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cwallen24

Black spots and yellowing leaves on my monstera

cwallen24
2 months ago

About 3 weeks ago, the leaves/stems on my monstera started drooping. At first, I thought it might have to do with the change in watering schedule since it turned colder, and I didn't think it needed as much. I tried watering it a little more often but was afraid to let it get too soggy, so I backed off again. Well, this week, I found one leaf that was yellowing and had black spots. I checked the other leaves and didn't see any damage. I went over the entire plant to check for pests, but I didn't see any. That said, I did have a plant somewhat near this one that I had to quarantine due to thrips. I wasn't sure if thrips could cause this damage, so I went ahead and treated it a couple of times with insecticidal soap. Unfortunately, that hasn't helped, and I'm at a loss as to what to do next.

Any advice is much appreciated!





Comments (7)

  • tapla (mid-Michigan, USDA z5b-6a)
    2 months ago

    Does the pot have a drain hole? Is there a collection saucer and is the plant allowed to remain sitting in the water that exits the drain hole? By what metric do you determine when it's time to water the plant? What have you been doing insofar as regular nutritional supplementation (fertilizer)?

    Some of what looks like mechanical injury (like a bruise/ cut to humans) might be attributable to a Ca deficiency caused by over-watering, or possibly the leaf unfurling when RH levels were very low, which caused the leaf to stick to itself. If you answer the questions it will provide additional insight and perhaps lead to a more definitive diagnosis.

    Al

  • cwallen24
    Original Author
    2 months ago
    last modified: 2 months ago

    Thank you for the reply! The pot has a couple of drain holes and it seems to drain well. There is a saucer under it, but the pot is elevated on a stand and the saucer is below the stand. I included a picture with the stand/saucer for reference.


    Because I'm incredibly paranoid about overwatering, I have a few metrics I use before I water. First, I check the soil with my water meter. If that reads dry, I stick my finger down a couple of inches into the soil. Since this is a bigger pot, I'll also try to pick it up and see how heavy it feels.


    As for the comment regarding damage during unfurling. This leaf was completely normal before this all started and was in good shape when it unfurled.


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  • tapla (mid-Michigan, USDA z5b-6a)
    2 months ago


    Does your home make use of an ionic exchange water softener - one that has to be filled with salt from time to time?

    "Water meters" don't measure moisture levels, they measure electrical conductivity. To confirm, clean the probe , add a bit of distilled water to a clean cup and test. Note that it reads "DRY". Add a light sprinkle of table salt which provides the ions needed for conductivity, and you'll see the needle move to "WET".

    I'll leave info below about making/ using a wooden tell, as very useful tool for determining appropriate watering intervals.

    I suspect the issue is related to a 2-pronged issue, an overly water-retentive grow medium and watering intervals too short. Too much water = an insufficient amount of oxygen in the grow medium, which limits Ca(lcium) uptake. The plant cannot move Calcium from place to place within the plant, like it can nitrogen, phosphorous, potassium, and magnesium, Ca must be present in the nutrient stream at all times if cells are to form normally. A deficiency of Ca causes cells walls to be weak or to form incompletely. This results in the dissolution of the cells and imperfectly formed tissue, thus the holes and tears inside of the leaf margins nearer to the mid-vein of the leaf. The spoiled foliage at leaf margins are also likely the result of too much water in the grow medium, inhibiting efficient movement of water to the plant's most distal parts - leaf margins and/ or leaf tips.

    That is what I suspect, but you didn't answer the question re fertilizer. If you haven't been fertilizing, the plant will rob any/ all of the mobile nutrients listed above from existing foliage to use as the building blocks for new leaves as they occur. This process is called resorption, and it is the first step in the process of shedding leaves.

    My suggestion is to get to a place where you can be sure watering intervals are appropriate; and, if you aren't fertilizing regularly, let's start a discussion about how to put a plan in place that ensures the plant's nutritional needs are met while giving you full control. In conventional container culture, the grow medium should be all about structure, it's ability to retain that structure for the intervals between full repots, and it's ability to hold volumes of air and water the plant is able to deal with. Nutrition is not the soil's job, that responsibility should be shouldered by the grower.

