Last updated on March 29th, 2022
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Citrus trees like lemons are susceptible to a wide number of diseases, pests and nutritional deficiencies. They can be impacted by simple environmental stresses as well. So, if your lemon tree is losing its leaves, there are many possible explanations.
Environmental Reasons that often cause leaf drop
Environmental reasons are the first likely cause. Severe cold, improper watering, not enough watering, too much watering, all lead to environmental conditions that subsequently manifest in the leaves dropping off your plant.
Cold damage can be very detrimental. Lemon trees do not like cold or freezing temperatures. If the temperature has dropped to -2°C for more than 4 hours it can cause all the leaves to drop off your lemon tree because of what is known as Winter Leaf Drop. If the temperatures are at 0°C you need to protect any trees that are under 5 years old by covering them with horticultural fleece or moving them somewhere more protected.
The best way to grow lemon trees is in containers and ideally, the minimum temperatures at night need to hover around 10°C. With this in mind, it is why we always strongly recommend bringing lemon trees indoors during the winter and placing them outside during summer.
Pruning too late in the season
If you do live somewhere milder, for example, further south, then you may have them in the ground. With this in mind, equally important is watering 48 hours prior to any freezing temperatures and then postponing pruning until spring. If you prune too early or you water right before freezing temperatures, this leaves the plant more susceptible to Winter Leaf Drop too.
Overwatering is a common cause of leaf drop
Overwatering is a common cause of leaves dropping off a lemon tree, especially if you have moved your lemon tree inside to avoid the colder weather. Overwatering during winter is one of the most common causes of leaves dropping off.
If you allow the roots to sit in water they can develop root rot and eventually the leaves will fall off. To help with this you can mulch around the roots, minimise your irrigation, and make sure that you plant your lemon tree in well-draining soil so that it doesn’t have this problem. With plants grown in containers, it’s best to let the surface of the soil dry before watering.
Lack of nutrients causes leaves to turn yellow before dropping off
Nutritional deficiencies can be very problematic. There are 16 essential nutrients that lemon trees need to grow and if they don’t get enough of any one of these 16 it can cause their leaves to fall off. A nitrogen depletion is the most common cause followed by insufficient levels of magnesium, iron, and zinc.
All of these things can cause the leaves to fall and negatively impact the production of fruit in both quantity and size. To help keep your lemon tree healthy, give it a fertiliser once a month when it’s in the growing seasons (summer and spring) with a citrus feed. Fertilise only once every quarter in autumn and winter.
Diseases if left uncontrolled can lead to lemon trees loosing their leaves
There are, as mentioned, a wide array of diseases that can also affect your lemon tree and cause the leaves to fall off. Things like Alternaria leaf spot cause brown spots, blackening along the veins, sunken fruit, and subsequently leaves dropping off. Similarly, greasy spot fungus is a fungal disease that can cause yellow spots on your leaves and eventually produce brown blisters until such time as the leaves fall off.
Copper fungicide should be sprayed in the spring and then again 4 weeks later and applied between every two and four weeks from April through June. This will go a long way toward helping your plant fight off any of these diseases.
Bad infestations of pests can cause leaves to drop if they aren’t controlled quickly
Pests can result in leaves falling off your lemon tree. Things like spider mites will eat the sap out of the leaves and leave a honeydew behind which causes black sooty mould to develop. It’s important to eradicate an infestation of any pests immediately. There are some pests like the citrus leafminer that literally mine out the soft tissue inside the leaves eventually killing the tree.
With pests, the same as with diseases, preventative measures are best. Providing the right feeding schedule, the right amount of water, good soil, proper airflow, and keeping your eyes peeled for the early symptoms will go a long way toward helping you identify and immediately rectify any issues your lemon tree is having.