the plants I keep in my "greenhouse" (a small room without windows, only artificial light) have leaves with yellow edges that often dry out and turn brown.

Most of the plants are Monstera (I’ve attached several photos) that I grow on moss poles, as well as some Philodendrons. The biggest issues are definitely with the Monstera. Recently, even one of my Anthuriums has shown this issue, but on one of the newer leaves.

The yellowing pattern is always the same: the edges of the leaves start to yellow and then move toward the center, turning brown and crispy as they worsen. It always begins with the leaves closest to the base of the plant and then progresses upward along the stem.

I started growing these plants 10 months ago, from small plants about 5 cm tall. Some have now reached 3 meters, others around 2. In some cases, I’ve performed the usual operation of cutting the moss pole in two and repotting the lower part to allow the plant to continue growing on a new section of pole. Often, in these cases, the leaves near the base start yellowing within 1-2 weeks, even though the plant is perfectly rooted into the moss pole itself.

As for the greenhouse conditions, the daytime temperature is around 25°C, dropping to 23°C at night, with a humidity level of around 90%. I’ve attached a precise graph from the past week (the drop in humidity in the graph is because I had to leave the door open for a bit to water the plants.)

Ventilation is provided by four 120mm PC fans placed in various areas of the room, running 24/7 to keep the air in constant gentle movement.

The light is artificial, coming from 4 LED panels (3000/5000K + IR + UV + Deep Red), positioned at various heights to keep the light as even as possible. The lights are on for 12 hours a day, with a range from 7200 Lux (128.3 μmol/s/m² —> 5.53 DLI) down to 1300 Lux (23.17 μmol/s/m² —> 1 DLI), with the plants arranged according to their needs. Beyond these light levels, the plants start to lower their leaves.

I water about once a week using only RO water with:
* Plagron "Silic Rock" (NPK 1.5 - 0 - 1.7) 1ml/L;
* Plagron "Ph Plus" (to adjust the acidity of the Silic Rock), as needed;
* Plagron Terra Grow (NPK 3 -1 - 3) 5ml/L;
* Plagron CalMag (NPK 5 - 0 - 0) 1ml/L.
* Additionally, once a month I add 1ml/L of iron to the solution.

The substrate in the pots is a mix of:
* Coco Bark -> 1
* Classic Orchid Bark 6/9mm -> 1.2
* Pumice 6/9mm -> 1
* Zeolite 6/9mm -> 1
* Fine Vermiculite -> 0.5
* Perlite -> 1
* Coco Coir Powder -> 0.5

I've tried everything I can think of to figure out what the issue could be, but I'm still stumped. If anyone has any ideas… I’d be grateful for any advice!
Thanks!

[Ray]

What is your water chemistry? Do you need the cal-mag, or are they already in the water?

Why do you add silicon? About the only plants that absolutely NEED it are grains like rice.

Between the three fertilizers you listed, you're applying about 260 ppm N weekly, which seems to be about double what I'd use.

Are the media components, especially coir based, well cleaned before use? Coir products are known to contain high levels of sodium.

[Ale_V]

Hello and thank you for your answer!

For water, I use reverse osmosis water from my system. Fresh, it has a pH of 6.5, which rises to 6.8 after it sits in my tanks for a while. My (non-professional) instrument shows a reading of 5 ppm before I add anything to it.

When I started, I adjusted the water pH to 5.5, but after a month I noticed this was likely too low, as the leaves developed deformities. Now, I balance the water to 6.5 pH, even though online and in books I see recommendations suggesting 5.0 to 6.0 pH for aroids.

I've attached four technical sheets from the manufacturer for the products I use. I was applying a high amount of fertilizer based on the manufacturer’s suggested dose and online sources indicating that Monstera TDS should be around 1500 ppm (not N ppm). This level was achievable with the amount of fertilizer I was using.

I began using silic rock on the recommendation of a shop assistant where I bought the products. I wasn’t aware it was primarily for grains, and honestly, it’s quite inconvenient because it keeps lowering the pH. I guess I should remove it completely...?

For coco coir, I purchase from a reputable producer who states that it’s washed and has a verified EC. I haven’t personally tested it, though.

Thank you very much!


Ale

[estación seca]

It appears none of the fertilizers contains micronutrients.

Yellowing then browning of leaf edges can be caused by potassium deficiency.

I think Ray was asking about the pH of the mixed solution. Measure the effluent water from a pot. It may be very different from what you apply.