    I'll watch for your comments and additional input.


    Using a 'tell'

    Over-watering saps vitality and is one of the most common plant assassins, so learning to avoid it is worth the small effort. Plants make and store their own energy source – photosynthate - (sugar/glucose). Functioning roots need energy to drive their metabolic processes, and in order to get it, they use oxygen to burn (oxidize) their food. From this, we can see that terrestrial plants need plenty of air (oxygen) in the soil to drive root function. Many off-the-shelf soils hold too much water and not enough air to support the kind of root health most growers would like to see; and, a healthy root system is a prerequisite to a healthy plant.

    Watering in small sips leads to avoid over-watering leads to a residual build-up of dissolved solids (salts) in the soil from tapwater and fertilizer solutions, which limits a plant's ability to absorb water – so watering in sips simply moves us to the other horn of a dilemma. It creates another problem that requires resolution. Better, would be to simply adopt a soil that drains well enough to allow watering to beyond the saturation point, so we're flushing the soil of accumulating dissolved solids whenever we water; this, w/o the plant being forced to pay a tax in the form of reduced vitality, due to prolong periods of soil saturation. Sometimes, though, that's not a course we can immediately steer, which makes controlling how often we water a very important factor.

    In many cases, we can judge whether or not a planting needs watering by hefting the pot. This is especially true if the pot is made from light material, like plastic, but doesn't work (as) well when the pot is made from heavier material, like clay, or when the size/weight of the pot precludes grabbing it with one hand to judge its weight and gauge the need for water.

    Fingers stuck an inch or two into the soil work ok for shallow pots, but not for deep pots. Deep pots might have 3 or more inches of soil that feels totally dry, while the lower several inches of the soil is 100% saturated. Obviously, the lack of oxygen in the root zone situation can wreak havoc with root health and cause the loss of a very notable measure of your plant's potential. Inexpensive watering meters don't even measure moisture levels, they measure electrical conductivity. Clean the tip and insert it into a cup of distilled water and witness the fact it reads 'DRY'.

    One of the most reliable methods of checking a planting's need for water is using a 'tell'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16” (75-85mm) would work better. They usually come 48” (120cm) long and can usually be cut in half and serve as a pair. Sharpen all 4 ends in a pencil sharpener and slightly blunt the tip so it's about the diameter of the head on a straight pin. Push the wooden tell deep into the soil. Don't worry, it won't harm the root system. If the plant is quite root-bound, you might need to try several places until you find one where you can push it all the way to the pot's bottom. Leave it a few seconds, then withdraw it and inspect the tip for moisture. For most plantings, withhold water until the tell comes out dry or nearly so. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue.

    Al

  • cwallen24
    Original Author
    2 months ago

    Thank you. I could be wrong, but I don't believe the issue is overwatering. I've had this monstera for over a year now and have maintained the same watering schedule with exception to the past 1-2 months where I've reduced the frequency to about once every 10 days. Over the summer months, It required watering 1-2 times a week The soil I'm using does not seem to hold much moisture. When I water it, the water quickly runs right through into the saucer. Could that be an issue?


    I have been fertilizing twice a month with a 1-1-1 fertilizer. I backed off of that once the weather turned colder though. I'd say it's been close to 5 weeks since the last time I fertilized it.

  • tapla (mid-Michigan, USDA z5b-6a)
    2 months ago

    I've had this monstera for over a year now and have maintained the same watering schedule with exception to the past 1-2 months where I've reduced the frequency to about once every 10 days. Changes in cultural conditions (light levels, relative humidity, day length, temperature, air movement, all have their impact on how much water a plant requires to carry on it's normal functions. That means watering intervals will vary significantly over the course of a growth cycle, and it's why plants are best watered on an 'as needed' basis as opposed to a schedule. The more water-retentive a medium is, the more important watering intervals are.

