Why is lemon tree dropping leaves?

Some causes of citrus leaf drop

Sometimes leaves are falling off a citrus plant, even though there is no sign of disease or damage. They just turn yellow and drop. In some cases they don’t even change their color and stay green until they fall.

Why is an orange, grapefruit or lemon tree dropping leaves? When is it an alarming sign?

Why is a citrus plant dropping leaves?

Citrus can lose its leaves of a few reasons: stress, overwatering and root damage or nutritional deficiency. Leaves can be also dropped of old age. I’ll tell about these situations later in this post. I’ll also elaborate on when the situation is alarming and how to fix it.

Leaf exchange

Most citrus species are evergreen 1With the exception of trifoliate orange and some of its hybrids., but their leaves live only two or three years, then they become yellow and drop. So, if a citrus plant has dropped only a few older leaves, there’s no reason to worry yet.

Yellowing and dropping of a few leaves doesn’t have to indicate a serious problem.

Solution: If a citrus tree has lost only a few leaves, you don’t have to take any action yet. Just monitor the plant and make sure it receives proper care.

But what to do if a citrus tree is dropping multiple leaves and its condition is getting worse? In such case the reason must be something else that just the leaf exchange. Let’s find it.

Plant stress

One of the most visible symptom of stress in citrus plants is yellowing and dropping of leaves. In case of a serious shock the leaves can also drop without changing their color, and the tree may become leafless.

Plant stress can be caused by:

  • sudden change of conditions
  • lack of light
  • drought or overwatering
  • root damage
  • cold soil combined with higher air temperature

Solution: Citrus plants prefer stable contitions, they should have time to get used to changes. During the season they need good amounts of light, water and heat, but when the winter comes, the rule is simple: the more heat the plant obtains, the more light and water it needs. If the temperature is high, but the light level is low, your citrus plant will become stressed and leaf loss will occur. So you basically have two options:

  1. Overwinter the plant in a cool place (with temperatures in range between 0 and 15 deg. C). In such conditions the plant needs much less light and water.
  2. Keep the plant in a warm and sunny place. If there’s not enough sunlight, use plant lights. Water when the top portion of soil becomes dry. You can limit watering to some extent to induce dormancy.

Overwatering

Overwatered soil is low in oxygen. When the roots can’t breathe properly, they die and rot. The plant becomes weak and starts to drop leaves; stems may dieback. That is a serious situation.

Citrus roots should have light color. The dark ones are already dead.

Citrus plants are being overwatered mostly in autumn and winter, when they need less water than during vegetation season. Their owner may be unaware of that and keeps watering the trees regularly, in the same manner as before. As a consequence, the roots rot and that exemplary orange, mandarin or lemon tree is dropping leaves.

Solution: Water citrus plants when the top portion of the soil becomes dry. Use well-aerated soil and ensure that the pots you’re using have drain holes. All the water should drain freely – the pot should never be immersed in water for more than 20 minutes.
If the roots have already rotten, place your plant in a warm and bright place and water it sparingly.

Nutrient deficiencies

Nutrient deficiencies may cause discoloration, and in severe cases dropping of leaves. Here, I’ll focus on nitrogen deficiency, which can produce similar symptoms to those described above: yellowing of leaf veins, then yellowing of the whole leaf and finally dropping the leaves, beginning from the older ones.

These leaves might have dropped due to overwatering and root rot, but also because of nitrogen deficiency.

What are the differences between symptoms of nitrogen deficiency and of plant stress or overwatering? First of all, when a plant is lacking nitrogen, its leaves become yellow, but can hang on the tree for quite a long time before they drop. The roots might be undamaged. Nitrogen deficiency occurs most often in well-drained soil with plenty of uncomposted organic matter (i.e. pine bark). After supplying nitrogen to the tree, the yellow leaves can become green again.

Solution: Proper fertilization reduces the risk of nutrient deficiencies. Soil pH for citrus plants should be between 5,5 and 6,5.
If your plant has been diagnosed with deficiencies, supply the lacking minerals with adequate fertilizer. However, before applying the fertilizer, make sure that the reason of leaf drop is deficiency and not plant stress or overwatering. Also try to avoid fertilizing in autumn and winter, except when the deficiency is severe.

How to find the reason of citrus leaf drop?

You already know that there are several possible causes of citrus leaf drop. How to find out why an orange, mandarin or a lemon tree is dropping leaves?

First of all, make sure that the dropped leaves are not harmed by frost, excess sunlight, soil salinity or overfertilization, fungus etc. If there are signs like dry leaf margins, discolorated spots etc., those leaves have probably fallen off due to damage. Only if the fallen leaves look unharmed, you should start to diagnose your tree with plant stress, overwatering or nitrogen deficiency.

If you’re sure that the leaves are not dropping due to some sort of damage, think about the history of your plant. Have you moved it recently to another location? Does it receive enough sunlight? Has it suffered from drought or overwatering? Those may be probable reasons of leaf drop.

Next, it’s good to check the soil and roots. If you can exclude plant stress and root rot, then think whether your plant receives proper fertilization.

After diagnosing the problem, it will be easier to cure the plant. Apart from the reason of leaf drop, the plant should receive enough sunlight and proper care – in such conditions it will regenerate better.