Why Do Houseplants Leaves Turn Yellow


It is not uncommon to find that even after doing most of the necessary things to make your plants healthy, you may find that a few leaves begin to turn yellow or even all of the leaves. Yellowing leaves on your houseplants can be caused by a number of conditions.

Why do houseplants turn yellow? There are many reasons for this including moisture stress, lack of adequate light or the presence of excessive light, nutrient deficiency, and even insect damage. I will take you through these and provide you with solutions to your problem.

In essence, yellow leaves mean different things depending on: the plant affected and what other symptoms the plant is showing. Growing plants is an activity that requires lots of patience, so you have to eliminate these common reasons for yellowing leaves, then wait to see what happens, so you know the next step to take. This is a process of elimination.

The list below are the many reasons for yellowing leaves:

  • Moisture Stress
  • Lack of Light
  • Unwanted Insects
  • Temperature
  • Nutrient Deficiency
  • Ageing

Moisture Stress

Most people are not exactly sure how best to measure just how much water a plant needs. The most common type of stress a plant may face is the moisture stress. Overwatering or under-watering are two types of moisture stress. If your plant is under-watered, in order to prevent transpiration and conserve moisture, it will sacrifice some of its foliage (in this case, maybe its leaves). Before they drop, the leaves will typically turn yellow. When the plant is under-watered, asides from simply having yellow leaves, the plant may also curl inward, and droop or crisp. If this is the case, you will need to water the plant immediately and, as well as ensure to water it regularly.

On the other hand, if your soil is kept too wet or watered more than what may be necessary, this can have the same effect on your plant as keeping the soil too dry – in essence, dehydration. If you keep this up with the soil too for long periods of time, the plant may go through root rot, which will not allow your plants to take up water, essentially dehydrating your plants, making them can turn yellow.

It is important to regularly check just how much moisture your plant is getting. To do this, press a finger into the plant’s soil (about an inch). Make sure to go beyond the surface of the soil as it tends to dry out the fastest. If the soil is parched an inch below the surface, it’s likely your plant is thirsty. If the soil feels damp an inch below the surface, your plant may be getting enough water.

Lack of Light

A major reason your plant’s leaves are turning yellow is that they are receiving too little light from the sun. Plants that receive too little light will often start to yellow on the lower leaves before those leaves drop. Yellow leaves can also be the result of too much light.

The leaves of shade lovers such as tropical ferns, nerve plant, and  Calathea, for example, will slowly fade to yellow if they are kept in a sunny spot. On the other hand, houseplants which require sunlight such as succulents, croton, and Jade plant may start to yellow if they are grown in dim conditions.

It is typical that a plant that is yellowing from a lack of light will yellow on the side that backs the light source. This is what many plant owners do, or fail to do – not finding enough light to cover the entire plant. The leaves near the window, for instance, might then be getting all the light and blocking the opposite side.

If this is the case, you should consider moving the plant permanently to a location that receives more sunlight or let it soak up the sun near a window for a couple of hours, monitoring the plant, tracking its progress and seeing how it develops.

If window light is still not enough in your home, you might need to set up a few artificial plant lights. Try to make sure they cover the plant as optimally as possible.  Some plants are sensitive and might find it difficult to adjust, so make sure to keep laser eye focus on them. 

Unwanted Insects

Pests or unwanted insects can also cause a plant to yellow, attacking the plant inside and outside. Major types of such insects include:

  • Mites
  • Aphids
  • Mealybugs
  • Thrips
  • Scale
  • Whiteflies

These insects are often identified by the effects they have on the plants, rather than any physical identification, majorly because these insects are too small to see with the eye.

The insects primarily suck the sap of the plant, usually leaving cuts, wing remnants, patches on leaves throughout the plant, and other materials, and destroy the overall quality of the plant, resulting in yellowing. These insects may be doing more damage than simply making the leaves of the plants yellow.

If pests are present, it’s likely you’ll notice other signs of an invasion upon close inspection. There may be tiny holes on your plant, indicating that the presence of spider mites on them. There may also be fluffy white wax on your plant, showing that there are Mealybugs on the plant. 

Such unwanted insects may be taken care of in a number of ways, such as:

  • Yellow sticky traps
  • Hosing
  • Natural predators
  • Companion Planting
  • Organic Neem Oil
  • Organic SB Plant Invigorator
  • Vacuuming
  • Insecticides

Yellow Sticky Traps

These are traps that are pieces of yellow card with a double sticky side. Insects such as Aphids, Mealybugs, Whitefly, Thrips and fungus nats are all attracted to the colour yellow. These simply stick to the card and die on the card. Simply place these cards throughout your plants for the best effect.