    Very often, as the soil column dries down, it shrinks away from the walls of the pot, leaving a gap through which water easily/ quickly flows from the upper soil surface to the bottom of the pot and out through the drain hole; all this, w/o actually wetting the grow medium. If the soil has been allowed to dry down to the point where it has become hydrophobic (water-repellent), the potential for under-watering increases significantly. If dry soil is stressful enough to cause spoiled foliage, I would expect that you would have witnessed conspicuous wilting of the leaves. Have you?

    Over the summer months, It required watering 1-2 times a week The soil I'm using does not seem to hold much moisture. That (doesn't hold much moisture) is a good thing when viewed from the plant's perspective. From my personal perspective, if a planting can stay hydrated for longer than 3 days w/o water, I know I am leaving potential in terms of growth rate, vitality (health), the plant's ability to defend itself, and eye appeal lying on the table.

    When I water it, the water quickly runs right through into the saucer. Could that be an issue? Yes, and I touched on it above.

    I have been fertilizing twice a month with a 1-1-1 fertilizer. I backed off of that once the weather turned colder though. I'd say it's been close to 5 weeks since the last time I fertilized it. Answers to the questions I asked upthread would allow me to eliminate most of what isn't causing the issue and allow us to focus on what does have the potential to be causal. W/o the answers, I can only list for you what conditions can cause the type of damage presented by your plant. Fertilizing twice/ month is about right for a plant growing outdoors in good light, but could a bit much for a plant indoors at this time of year, but that depends on what you are using and the strength of the solution. IF you are truly flushing the grow medium when you water, and are using a soluble synthetic fertilizer like 20-20-20, fertilizing with production strength solutions about every 3rd or 4th watering in summer and every 4th or 5th in winter is about right. If you're not flushing the soil, salts from tapwater and fertilizer solutions will build up in the soil and can definitely cause the type of damage presented by your plant.

    Al

  • Michele Rossi
    last month
    last modified: last month

    @tapla (mid-Michigan, USDA z5b-6a), two question for you.

    1. Don't you agree with those who say that you don't fertilize in winter because the plant slows down its growth?

    2. https://www.amazon.it/Compo-Concimi-Liquidi-Piante-Verdi/dp/B00RD30KOS I use this fertilizerin (in the second photo you can see the composition) because it is the one closest here in Italy to the 3:1:2 ratio which you consider the best. The manufacturer recommends watering every 2 weeks. Obviously this is meaningless because the frequency with which it is watered must be considered. In Italian forums, people often recommend using halved doses and at long intervals, regardless of the fertilizer (e.g. every 2 months). Instead, I watered with the dose indicated by the manufacturer (12 ml in 2 liters of water) every 3 waterings. Since I read some of your posts, I've been watering every time but adding just 2 ml to 2 litres of water. What do you think?

  • tapla (mid-Michigan, USDA z5b-6a)
    last month

    Don't you agree with those who say that you don't fertilize in winter because the plant slows down its growth? If you're asking about the statement "Plants shouldn't be fertilized in winter because growth slows", I'd have to disagree because it's too broad. If you were to say "temperate deciduous trees shouldn't be fertilized in winter" I could agree, but conifers and broadleaf evergreens don't go dormant, nor do houseplants. Plants use nutrients as the building blocks to create growth, but they also use nutrients for metabolic processes and to produce chemicals that allow them to keep their systems orderly and defend themselves.

    Houseplants slow somewhat to significantly in climes greater than 15* or so degrees latitude due to a decrease in light levels/ intensity, but they don't STOP growing. Even if the above ground organs of a houseplant seem to have stopped growing, they haven't. Even if they did stop, the roots would still be active and growing. When houseplants grow, in order to support NORMAL growth, it's essential to have all nutrients normally absorbed by the root pathway, in the medium and available for uptake at all times.

    Watering and plant usage are 2 ways nutrients are depleted from the grow medium. If a grower is watering correctly, so the grow medium is being flushed with each watering, the nutrient load after 3-5 waterings will have been largely or almost entirely depleted. At that point, the plant NEEDS fertilizer and should be fertilized. If it's neglected, growth will become abnormal, the plants systems and metabolic processes will move toward disorder, and the plant's ability to defend itself will be diminished.

