Help, my lemon tree is losing leaves – that helps!

A lemon tree usually loses a significant (and critical) amount of leaves when the balance between the roots and the foliage is disturbed. The causes for this can be very different, often it is not a single reason, but an interplay of different factors that ultimately lead to the fact that the water and nutrient cycle between leaves and roots no longer functions smoothly. In contrast to the natural conditions under which outdoor plants grow, potted plants often have unnatural site conditions that cause such an imbalance. It may be that the roots are in winter while the leaves are in summer (or vice versa).

The most common causes are:

• light mangle
• sunburn
• roots that are too cold
• Lack of water
• Waterlogging
• Pest infestation

Recognize the cause – fix the problem

The most common causes of the lemon tree losing all of its leaves vary depending on the season. Before doing anything, you should take a closer look at the plant, the site conditions and the fallen and preserved leaves. Then it is at least possible to clearly limit the reason for the leaf shedding.

1. Problems in spring

Since citrus plants are not hardy, they must be overwintered frost-free. In spring it is important to find the right time to put the lemon tree outside again.

Hypothermic roots
Hypothermic roots occur when the temperature of the root ball is below 12 degrees and at the same time the foliage is warmer than 18 degrees. In this case, the roots are unable to cool the leaves adequately with water. As a result, the leaves fall off. The problem occurs especially in late winter or early spring, when the temperatures are still cool but the sun is already gaining strength. The ratio of light to temperature is too high. So it is not a question of a lack of light, but rather an oversupply.

Sunburn
If there are silvery or brown spots on the leaves or if the leaf tips turn brown, it is often sunburn. Often the phenomenon only occurs on the side facing the sun. The causes are the same as with hypothermic roots: the plant is unable to pump sufficient water into the leaves to cool them. So if the roots are relatively cool and the sunlight is high, there are problems with cooling the leaves. In the worst case, the lemon tree sheds all of its leaves.

Immediate measures
In both cases you must immediately move the plant to a slightly more shady, sheltered place. Covered areas such as a location under a balcony are suitable. It is also beneficial to be close to a wall that stores solar heat during the day and releases it again overnight. On the east side of the house, the plant is also protected from the blazing midday sun. If more frosty nights are to be expected, bring the lemon tree back to the garage or house overnight as a precaution.

Prevention
Only place the lemon tree outdoors if the temperature forecast is above 5 degrees in the long term. First, a partially shaded, sheltered spot in the garden is advisable – and bring the plant back into the house as soon as icy nights appear. Do not expose the lemon tree to direct sun in the first few weeks, but slowly get used to the changed light conditions.

2. Leaf loss in summer

If the lemon tree is in a sunny, warm place in the garden or on the balcony, extreme leaf losses are seldom to be complained about. At this time of year, the temperatures and light conditions are ideal – good conditions for healthy plant growth. However, if the lemon tree loses all of its leaves, the main reasons are:

Lack of water
A lemon tree evaporates a lot of water through the leaves at high temperatures. This transpiration creates evaporative cooling, which the plant uses to prevent overheating and thus damage. As the temperature rises, the tree has to evaporate more water in order to maintain the temperature. If it can no longer supply enough water via the roots, this cooling is interrupted and the plant burns or dries up.

Tip: Even in the early stages of a lack of water, the lemon tree begins to shed flowers, fruits and individual leaves in order to limit the rate of evaporation.

First signs : leaves curled up, slightly sloping downwards

Immediate measures
Make sure you get the plant out of the blazing sun and place it in a little shade. It is usually sufficient to place the lemon tree protected from the midday sun, for example under a tree or next to a wall that provides shade at this time of day. If the lemon tree has already lost a large part of its leaves, it should not be immersed because the water can no longer evaporate through the leaves. In this case, lukewarm water is used only moderately. If the watering behavior is okay, it can also be that the lemon tree can no longer absorb the moisture well because the soil is very compact. In this case, repotting in a more permeable substrate can help.

Prevention
Regularly check the root ball for moisture. If the top layer is already dry, it must be poured again. Never let the soil dry out completely, but be sure to avoid waterlogging, because the plant cannot tolerate this either. If you cannot check very often whether the plant still has enough water, place it in a little shade as a precaution (but still very light). Pour only with warmed water. Ice cold water from the garden hose leads to hypothermic roots!

3. Leaf fall in early winter

Many hobby gardeners experience their first shock in October or November when the pretty lemon tree suddenly loses all of its leaves after moving to its winter quarters. In the absence of more precise information, many people make a fatal mistake out of ignorance: They put the potted plant directly from the already cool outdoor location into the warm, dark apartment. The result: the plant sheds all leaves.

