If you’re a new plant parent, it’s easy to worry about every new thing that’s happening with your green babies. So when you see a yellow leaf at the bottom of your plant, it’s totally understandable if you freak out a little.
Is it root rot? Nutrient deficiency? Sun burn? Not enough water? Some sort of disease? Someone please tell me my green child is going to live!!
The TL;DR of this story is that one or two yellow leaves on the bottom of your growing happy plant is perfectly normal and there’s probably nothing to worry about. As plant leaves get old and less effective, the plant may decide that the leaf is not pulling its weight so it’s time to go. Or larger new leaves may be shading out the lower leaves. Less light means less photosynthesis. That makes shaded leaves a potential energy drain instead of an energy maker, so the plant will shed them.
Those processes are perfectly normal. If only one or two leaves has turned yellow, the plant is otherwise healthy and growing, and you don’t see any signs of pests, there’s probably nothing wrong with your plant. She’s just growing up.
If your plant is showing other signs of stress though, there may be more to the story.
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Why Plant Leaves Yellow At All
Plants know when something is wrong. If a leaf is damaged, diseased, or otherwise stressed, the plant may decide to abort that leaf. Or the leaf might just be old and less effective than it used to be.
The first step to a plant dropping a leaf is re-absorbing nutrients like magnesium, and that’s usually what’s actually making the leaf turn yellow. Broadly speaking, if the leaf isn’t yellow because it’s old, it’s turning yellow for one of the following reasons: damage, disease, not getting enough light, or not getting enough water or nutrients. You’ll need to do a little investigating to diagnose the specific problem.
As a side note – I recommend not cutting leaves off of plants until they’re yellow/dried up to give the plant time to re-absorb nutrients. According to plant guru Al Tapla (who you can find doling out excellent plant advice on various plant forums), reabsorbing nutrients before a plant sheds a leaf is “a key strategy which allows plants to avoid losing nutrients they already paid for”.
Exceptions I make for this rule are while controlling pests or a spreading disease like bacterial rot. Then those leaves may have to go ASAP. I do sometimes cut off yellow leaves before they’re fully dry for aesthetic reasons too, but only on otherwise healthy plants.
OK, back to the diagnosis. Your plant knows something is wrong, and it’s yellowing and/or dropping leaves. Why might that be?
Let’s unpack those categories of problems I mentioned earlier, and talk about some ways to check for, and correct those problems.
The Leaf Is Physically Damaged
Damage could come from all sorts of things. A nibbling cat, pests like spider mites, thrips, scale, or mealybugs, or even sunburn. Plants can’t regenerate dead leaf tissue, so once a part of a leaf is torn, burned, chewed, or eaten, it won’t turn green again. No green means no photosynthesis. If there’s enough damage to a leaf for whatever reason, the plant may decide the leaf isn’t worth keeping.
Look for evidence of physical damage to your plant. You can often see actual pests on your plants, though they may be tiny or setting up shop under the leaves or in hard to see nooks and crannies. Summer Rain Oaks has a really nice write-up on identifying common houseplant pests.
Leaves that have pale, bleached, or dried up brown patches may have sunburn. If you’ve recently moved a plant into a sunnier spot this is a possible cause for yellowing or burned leaves.
Torn leaves are usually caused by larger beasts such as a pet, or even you. Could your cat have chewed on the leaf? Were you a little rough with it when re-potting? Consider anything that might have actually physically ripped the leaf.
The fix for damaged leaves is removing the thing that’s damaging them. If you find pests, you’ll want to come up with a plan for eliminating them through beneficial insects, organic pest control, mechanical removal, or homemade pest spray options. If your leaves look sunburned, pull the plant back from the light source. If your cat is chewing your green babies, send your cat to me and I’ll take care of her :)
The Leaf Is Diseased
Did you know plants can get viruses? Weird but true. A common kind of plant virus is called a mosaic virus. There are lots of mosaic viruses, but a typical sign is yellowing or pale leaves in a particular lacy or splotchy pattern (hence the name ‘mosaic’).
Interesting But Unnecessary Side Note: Not all mosaic viruses will kill a plant. In fact, some viruses are used deliberately to introduce variegation into a plant. During Holland’s tulip mania which reached its peak in 1637, the most expensive tulip in the world – Semper Augustus – was advertised for 13,000 florins, the price of a nice house. It was later discovered that the beautiful pattern on these tulips was caused by a form of mosaic virus.