    This topic can't be discussed w/o mentioning watering practices. Plants also use less water in the winter because low light slows them down. This can create the dilemma - 'should I water in small sips to avoid over-watering, or water correctly and risk the medium remaining saturated for extended periods and thereby jeopardizing root function, or worse, root function and health?'

    The dilemma above is where the advice to never fertilize houseplants in winter comes from, along with the assumption the grower will be using a water-retentive medium. The reasoning goes, "It's better to water in sips and stave off depressed root function or root diseases than to water correctly and take the risk. That, is choosing the lesser of 2 evils, which is still an evil. The correct course is, choose neither horn of that dilemma. Make sure you use a grow medium that allows you to water correctly w/o your plants paying an 'over-watering tax' (poor root function/ health). A medium that forces the grower to water in small sips w/o ever flushing the medium ensures the salts from tapwater and fertilizer solutions will collect and build in the soil. This limits water and nutrient uptake and leads to a LOT of spoiled/ damaged foliage. It also causes the ratio of nutrients in the medium to become badly skewed - especially so if the ratio of the fertilizer being used is far from the ratio at which the plant actually takes up nutrients. 3:1:2 RATIO fertilizers like 24-8-16, 12-4-8, and Foliage-Pro 9-3-6 are good choices with the FP 9-3-6 being the superior of that triad by far.

    If we have a warehouse to hold materials for building cars, but we have to order an equal measure (number) of steering wheels, tires, and headlights, how long will it be before the warehouse is so full of steering wheels and headlights there is no room for tires? That's what happens to fertilizer ratios when we don't flush the soil of even minor accumulations regularly.

    Finally, it makes much more sense to tie the frequency with which we fertilize to the frequency with which we water - as opposed to the calendar. Flushing the soil is necessary if we are to maximize vitality, but it depletes the nutrient load. You can fertilize in winter at about the same frequency as in summer, perhaps a little less. When you water, drop a marble/ button, or other object in the pot to keep track of how many times you've watered. Fertilize about every 4th watering in summer and every 5th in winter.

    IT WILL NOT HARM YOUR PLANT to have an appropriate level of fertility in the medium at all times, even during winter. Your plants will appreciate your consideration.

    Obviously this is meaningless because the frequency with which it is watered must be considered. I touched on this above, not realizing you would ask the question. You are correct.

    In Italian forums, people often recommend using halved doses and at long intervals, regardless of the fertilizer (e.g. every 2 months). Instead, I watered with the dose indicated by the manufacturer (12 ml in 2 liters of water) every 3 waterings. Since I read some of your posts, I've been watering every time but adding just 2 ml to 2 litres of water. What do you think? There is plenty of credible evidence that plants do best when nutrients are in the soil solution at a specific concentration. This means half doses or doubled intervals are always going to ensure a fertility level lower than optimum if you are watering appropriately. If you're not flushing the grow medium, it turns the whole nutritional supplementation program pretty much into a hit or miss crap shoot.

    Plants don't vary nearly as much in the ratio at which they take up nutrients, which is why 3:1:2 ratios are a good choice. They come very close to supplying about 6x as much N as P and 3/5 as much K as N ...... and that is approximately how the macro nutrients are taken up as a function of N. Plants DO, however, vary significantly in the o/a amount of nutrients they take up and what the ideal level of nutrients (TDS/ EC) in the soil might be. That (ideal concentration) varies by plant and I don't even try to pay attention to it. If I was in the business of bringing nursery/ greenhouse crops to market, I definitely would because I would have to; but, as much as I love growing plants and working hard to keep them healthy, that's a bridge too far for me as a hobby grower. I do know anyone can predictably grow a wide variety of plants and keep them ALL very healthy by nothing more than getting a few simple basics right. I struggled just like everyone else likely did. For me, the transformational point came when I got to a place where I no longer had to battle the grow media I was using for control over my plants vitality. Get the soil right and watering/fertilizing becomes monkey-easy. Then, all there is to worry about is the right light and things like temperature and other influences governed by common sense.

    Growing things is different for everyone, and we all order our priorities differently, then we make compromises that mesh with our priorities.

    Al