Hosing

An effective method of dealing with these insects on outdoor plants is to simply hose them off. This knocks them to the ground and is too wet to climb back onto the plant and die.

Natural Predators

Natural predators such as ladybirds (ladybugs), Rove Bettle and even nematodes are all perfect predators to introduce to your garden. These come on little viles or tubs and can be released in a high tunnel or greenhouse. They hunt down their prey suppressing the numbers of these pests.

Companion Planting

Companion planting can help in reducing the numbers of these insects that can turn you plants leaves yellow. Planting marigold, for instance, can help stave off root-knot nematodes. Each insect that causes you a problem in the garden has a corresponding plant they don’t like. I will cover this in more detail in a future post.

Organic Neem Oil

Neem Oil has two effects within the garden. It can work as a pesticide and a fungicide. It is very effective at killing most mildews such as powdery mildew or white mold. It can also kill Aphids Mealybug and whiteflies, but this list is not exhaustive.

Neem oil is organic and comes from the pressings of the seed and leaves of the Neem plant. This plant is actually a tree and it hails from India.

Organic SB Plant Invigorator

Like Neem Oil, SB Plant Invigorator has two tasks in the garden. It is environmentally safe and works as a pesticide and a folia feed. The product is designed as a supplement to help bring plants back from the brink and return their vigor.

It is a soap-based solution, this was created to stick to the leaves to give the active ingredients time to do their work with providing the plant with the required nutrients. However, It has a side effect in that it is very effective at killing Aphids, Whiteflies, Red Spider mite and mealybugs.

Like Neem Oil it is very good at dealing with mildews and fungus too. In fact, I use both neem oil and SB Plant Invigorator as a way to treat powdery mildew when growing Giant Zucchinis. I made a detailed post about that too if it is of interest to you.

I have suffered from a lot of these insects with my plants over the years. I have found some very effective ways of treating them and I made a video showing you the 5 very best solutions to these problems. You can view that below.

Temperature

Plants need to be kept under certain conditions to be able to develop properly. If they are kept too close to a heat vent, fireplace, air conditioner or drafty window or door, they may react to what would be extreme conditions for them by their leaves turning yellow. Most houseplants thrive in temperatures between 65 and 80 degrees F.

Nutrient Deficiency

Plant leaves may also turn yellow if a plant is not receiving all of the nutrients it requires. 

In this case, the plant’s top leaves may be the first to turn yellow. In other instances, you might notice an unusual pattern to the yellowing – the veins may remain dark while the tissue between them turns yellow.

Major reasons for nutrient deficiency are under-fertilizing and over-fertilizing. People often use too much fertilizer in order to make their plants grow faster, but this may be counterproductive in that it creates an unsuitable environment which causes the leaves to burnout, thereby turning them yellow. Under-fertilizing means the plant will not receive an adequate amount of nutrients it is meant to receive, causing the plant to not have enough resources to go through a stable natural process, thereby causing the leaves to yellow.

Ageing

As plants grow and age, it is not unusual to find that the lower leaves will turn yellow and drop off. This is simply a normal part of their growth. This doesn’t mean your plant is ill, or any of the already mentioned reasons for plant yellowing is happening to the plant. It just means that those lower leaves are now being shaded by higher foliage and are no longer needed by the plant. It’s best to allow that leaf wither out itself, to make sure it undergoes the completely natural process. However, make sure this is a leaf that has been there for long.

Conclusion

It’s true that seeing yellow leaves on your plants may not be a good sign. It may mean either any of the following outlined, but do not fret. Most of them require quick fixes and are largely inexpensive to sort. Make sure to monitor how the plant reacts to whatever solution you utilize and see how effective it may be to know whether you might need to adopt another solution.

I hope you enjoyed this blog post about leaves turning yellow. I trust it answered your question fully. If this was of interest to you, why not consider checking out some of my other blog posts and subscribing to the blog so you don’t miss future content.

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Remember folks; You Reap What You Sow!

Tony O'Neill

I am Tony O'Neill, A full-time firefighter and long term gardener. I have spent most of my life gardening. From the age of 7 until the present day at 45. My goal is to use my love and knowledge of gardening to support you and to simplify the gardening process so you are more productive

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