Orchids are a popular flowering plant that comes in numerous shades, from the bold violet varieties to the more cheerful yellow and the demure pink members of the Orchidaceae family.
While orchids are known to be reasonably hardy, one common complaint found among gardeners is the yellowing of leaves. If yellowing is confined to older leaves, this is nothing to worry about: this is part of the natural process for older leaves to fall off to make way for new growth.
However, there are times when yellowing leaves are a sign of poor plant health.
This guide teaches you how to determine why your orchid’s leaves are turning yellow and what to do to remedy this.
Reasons Why Orchid Leaves Turn Yellow
Overwatering The Orchid
Overwatering is the most common cause of yellow leaves for orchids. Since orchids are epiphytes, they grow on trunks of other trees to keep their roots relatively dry. They also draw moisture from the air to supplement their water needs.
For these reasons, orchids are sensitive to overwatering.
Whether your orchids are planted in a pot or your garden, overwatering can flood the roots, cutting off their air supply, which prevents roots from being able to absorb nutrients. This suffocating of roots leads to root rot, and the slow loss of the green pigment chlorophyll causes the yellowing of the leaves.
How To Fix it?
The yellowing of leaves caused by overwatering can become apparent in a few hours or days. While it may look like your orchid is wilting, you can save it by taking these steps:
- If the plant is waterlogged, gently take the orchid out of its potting mix and leave the roots to dry overnight.
- Cut off any roots that are wholly blackened and dead using clean, high-quality garden shears.
- Lightly spray remaining roots with 3% hydrogen peroxide to kill any bacteria that may have grown in stagnant water.
- Repot the orchid in fresh, well-draining potting mix the next day. Make sure you are using a pot with drainage holes to ensure excess water can be drained and doesn’t pool at the roots.
An orchid should ideally be watered once every seven to fourteen days. Before watering, insert your finger about one to two inches into the soil or potting mix to see if it’s wet. If so, wait another day or two before watering the plant. If the soil is dry, water the plant until excess water escapes from the drainage hole.
Sometimes you may not be excessively watering the orchid, but the signs of overwatering may be present. In this case, you should review the potting mix used for the plant. The usual moss mix is unsuitable for orchids as it retains too much moisture. Use a well-draining potting mix instead.
For more tips on rescuing an overwatered plant, read our guide here.
Underwatering The Orchid
Just to make things confusing, underwatering can also lead to yellow leaves! If the roots do not receive adequate water, they cannot absorb nutrients, and the leaves start drying out and dying.
White-grey roots are the first sign that your orchid is not getting enough water. Observe if the leaves are limp, wrinkled, and dried-up, tell-tale signs of underwatering. In longstanding cases, the stem may also soften and wilt.
You can differentiate between overwatered and underwatered orchid leaves by checking the soil moisture. Additionally, the yellowing of leaves caused by underwatering makes the leaves appear brittle, crisp, and brown, whereas the yellow due to overwatering will make the leaves look mushy and limp.
Orchids may take some time to recover from underwatering, so do not be alarmed if your plant starts losing its leaves.
Sometimes you may be watering your orchid regularly, but it still displays signs of dehydration. This may occur when the soil is tightly packed and does not allow water to reach the roots. In this case, you might try repotting your orchid in a well-draining potting mix.
How To Fix It?
Yellowing leaves due to underwatering has a simple solution: water the plant. Even then, try not to be overzealous and inadvertenly overwater your orchid. Instead, start watering the plant regularly, once every 7-14 days, while checking that the soil is dry with your finger before watering (if not, hold off for another day or two).
This routine watering will be enough to revive the roots and resume the transport of water and nutrients to the rest of the plant. When watering, ensure that excess water escapes through the drainage hole: this ensures that you are not watering too shallowly, which deprives deep roots from moisture.
Also ensure that your tropical plant has high (>50%) levels of humidity, so that leaves are not losing most of the moisture to the air. Utilise a humidifier if needed.
Direct Sunlight Scorching The Leaves
Orchids thrive in indirect, filtered sunlight. Direct sunlight can scorch the leaves and cause discolouration of the plant. Sun damage can appear as yellow leaves with burnt edges and white patches, surrounded by a brown circumference. Such damage is a sign an excess of direct light.
Sometimes overexposure to sun may also cause purple discolouration. The discolouration may start as little yellow or brown spots. If the plant is not moved in time, the spots will enlarge into spots and overtake the leaves, causing them to wilt.
Since orchids mostly grow under a canopy of trees in nature, their native habitat does not allow direct sunlight to reach the plant. While some orchids may be labelled as high-light orchids, even they can not survive in the direct afternoon sun.
How To Fix It?
While direct sunlight may be harmful to the leaves, orchids still need light to grow properly. The solution to this dilemma is adding a shade cloth or screen. This will allow the area surrounding the orchid to be well-lit without the sun scorching the leaves.
