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Last updated on January 21st, 2020
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 often cause leaf drop
Environmental reasons are the first likely cause. Severe cold, improper watering, not enough watering, too much watering, these all lead to environmental conditions that subsequently manifest in leaves dropping off your plant.
Low temperatures cause leaf drop
Cold damage can be very detrimental. Lemon trees do not like cold temperatures or freezing temperatures. If the temperature has dropped to -2 degrees Celsius 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° Celsius you need to protect any trees that are under 5 years old by covering them with horticultural fleece or moving them somewhere more protected. Now the best way to grow lemon trees is in containers and ideally, the minimum temperatures at night need to hover around 10 degrees Celsius minimum. With this in mind, this is why we always strongly recommend bring lemon trees indoors over winter and placing them outside during summer.
Pruning too late in the season
If you do live somewhere more mild, for example, further south then you may have them in the ground. With this in mind, equally important is 2 water 48 hours prior to any freezing temperatures and then postpone pruning until springtime. If you prune too early or you water right before freezing temperatures, this leaves the plant more susceptible to Winter Leaf Drop too.
Over watering is a common cause of leaf drop
Over-watering is a common cause of leaves dropping off a lemon tree especially if you have moved your lemon tree inside for the colder weather. Over-watering 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, minimize 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 its 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 quantity and size. To help keep your lemon tree healthy, give it a fertilizer once a month when it’s in the growing seasons, summer and spring with a citrus feed. Fertilize only once every quarter in autumn and winter.
Diseases if left uncontrolled to leave to lemon trees to loose their leaves
There are as mentioned a wide array of diseases that can also affect your lemon tree and causes 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 springtime 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 leaf drop if not 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 investigation of any pest immediately. There are some pests like the Citrus leafminer that literally mine out the soft tissue inside the leaves that eventually killed 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.