[Leafmite]

My opinion: The yellowing looks to me like some nutrient imbalance. I would check your pH. Most tropical plants like a lower pH. If these were my plants, I would probably first flush the pots well under running water, then add some Ironite, a tiny bit of bone meal, and my newest addition to the fertilizer arsenal, cottonseed meal. The Ironite and Cottonseed meal are among the many fertilizers that lower the pH slightly without burning the roots and causing further stress to the plant while it recovers. I always like to give my plants a Calcium source as all plants need Calcium. I also have a slow release fertilizer that has all of the micronutrients (the weird stuff).
Good luck!

[rbarata]

I have been experiencing this issue for years with a Monstera and I noticed that it starts in spring, when temp increases. Spring here has temp around 25°C on average. In the colder months, the plant is fine and growing.

[Ray]

1500 ppm TDS is not outrageous, but ppm N is a better control factor. Think of it as "counting calories" as opposed to the size of the total meal.

The pH of the applied solution really isn't as critical as the rhizosphere pH, and that is controlled far more by the plant and the medium.

You can prove that to yourself by evaluating the "pour through" pH:

1. Apply your nutrient solution.
2. Wait 30 minutes for the medium to fully drain and for the rhizosphere chemistry to equilibrate.
3. Slowly trickle just enough pure water (RO is fine) over the surface of the medium to collect about 50 ml of drainage from the bottom.

Test the pH of that, as it will tell you what's happening in the pot. Do the same with a different solution and the result will be remarkably similar.

[Ale_V]

Thank you everyone for your suggestions!

I don't think the issue is with the pH to be honest.
I've tried pretty much all the possible ranges, starting at 6 pH, lowering it down to 5.5 pH (and that's when I've got the deformed leaves I talked about - I attach some images here of my Monstera Siltepecana and Adansonii).

I think it could be either: not enough nutrients (even if I would be surprised) or too much.
From my point of view it would make sense either cases as if it was not enough the plants would drain resources from their older leaves in order to support the newest one, if it was too much it would maybe create these sort of burns. I don't know...

Reading online it seems like these plants wants a lot of fertilizer, especially when they grow bigger, but no where people are as tecnical as you as a community when it comes to orchids.

It's impossible (at least I couldn't find it) to find a range of N ppm for Aroids, I've just found a couple of website stating the TDS for Monstera alongside with peppers and tomatoes...

I'll try to do the analisys as Ray suggest on different pots and I'll let you know the results! But how to interpret them?

Thanks a lot!!!

[Ray]

Something more to throw into your thinking:

For ANY plant to add ~500 g of mass - certainly faster for the monstera than a paph, for example - it must absorb and process about 5 grams of NPK and about 100 kg of water. Then, if you add the fact that plants lose as much as 95% of their absorbed water through transpiration, it means the plant must actually take up as much as 2 tons of water to gain that 1/2 kg!

[Ale_V]

Sorry for being absent – I've had a pretty intense few days of work. Yesterday, I finally got around to watering my plants, and I took the opportunity to do some water testing as well.
Here’s the process I followed to prep the nutrient solution:
Pure RO water: pH 6.16 | TDS 3ppm
Added CalMag: pH 5.63 | TDS 282ppm
Added Terra Grow (fertilizer): pH 5.37 | TDS 774ppm
Added pH Plus (about 6ml): pH 6.48 | TDS 793ppm

Following Ray’s instructions, I checked the runoff water from the pots about half an hour after watering them with this solution. Here’s what I found with different plants (I'll test more in the future):

Alocasia Dragon Scale: pH 4.37 | TDS 821ppm
The plant seems really happy and is growing beautifully.

Philodendron Rubrijuvenile: pH 3.84 | TDS 2470ppm

There’s some yellowing at the edges, and a few months ago, it branched on its own, as if the main tip had died and it started sprouting from lower nodes.

Philodendron Splendid: pH 3.86 | TDS 2470ppm

Similar branching as above, but without the yellowing. Now it has four branches growing vigorously off the main stem.

Philodendron Verrucosum: pH 5.85 | TDS 1590ppm

This one's a bit of a problem child. I bought it about 8 months ago along with other plants of the same size (around 5 cm), and it’s barely 12 cm tall now – it just doesn’t want to grow. Meanwhile, the Monstera Esqueleto has shot up to 2.5 meters from the same starting height, with the same substrate and water.

I’m no chemist, and I don’t quite know how to interpret all these results, but it feels like something is really off…
It seems like there’s a significant salt buildup I guess.

Am I right in thinking I should flush everything with RO water and start from scratch? How shall I prepare the solutions not to incur in this problem again?
Thanks a ton for any help!

P.S. Ray, I’ve been mulling over your last post (super interesting!), but I can’t quite see how it connects with what we were discussing before. Any extra hints?