If you want to place your orchids on a windowsill, the best choice would be east-facing windows, which receive early morning sunlight, which is not as strong. North and west-facing windows receive the perfect amount of sun from recreating the tropical setting and hence are a good option. South-facing windows receive too much afternoon sun, so those are a no-go.
If the leaves continue to yellow and new burnt edges appear, it might be time to move your orchid away from the window altogether.
Low temperatures can also be the reason behind the yellowing of your orchid’s leaves. These tropical flowing plants are very sensitive to low temperatures, and the leaves start taking on a pale hue if the temperature falls below 60 degrees F (15 degrees C). Keeping the thermostat between 60 to 85 degrees (15 to 30 degrees C) is ideal for orchids to grow.
Low temperatures can stress your plant, which will appear as yellowing of leaves, along with signs of leaf drop, browning of leaves, and plant death.
Cold drafts also cause yellowing of leaves. Orchids will complain about lower temperatures with droopy blooms. If not fixed, the leaves will wither and die. Even short-term exposure to a temperature below 60 degrees F (15 degrees C) can cause significant damage.
How To Fix It?
The first step to recover the droopy yellowed leaves of your orchid exposed to cold temperatures is to take them away from the frigid environment. The tropical plant is used to higher temperatures with humidity.
Providing a stable temperature environment can help rejuvenate the plant enough to grow new leaves if the yellowed ones are not salvageable. Ensure your room has a thermostat that you can keep an eye on, preventing the temperature from falling below 60. In addition to that, you can also move the orchid away from open windows or any other source of exposure to cold drafts.
Adding fertiliser regularly is a good habit that helps the plants thrive. However, orchids are sensitive to over-fertilising, especially when the plant is not actively growing.
Adding too much fertiliser can lead to a build-up of nutrients such as calcium, manganese, copper, or zinc. Excessive nutrients can prevent the roots from taking up iron when the plants do not need them, leading to chlorosis (a lack of chlorophyll). Chlorosis causes the yellowing of leaves.
How To Fix It?
Orchids are light-feeding plants. They do not consume a lot of nutrients, even during periods of active growth. Water-soluble fertilisers are the best option for orchids. We recommend this orchid fertiliser. Alternatively, use a houseplant fertiliser at half-strength, but ensure that it does not contain harsh chemicals like urea.
During summer where your plant is actively growing, adding fertiliser every two weeks is best. During winters, adding fertiliser once a month will be more than enough as the plant needs are less, and leaving excess chemicals in the soil will harm the plant.
Another point to note is that orchids are especially sensitive to fertilisers during budding and flowering stages. Therefore withhold fertiliser when your plant is in full bloom, and fertilise budding orchids every 4 weeks instead.
Plant Diseases & Nutrient Deficiency
Plant diseases can also cause the discolouration of leaves. Brown and fungal leaf spots cause yellowing of leaves and occur due to infection with either bacteria or fungi. Similarly, nutrient deficiencies also play a role in yellowing on orchid leaves.
Nutrient deficiency often occurs when the fertiliser isn’t changed sufficiently (if you are using compost-based fertiliser), especially during periods of active growth. Most of the time, plant owners think the potting medium must have all the nutrients required to keep the plant healthy. However, once these nutrients run out, the leaves start turning yellow, which is an orchid’s way of telling you something is amiss. Common elements that may become deficient in orchids are nitrogen, iron, calcium, and zinc.
Fungal leaf spots on the leaves are areas of brown discolouration which enlarge with time and take up the entire leaf. Bacterial brown spots commonly occur when the orchid is placed in a hot and humid area, leading to moist-looking mushy brown or yellow leaves.
How To Fix It?
Nutrient deficiencies are comparatively easy to fix. Simply use fertiliser every two weeks to the plant during summer and spring, so the orchids have sufficient nutrients to bloom. In winters and autumn, the need for nutrients dwindles, so adding fertiliser can be done once a month.
If you suspect bacterial brown spot, cut off any damaged parts of leaves or an entire leaf depending on the extent of the damage. Remember always to use sterile garden shears. After that, use a broad-spectrum bactericidal spray on the plant to prevent the growth of bacteria. Cut off the infected leaves for fungal leaf spots and wipe the healthy leaves with the fungicide spray.
Repotting plants is often considered healthy and is even advised. However, this course of action may have the opposite effect on orchids. Orchids like to be crammed and do not take well to repeated repotting.
As long as the roots appear green and healthy, there is no need to repot the plant. Fluctuating environmental conditions can lead to transport shock and cause yellowing of leaves.
How To Fix It?
Avoid repotting orchids unless you see signs of distress or when necessary. By providing a consistent environment after repotting, you can prevent the leaves from turning pale and dying. Carry out the repotting according to growing seasons and aim to transport the plant every two years to give it sufficient time to deplete the soil of any nutrients.
Deborah is a plant enthusiast and founder of Gardening Collective.