But even when they are deliberately introduced viruses often weaken the plant, meaning it may not live as long, and they may be more susceptible to other problems in the long run. And the viruses you’ll typically get accidentally are not ones that make a plant beautiful anyway. So don’t try to give your Monstera deliciosa a virus, it’s not going to turn it into a M. deliciosa variegata.
If you suspect your plant may have a virus, do a search for “[name of your plant] virus” to see if your yellow or mottled leaves look like the pattern typical of a virus on your plant species (different plants get different viruses and they don’t all look the same).
If you think your plant does have a virus, you might decide to get rid of it since there are no cures for plant viruses and they can spread to other plants in your collection.
Other Plant Diseases
Other diseases typically include fungal or bacterial disease ie rot. These are typically caused by environmental factors – usually too much water and/or not enough air flow. We’ll talk about root rot specifically when we get to the watering section. But signs of fungal infection or leaf rot include leaf spots with a yellow halo, or leaf spots that appear water soaked or mushy. You might also see powdery white coating on leaves which indicates another type of fungal infection.
The fix is usually to remove infected leaves so the bacteria or fungus doesn’t spread, and to correct the environmental problems by increasing air flow, and making sure water doesn’t sit on leaves. You can also use houseplant fungicides or a homemade solution to reduce or prevent certain diseases like powdery mildew.
The Leaf Is Not Getting The Right Light
Remember how we talked about lower leaves turning yellow because they’re being shaded out by newer, bigger leaves? The same thing can happen to any leaves that aren’t getting enough light for any reason.
Maybe you moved the plant to a corner you thought was bright enough. Maybe there’s a plant in the window that grew a ton this summer and now it’s blocking the light from the rest of your green kids. Or maybe you forgot to rotate the plant and the side facing away from the light is getting light starved.
I recently moved a Monstera adansonii from a bright spot in my home to a place I thought was equally bright. But I didn’t think about the stack of books that was directly between the plant and the light coming from the window. After about a week, I saw some major yellowing of leaves, all focused on the side of the plant that was getting shaded by the books. I moved the plant to an un-shaded spot, trimmed the yellow leaves, and she’s doing much better. Lesson learned.
If you see yellow leaves focused on one side of a plant, or yellow leaves that are on the inner part of the plant (getting shaded out by outer leaves) lighting might be your issue. It’s also possible that lighting is a problem if you see yellow leaves all over, though the darkest side of the plant, along with the bottom or inner leaves will probably show the problem first.
To stop the problem, you’ll need to add light. Either move the plant to a brighter spot or add a lamp or grow light to the shady side of the plant. In less extreme cases just remembering to rotate the plant every few days can help even out the amount of light the leaves are getting.
The Leaf Is Not Getting Enough Water (Under & Over Watering)
You might be surprised that the leaf not getting enough water can be caused by under watering and over watering. Under watering is obvious, but over watering can cause root rot. Rotting roots can’t deliver water to the plant, so you’ll get similar symptoms for both over and under watering (at least at first).
Another cause of inadequate water is physically disturbed roots. Repotting into new soil can damage roots and make a plant sulk. And pests like grubs can eat roots and make the plant less able to absorb water.
Signs of inadequate water include drooping, wilting, or drying leaves. Leaves may turn yellow, especially near the bottom of the plant.
You may also see large brown crispy patches develop on the inner parts of the leaves. This can be caused by edema (also spelled oedema) – or swelling and bursting of the leaf tissue when the plant is kept too wet. Or it can be from under watering and the plant not being able to provide water and nutrients to that section of the leaf.
If you recently repotted a plant, and drooping or yellow leaves is a new problem, you might have disturbed too many roots. But if you haven’t repotted, investigate the other causes.
How to Check Soil for Too Much or Too Little Water
Push a finger two inches into the plant’s soil. If it’s totally dry it’s probably time to water. Many dehydrated plants will perk right up after a good drink, but you may have to do some work to get the soil moist again since really dry potting mix can actually start to repel water. Try soaking the whole pot for a few minutes in a sink or container to get it back to normal, then let it drain thoroughly.
If the soil is obviously wet you’ll want to look at the roots to check for rot.