Lack of light
Ist is warm, the lemon tree needs a lot of light for photosynthesis. Compared to the lighting conditions outside, it is, so to speak, pitch dark in the apartment. The loss of leaves is therefore a protective mechanism of the plant.

Immediate measures
To break this cycle, two different measures help: Either the plant has to be lighter or cooler. The optimal choice is always a cooler location, as this prevents further problems: dry air. An ideal winter quarters for the lemon is light and cool. The temperatures should preferably be between 5 and 10 degrees. If it is not possible to keep the lemon tree cool, there is a second alternative: provide more light!

Prevention
You should preferably find a very bright and cool wintering place for your lemon tree. Locations where temperatures between 5 and 10 degrees are constant are ideal. This can be an unheated winter garden, a very bright garage or even a greenhouse. Good lighting conditions are essential in warm locations. If the light intensity of the winter sun is not sufficient, you should get a special plant lamp.

Pests

Warm temperatures, lack of light and dry heating air in the winter quarters severely weaken the lemon tree, making it susceptible to various pests. Most common are sucking insects such as spider mites or lice. They can be recognized on the one hand by stunted and drying shoots, as well as on white webs. The fallen leaves are also covered with a sticky layer.

Immediate measures
Cut out dead and heavily infested shoots generously and shower the plant with the shower head (especially the underside of the leaves). In some cases, home remedies help, such as spraying a solution of water, soap, and alcohol every day. If the infestation is very advanced, sometimes only a pesticide can save the tree from dying. However, since lemon trees are very sensitive to some of the remedies, you should seek detailed advice from a professional before using them.

Tip: Place the lemon tree in a slightly cooler location.

Other factors

In addition to problems with temperatures and light conditions, there are other factors that may lead to leaf shedding:

Nutritional deficiency

Whitish or light yellow spots on the leaves indicate that the plant is suffering from a disruption in mineral utilization caused by an excess or an undersupply. Chlorosis is one of the most important deficiency symptoms. If the substrate is very calcareous, the lemon tree will not have any iron available. The iron can still be present in sufficient quantities in the soil, but due to the high pH value it is no longer available to the plant. If there is a lack of iron, the leaves cannot develop enough leaf green and photosynthesis is significantly reduced.
Symptoms: whitish or light yellow leaves with dark green veins

Immediate measures
In the short term, foliar spraying with fertilizers containing iron chelates from specialist dealers is possible. Lemon trees tolerate several diluted sprayings better than a high dose administration. But this does not solve the general problem. In addition, the pH value in the soil must also be lowered. This can be done with special fertilizers.

Tip: Alternatively, repotting in commercially available citrus potting soil ensures a better supply of nutrients in the long term.

Loss of leaves under stress

A less specific cause for the shedding of the leaves on lemon trees can be stress. If the site conditions change suddenly, in some cases the plant cannot adapt quickly enough and loses considerable amounts of foliage. The same thing can happen if you water the plant with ice cold water. Plant stress is not always a predictable factor for the gardener and must be classified as an unfortunate mistake in care that should not be repeated anytime soon. The lemon usually recovers on its own after a short time.

Waterlogging

Waterlogging can occur at any time of the year. If the water is permanently in the root area, they start to rot and bacteria and fungi spread.
Symptoms: Leaves turn yellow and fall off without drying out beforehand

Immediate measures
Now is the time to act quickly to save the lemon tree from dying. Get the root ball out of the pot and remove as much of the wet soil as possible. Also, cut out all soft and diseased roots down to the healthy tissue. Pot the tree in fresh substrate that is specially adapted to the needs of the lemon.

General first aid measures in case of leaf loss

It is not always obvious at first glance what exactly went wrong and why the lemon tree is losing its leaves. If the leaves are trickling and no pests can be identified during the inspection, the following immediate measures will help:

• put the plant into hibernation
• Temperature: 5-10 degrees
• place a little cooler in summer
• if leaves are lost in late winter: shading necessary
• Leaf loss in summer: shade and water regularly
• Repot in a good citrus substrate

Worst mistake when losing leaves

The biggest mistake you can make when your lemon tree is losing all of its leaves is to over water it! Since the plant no longer has any leaves, it cannot evaporate the water through the leaves. The result is waterlogging. Then not only are the leaves of the lemon tree gone, but also its roots have died. As a rule, the tree can then no longer be saved and it dies irrevocably.

Conclusion

If the lemon tree loses all of its leaves, this is almost always due to an imbalance between water absorption by the roots and evaporation via the leaves. If this equilibrium is restored, you will also stop leaf shedding and the plant will recover. In most cases it helps to put the plant a little cooler (but light) and thus simulate the resting phase.