4 Causes of Yellow Leaves

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What You'll Need
Magnifying glass
Warm water
Water hose
Spray bottle
Soft cloth
Cotton swabs
Plastic wrap
insecticidal soap
Potassium fertilizer
Used coffee grounds
Epsom salt
Agricultural lime.
Possibly—an appropriate chemical insecticide

Gardening is such a rewarding activity that can sometimes become a bit frustrating when the plants start to deteriorate without any apparent reason. When taking on such projects, you are likely to come across various problems and challenges. Most of the causes come from various diseases, pests, severe weather, or even unintentional but inappropriate care such as over or under watering, described here with some solutions for most causes on how to cure the problem.

1. Improper Watering

On a plant that lacks regular watering, the leaves eventually get yellow and fall off for lack of nutrition. The way the plant is watered is often the root of the problem. Sometimes, a plant shouldn’t be watered as often as it is, but instead more thoroughly, making sure that its roots system gets plenty of moisture—which favors a deeper growth—then repeating the process but only after the ground has started to dry.

Since the roots need oxygen to properly grow, when administered too much water, especially when the drainage of the pot is not adequate, the excess water keeps the roots soaking and eventually drowns them. The leaves then start to turn yellow and fall off.

Two Symptoms of Overwatering

A green crust on the soil’s surface is an indication of algae, which is a result of overwatering.

While repotting a plant you can check for black roots, which is an indication of decomposition of the roots. Healthy roots are white.

Corrective Steps

Make sure that your pot or container has enough of drainage and water less often waiting until the ground around it starts to dry before watering it again.

2. Extreme Weather

When a garden is at its initial stage of growing and the temperature suddenly drops through the night to give frost or extremely cold weather, it will often shock the plants and deter their normal growth. Even if the frost doesn’t touch the plant, just the cold air can affect the plants, as when a spell of extreme heat and dry weather will deteriorate the plants leaving their leaves a sick yellow appearance. Bringing them back can easily take weeks.

3. Pests

Several insects and other pests such as aphids, mealybugs, immature scales, thrips, fungus-gnat, whiteflies, and spider mites, to name a few, feed on plants and foliage. If your leaves start forming yellow spots, check them good for tiny critters (Figures 1 to 7) using a magnifying glass, especially under the leaves. You should first try to identify the type of bugs you’re dealing with, and follow the follow these steps to resolve the threat with ecofriendly solutions.

Ecofriendly Solutions

If you catch the infestation early, handpicking the bugs might be enough to clear the problem.

aphid infestation on a leaf

To get rid of aphids and mealybugs (Figures 1 and 2) you can rub the leaves they're on with a cotton swab dipped in alcohol. If only a small portion of the plant only is affected, removing only the damaged area could resolve the issue.

mealybug on leaf

Before the condition gets too severe, you can use warm water and wash the plants that have smooth leaves every couple of weeks which will often discourage the infestation. With smaller potted plants, you can wrap the soil to keep it inside the pot (with plastic wrap), then lower it into the bucket of water and rinse it lightly. A larger plant’s leaves can be showered with warm water or wiped with a wet cloth.

If the problem comes from scale insects (Figure 3), unless the infestation is already advanced, they can be scraped off with your fingernail.

scale bugs on a leaf

If the plant is sturdy enough, you can spray all its surfaces with water to remove any pests, especially to control spider mites (Figure 4) in which case you just keep repeating the treatment regularly.

spider mites on leaves

You can also spray the plant with insecticidal soap when the infestation is still at an early stage. On the downside, insecticidal soaps will not work on an insect if it doesn’t come in direct contact with it.

plant pests on leaves

Chemical Alternatives

After all else failed, you may have to resort to using chemical solutions, but read the label to make sure it will not be harmful to your plant. It is also important to understand that a specific pesticide will not kill all kinds of pests—it is usually effective against specific pests but also at a certain life stage of the infestation.

In most cases, either using ecofriendly methods or resorting to chemical pesticides, one application of any treatment won't be enough, as some insects may be hidden or at the egg stage leaving the treatment dry out before affecting the insects.

Alternating Approaches

Switching between the type of treatment and pesticides is very important as some pests will develop a resistance to a pesticide, in which case you’ll have to use different pesticides as more than one application will be required.

4. Nutrient Deficiencies

Easier to cure than pests, a careful examination of the leaves or their quality will tell when it comes from a lack of nutrients. If the leaves are yellowing with particular patterns where the veins remain dark as it turns yellow in-between, brown spots, yellow edges, or yellow veins start to appear on the leaves, the plant is most likely lacking some essential nutrients.

Iron Deficiency

This will normally be seen in the new growth, causing stunted growth and yellowing of the tissue between the veins which retain their green color, from the decline of chlorophyll activity. Test the soil or get it tested, then adjust and keep the pH level below 7.

Potassium Deficiency

This can be diagnosed from older leaves showing brown spots or turning yellow on the edges or the veins turning yellow or brown. The condition can be altered by adding a potassium fertilizer with potash.

Nitrogen Deficiency

This causes stunted growth of the plant with the tips of the leaves turning yellow on the edges, or even the whole leaf sometimes turning to a pale yellow color. If you have used coffee grounds, adding it to the soil will increase the nitrogen level. You can also do it by applying a balanced fertilizer.

Magnesium Deficiency

This is usually detectable as they appear on lower leaves first as they start yellowing between the veins with the veins remaining green. This is can be corrected by treating the plant’s soil with Epsom salt (magnesium sulfate). It should only be used in gardens if the soil tests low magnesium levels.

Calcium Deficiency

This will cause the leaves to be crinkled, mottled, or distorted with their tips unable to grow. Adding agricultural lime to the soil will improve its calcium levels.

Old Age

Age is an ongoing process affecting everything in life that does not spare plants and flowers. A plant often just outlives its natural plant life, surrendering with leaves yellowing and aging out.

You must realize however that whatever causes your plant’s illness, it may take weeks or months for your plant to recover, so patience and perseverance are of the essence.