Gently pop the plant out of her pot and take a look at the roots. Healthy roots are typically firm and white. Brown is OK as long as they’re firm. If they’re mushy, slimy, or smell bad, you’ve got rot. Remove the rotten roots, consider replacing the soil with a more well draining mix, and place the plant back in her pot.
While you’re in there, look for signs of grubs or other pests. If you find fat white grubs, centipedes, snails, or other bugs, you may want to repot the plant into fresh soil. You can also try a hydrogen peroxide treatment on the roots before you re-plant to get rid of pest eggs.
For all of these cases, make sure to water the pot when the top inch or two of soil is dry, and not before (for most plants). If the plant is in a large pot or a very water retentive mix, use a bamboo skewer inserted deep into the soil -like a cake tester- to see if the soil at the bottom of the pot is still damp.
You can also use a moisture meter – but know that those don’t really measure moisture. They measure electrical conductivity as a proxy for moisture. Using distilled or highly purified water could cause it to read much dryer than it is, using fertilizer or softened water could cause it to read wetter than it is.
You might also want to reduce the light she’s getting just a little for the first week or until she recovers. And don’t fertilize during that time either. High light and fertilizer can encourage new foliage growth, and your plant needs to compose herself and regain her energy before she starts pushing out new leaves again.
The Leaf Is Not Getting The Right Nutrients
Just like people, plants can suffer when they’re getting either too many, or not enough nutrients.
Not Enough Nutrients
Low magnesium levels, iron levels, nitrogen, or calcium levels, and others can all cause yellowing of plant leaves. Typical signs include specific patterns of yellowing, browning, or leaves turning very light green. Leaf veins may stay green.
Signs can vary between different nutrients, and between different plant species. There are lots of general guides for diagnosing nutrient deficiency in plants like this one from The University of Arizona. But the best way to diagnose the problem is probably to google “[your plant name] nutrient deficiency”. Look for images that match the yellowing pattern on your plants leaves.
Remember that when a leaf is going to drop, the plant will reabsorb nutrients from that leaf including magnesium. That means other kinds of damage can look a little like magnesium deficiency at first. But where lighting or other issues will typically effect a certain area, nutrient deficiency may seen across a broad group of leaves.
Compare my sad adansonii to the picture of nutrient deficiency above. Low lighting caused a few leaves on one side to yellow at different rates, whereas the nutrient deficiency photo above shows a mass of leaves all suffering equally.
To clear up a deficiency, add the missing nutrient in a form the plant can absorb. For example, magnesium deficiency can be corrected with a foliar spray of epsom salt (magnesium sulfate) solution. To prevent future problems, fertilize “weakly weekly” (half or quarter strength, every time you water), with something like DynaGro Foliage Pro which contains all of the macro and micro nutrients most houseplants need.
Too Many Nutrients
Signs of mineral build up or too much fertilizer are browning leaf edges and tips, sometimes with a yellow halo around the brown spots. This particular problem is easy to diagnose because it almost always just effects the leaf edges and/or tips. That’s because water that’s full of salts get drawn up through the roots eventually make their way to the leaves. When the water evaporates the thinnest most delicate parts of the leaf – the edges and tips – get burned by the leftover salt.
You can usually just cut these parts off. But if you want to prevent them, make sure you’re not using hard, softened, or highly chlorinated water. Most municipalities in the US use a form of chlorine that doesn’t evaporate, so leaving your water to stand overnight generally won’t help. Try using an activated carbon filter like a pitcher filter. I use one that attaches to my shower head.
And don’t go too heavy on the fertilizer. A low strength more often is usually better for plants than a high dose less frequently.
If you have signs of mineral buildup, you might want to flush the pot with clean filtered water. Totally saturate the growing medium, let it sit for 15 or 30 minutes to let the salts and minerals in the soil dissolve. Then flush the pot with water again to rinse out those excess minerals.
This is fine to do frequently if your plant is in a really well draining mix, but if it’s pretty water retentive you might need to do some work to get the excess water out after this.
Tipping the pot to a 45° angle can help drain excess water (if there are drain holes at the edges of the pot, not just the center). And setting the pot on a folded up towel can help wick away excess moisture too. Some people actually insert a long polyester cord into the bottom of their planters to help wick away excess water as well.
Hopefully the yellow leaves on your plant are just a sign that she’s growing and doesn’t need those smaller, older leaves anymore. But if it’s something more serious, I hope the information here has helped you diagnose and tackle the problem.
Get well soon plant friends!
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