Yellowing kumquat leaves are due to the tree experiencing stress because of an environmental factor. The first step in fixing the problem is to correctly identify what is causing the leaf discoloration in the first place.
The most common causes of yellowing kumquat leaves are improper watering, low temperatures, disease, pests and natural leaf drop.
In this article, we will discuss the common causes of kumquat tree leaf yellowing and what you can do to remedy each one.
What is a kumquat?
The kumquat is a fruit tree native to the tropics. It has become increasingly popular in the US because aesthetically it makes a great landscape plant. Because of its size, it can be planted in a garden or in large containers.
The kumquat has olive-sized fruit and glossy green leaves. It belongs to the same genus as other citrus fruits like lemons and oranges, and can be grown quite easily in garden pots. Its fruit tastes sweet when ripe and has edible skin. It can flower and produce fruit twice a year. In ideal living conditions, the tree can grow two feet every year.
How do you care for a kumquat tree?
One of the most important things to remember when growing a kumquat tree is proper watering. Keep the soil moist but not soggy or constantly wet. You will know if you need to water the plant by pressing your finger into the soil. If the top two inches of soil still feel damp, do not water and check the soil again in one or two days. If the soil is dry, you can water the plant. Do this by soaking the soil in the pot until you can see the excess water flow out of the drainage holes at the bottom. You can put pot feet under the pot so that the plant does not sit in any stagnant water.
If the tree is planted in your garden, you can keep the soil around it moist by applying a layer of mulch on the ground. This is necessary during the first few years of the kumquat’s life because it thrives in moist soil. Just make sure to keep the mulch a few inches away from the tree’s trunk to avoid fungal problems. Once the tree has adapted to the mulch keeping the soil moist, you do not really need to water it any more, except during dry spells.
Temperature and humidity
Kumquats are tropical plants, so they do not do well in cold weather. If you live in an area with cold winters, you should take the plant indoors. You can take it back outside after the last frost of spring. Put the plant in a sunny spot where it can still be protected from chilly nighttime temperatures. Gradually harden the plant by leaving it outside for progressively longer periods until you can leave it outside permanently for the summer.
Kumquat trees prefer 50 to 60 percent air humidity. This can be difficult to achieve in the winter when the plant is indoors and the central heating is on. Mist the leaves with water to make the air more humid around the plant.
Kumquat trees like to be under full sun and they prefer to get at least six hours of sunlight a day. In the winter when the plant is indoors, give it as much light as possible by placing it near a sunny window. If there is little sunlight, you can use a grow light with one cool and one warm bulb. The grow light should be enough to provide the plant’s light requirement until you can take it back outside in the spring.
Kumquats like acidic soil, but they can survive in soil of any pH. If you plant the kumquat in a garden, make sure you enrich it by adding high-quality potting soil. Try not to plant it in dense soil like clay, because the water will not drain well and the roots may rot. You can use cactus or succulent potting mix for the kumquat to ensure proper drainage.
Why are the leaves on my kumquat tree turning yellow?
Giving the kumquat too much or not enough water can cause yellowing and dropping of its leaves.
Overwatering can happen when the kumquat is planted in poorly draining soil in a pot that does not have drainage holes at the bottom. The water is retained for too long, meaning the roots of the plant are soaked in the waterlogged soil where they cannot dry out or get access to oxygen. Eventually, the roots will die and rot. Root rot is caused by bacteria or fungi that make their way into the plant’s system through the vulnerable roots. The rot will climb up the roots and into the stem, branches and leaves. The leaves will turn yellow and fall off due to the excess weight of all the water.
Underwatering can also damage your kumquat plant because it will no longer be able to take in either moisture or the nutrients it needs from the soil. Plants need water to transport essential nutrients from the soil. If there is no water, the plant will shrivel and turn yellow or brown. You can remedy an underwatered kumquat plant by soaking the soil in the pot with water until you can see the excess flow out of the drainage holes at the bottom of the pot. This ensures that all of the soil has been soaked and all the roots have access to water. Eventually, the plant will bounce back and regain its original vigor. Just make sure you no longer forget to check whether the plant needs to be watered.
Kumquat trees lose both their leaves and their fruit after a frost, even though the tree itself has been known to withstand temperatures as low as -20 degrees Fahrenheit. Do not prune your kumquat tree until after the branches have died back, even if the tree is an eyesore in your landscape.
Prevent cold damage by bringing a potted kumquat indoors or to an area where it can get adequate shelter from the elements. If the kumquat is in your garden, remove the mulch around the tree, water the soil, cover the tree and use a heater if you deem it necessary.
Disease and pests
As mentioned above, kumquats are susceptible to root rot when their roots are overwatered. They are also susceptible to mealybugs.
Root rot can be due to a fungus or bacteria. Avoid this by making sure no excess moisture is retained in your plant’s soil. Plant the kumquat in well-draining soil and use a pot with drainage holes at the bottom. Try not to put mulch at the very base of the tree; only mulch several inches away from the base. Mulch helps retain moisture in the soil, so placing it on the base of the tree will contribute to waterlogging of the soil.
Aphids are another pest that can attack your kumquat tree. You can try to control them using natural predators, such as ladybugs, or you can use neem oil. Apply the oil to the tree early in the season, once a week for a month, to kill all the insects on your tree.
Natural leaf drop
The yellowing of the leaves on your kumquat tree may be due to something as normal as natural leaf drop. As long as the yellowing leaves are mostly at the bottom of the tree and they fall off gradually and not all at once, it is probably nothing to worry about. This is especially true if the rest of the tree looks healthy, and there is nothing you need to do in this situation.
Kumquat leaves turning yellow is a sign of an environmental factor that is causing the plant stress. The first step in fixing the problem is correctly identifying the cause of the discoloration.
The most common causes of kumquat leaf yellowing are improper watering, low temperatures, disease, pests and natural leaf drop.
Kumquats are hardy plants and it does not take much to grow them properly in your garden. As long as you provide them with their basic needs, you will have this beautiful plant and its fruit in your home for many years.
Image: istockphoto.com / JorgeMoyol