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yellow spotting on leaves

6 Common Causes for Yellowing Leaves on Houseplants

Watering, Nutrients, Wiruses and More

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Yellowing leaves on your houseplants can be caused by a number of conditions. Sometimes the cause is obvious, which means that you can diagnose and fix it immediately. There are other times when the problem is more of a mystery. In these cases, you’ll need to try changing one thing at a time until you see improvement in your plant.

Even after you correct the problem, it’s still likely that the yellow leaves will fall off with time. Don’t worry, if the plant regains its health, it’s possible that new leaves will fill in during the next growing season. Growing plants is always a matter of patience. Do your best to eliminate these common reasons for yellowing leaves, then wait to see what happens.

Moisture Stress

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The Spruce / Krystal Slagle

Overwatering or underwatering are the most common culprits when a plant’s leaves turn yellow.   With potted plants, it is crucial that you only water as much as the plant needs.

If you have a plant with yellow leaves, check the soil in the pot. Is it dry? Is it soaked?

If plants don’t receive enough water, they drop leaves to prevent transpiration (essentially, a plant’s way of sweating) to conserve water. Before they drop, though, the leaves will typically turn yellow. If the soil is dry and this is happening, make it a point to get the plant on a regular watering schedule.

Too much water can be just as damaging to leaves. When the soil doesn’t drain well, an overdose of water leaves the soil waterlogged and root systems can literally drown. Without oxygen, roots start to die.

Normal Aging

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As many plants age, the lower leaves will turn yellow and drop off. This is simply a normal part of their growth.

In this case, don’t worry. If the plant becomes too leggy, consider trimming back the main stem to promote new growth and bushiness.

Cold Draft

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The Spruce / Krystal Slagle

Cold drafts on tropical plants will often cause the leaves to turn yellow and drop.   This is different from short periods of exposure to intense cold, which will cause outright browning on the foliage or pale, transparent spots to appear between veins.

If your plant is near an air-conditioner vent in summer or a drafty window in winter, move it to a less turbulent place. Keep an eye on it to see if the yellow leaves spread any further. It’s also a good idea to mist tropicals that you’re overwintering to increase the humidity.

Lack of Light

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Plants that receive too little light will often start to yellow on the lower leaves before those leaves drop. If this is your issue, there is a clue that you can look for.

A plant that is yellowing from a lack of light will typically yellow on the side that is away from the light source. The leaves near the window, for instance, are getting all the light and blocking the opposite side. A great way to remedy this is to turn the pot a bit once a week, so all sides have access to natural light.

If this is the case, move the plant to a sunnier location and see how it does. If window light is tough to come by in your home—especially in winter—you might need to rig up an artificial plant light or two.

Nutrient Deficiency

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Plant leaves may also turn yellow if a plant is not receiving all of the nutrients it requires. This can be caused by too much calcium in the water if you’re using hard water or by a nitrogen deficiency.  

If this is the problem, the plant’s top leaves may be the first to go yellow. In other cases, you might notice an unusual pattern to the yellowing. For instance, the veins may remain dark while the tissue between them turns yellow.

The nutrients a plant requires vary based on the species and some are pickier than others. It’s important to try and diagnose the problem properly or you might kill a plant that can otherwise be brought back to health. It can be a good investment to purchase a small soil kit for at-home soil tests. Being able to accurately pinpoint the needs of your plant will greatly help. This will help keep your plants happy and healthy.

Viral Infection

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If your plant has a viral infection, it might show up as blotchy, spreading yellow patches on leaves throughout the plant. This may be accompanied by deformed leaves and stems, as well as discolored flowers.

Viral infections in plants may not be able to be cured and can infect all susceptible plants nearby.   As soon as a sick plant is noticed quarantine it from the rest of your plants. Check the neighboring plants to ensure the spread is contained. You can take steps to save the plant, but you must first attempt to identify the virus. Some remedies can involve fungicides, while others may require removing healthy parts and propagating. While it may be painful if it’s a favorite, you may have to discard any plants that you cannot bring back to health. Wash and sterilize any pruning tools or pots before using on other plants.

Overwatering. Missouri Botanical Garden, 2020

Perry, L. Why Houseplants Drop Leaves. University of Vermont Department of Plant and Soil Science

Hosack, P and Miller, L. Preventing and Managing Plant Diseases. University of Missouri Extension

Houseplant leaves turn yellow for a number of reasons but with proper attention and care the plant can often be saved.

Leaf Septoria / Yellow Leaf Spot

Stop Leaf Septoria (Yellow Leaf Spot) in Its Tracks!

Sometimes called “yellow leaf spot” or “leaf septoria,” this condition is caused by a fungus (or sometimes a bacteria) that attacks cannabis plants and usually appears in warm, wet weather. The symptoms first appear on the bottom leaves of the plant.

The spots may have darkened borders and may have a hard growth in the middle like a little pimple, but the thing that makes the spots the most unique is they are often very uniform, like little circles. Each spot is the receptacle of a spore (ewwww) which look like tiny dark specks in the center of each spot.

Although the spots often appear yellow like in the picture below, they will start turning brown over time. So if you see round brown spots on your cannabis leaves it could also be caused by leaf septoria.

Solution to Leaf Septoria

This fungus spores may stay in the soil over the winter, and attack your plants in the summer. Spores are also easily spread by wind and rain.

  • Immediately (and carefully) remove all affected leaves to get rid of as many spores as possible.
  • Prune any leafy parts of the plant to improve circulation through the plant
  • Avoid getting water on the leaves or laying on top of each other – you want to avoid moisture
  • Make sure to keep the ground under your plant clean. Rake away all leaves and vegetation. Adding mulch can also help prevent spores from spreading.
  • Keep plants healthy, sicks plants are much more susceptible to leaf septoria than healthy plants
  • One way to help prevent this fungus from attacking your plants is to rotate crop sites or move to a new location every year.
  • A copper based fungicide or a broad spectrum fungicide may be effective at stopping the fungus from spreading though they are best used as a preventative.
  • Depending on exactly what’s causing your leaf spot, Neem Oil may be used to help combat the problem. Neem Oil will leave an unpleasant taste/smell on buds when used to treat flowering plants, so don’t let this stuff get near your buds! You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray all the leaves evenly, since neem oil and water can separate easily. Try spraying just a small part of the plant and see how it reacts first before spraying the whole thing.

Yellow or brown round spots appearing on leaves and spreading? This Yellow Leaf Spot aka Leaf Septoria fungus can attack your plants, learn what to do!