11 Reasons You See Yellow Leaves on Orchids

Yellowing leaves on a Phalaenopsis orchid, also known as a moth orchid, are not necessarily a cause for alarm. It's normal and natural for older leaves and stems to turn yellow and gradually drop off. But if all the leaves on your moth orchid are yellow, it could indicate that something is wrong. Several factors can cause yellow leaves on orchids, including direct sunlight, low temperatures, and root rot.

Natural Aging Process

Older Phalaenopsis orchids often have somewhat elongated stems where old leaves have dropped away. New roots will continuously emerge from the stem of healthy plants, eventually forming a mass of roots.

How to Fix

If you discover a yellowing leaf on the bottom of the orchid, don’t worry. This yellowing is a natural process of the plant to discard the mature leaf to produce a new leaf. However, if the leaves are yellowing from the top of the plant, there is a problem.

Too Much Light

The leaves of a Phalaenopsis orchid can burn and turn yellow if they are exposed to too much direct sunlight.

How to Fix

Try putting your orchid in a place that receives sufficient indirect sunlight. If you place the plant on a windowsill, make it a north- or west-facing window. If the leaves are still plump and firm but yellowing, the plant is most likely receiving too much light, and it's washing out the color.

Wrong Temperature

Next, ask yourself if the temperature is right. Ensure the temperatures around your orchid are between 65 and 80 degrees Fahrenheit during the day and 60 and 70 degrees Fahrenheit at night. Too-low temperatures can also cause orchid leaves to turn yellow.

How to Fix

Keep the orchid away from open windows, fans, or air conditioning vents. If you put your orchids outdoors in warmer weather, bring them inside well before temperatures plunge.

Watering Problems

The plant is most likely dehydrated if the leaves are wrinkled and listless. If not, check the roots. Overwatering can lead to root rot, which can, in turn, cause its leaves to turn yellow. 

How to Fix

Only water orchids when the top one inch of the potting medium is dry and the roots are white. Make sure there are enough holes in the pot to allow proper drainage. If your orchid is suffering from root rot, but you see your plant still has some healthy green roots, trim the rotted roots and repot the plant in a new orchid potting mix.

Humidity Issues

Orchids are tropical plants that require humidity to thrive. Most homes aren't moist enough for orchids. The preferred humidity range is 40 to 70 percent.

How To Fix

You can use a humidifier around your orchid or increase humidity around it by placing it on a humidity tray. Make a tray by filling a shallow dish with stones or pebbles, filling it with water, and setting the plant on top to soak up the moisture from the evaporating water in the tray.

Potting Stress

The best soil for orchids is a loose, fast-draining potting media that allows the roots to breathe. It should be changed when the potting media becomes too crumbly or physically starts breaking apart after a few years.

How to Fix

If the soil remains compacted or hard, change the soil to a high-quality orchid mix or sphagnum moss with perlite. The soil should also be changed if it becomes overly crumbly or smells acidic or foul.

Nutritional Deficiencies

Moth orchids need fertilizer during the summer, with a diluted orchid fertilizer usually every third to fourth week. If orchids do not get enough nitrogen and magnesium, they have trouble producing chlorophyll, turning the leaves yellow. If your orchids’ leaves begin to yellow around the tips and the sides, your plant is likely low in nitrogen, magnesium, or both.

How to Fix

Feed regularly but lightly.

Fungal or Bacterial Diseases

Yellowing leaves could be caused by a fungal infection that starts as yellowing areas on the bottom of the leaves. If the leaves are yellow and you notice a foul smell, it could be a bacterial or fungal infection. In most cases, it's caused by too much watering and may eventually lead to crown, root, or stem rot. Ultimately, it will turn black and affect both sides of the orchid leaves.

How to Fix

If you suspect it's a fungal or bacterial problem, separate the orchid from other plants to prevent the disease from spreading. Use a sterile pair of scissors to remove the affected area. Spray the plant with a fungicide to help it fight off fungal issues.

Pest Problems

Spider mites, scale insects, thrips, and mealybugs are common invaders of moth orchids. They reproduce and spread fast. They are often hard to see unless you inspect them carefully with a magnifying glass or look carefully under leaves. Some common telltale signs of a potential pest invasion include webbing or discoloration spots where bugs feed off the foliage.

Mites are tiny greenish-yellow bugs about the size of a sharp pencil point. They are fast movers, barely visible to the naked eye. Thrips have thin bodies and wings and can get bigger than mites, about 1/8-inch long. Mealybugs can almost get about 1/4-inch long with a white, fuzzy appearance. Scale insects are roughly the same size as mealybugs but are darker, rounder, and have a glossy-looking sheen to their armor-like outer shell.

How to Fix

You can wash many of these little bugs away with a strong blast of water. Also, physically wipe the leaves with a water-moistened washcloth or paper towel. For a significant infestation, spray the plants with a horticultural oil like neem oil or insecticidal soap. The best time to spray them is in the morning. After 15 to 30 minutes, hose off the oil or soap before the sun's intense rays reach the plant. Keep infected plants away from your healthy plants until the infestation has been remedied.

Environment Change

Transplant shock is a significant environmental change. Upgrading the size of a container, changing the soil, or root pruning can cause orchid stress. Removing roots can reduce a plant's water uptake ability, and the plant might want to lose leaves to compensate for the change.

How to Fix

Allow the plant time to acclimate to its new soil. Fresh potting media may have more nutrients, but it may also have a slight change in pH, which can affect a plant's ability to absorb nutrients.

Shipping Stress

When plants are confined in packaging for shipping, they are exposed to higher quantities of the naturally occurring hormone ethylene that all plants produce when decomposing. So, if a plant is shipped with one dying leaf, the other leaves will be exposed to higher concentrations of that hormone, triggering them (older leaves starting first) to begin the decomposition process.

How to Fix

Once the plant is unpacked and given fresh, circulating air, its youngest leaves should recover; however, you might lose one or two of the oldest leaves. To prevent this, ask the plant shipper to include ethylene-absorbing packets when shipping. This is a standard shipping practice with plants.

How to Prevent Orchid Leaves From Turning Yellow

To prevent orchids from losing their leaves and premature yellowing, replicate their natural, native environment as best as possible. Provide the proper water level, humidity, temperature, lighting, air circulation, soil composition and drainage, and nutrients, and keep the bugs and diseases at bay. Plants that have all their ideal parameters met and maintained will thrive.