Hello, I am new to having a Meyer lemon tree. I got this one about a month ago. It was doing great but some problems arose approx. two weeks ago. First some leaves were yellowing from the stem, I read this was a sign of low nutrients so I fertilized with a 10-5-5 slow release and this yellowing seems to stop. (Not sure if this is relevant just wanted to mention it). Now the leaves seem a bit drooped, have patches of lost pigment and there are dry brown spots on some (I’ve attached some photos). Additionally many leaves have fallen off (most without the stem indicating stress). Additionally when I first got the plant there were maybe 30 flowers about 15-20 got fertilized but now there is only one new flower. I think I had mites (saw a few tiny webs and one bug) so I sprayed the plant in soapy water ~4 times and wiped down each leaf and haven’t seen anything since. The plant gets a good amount of sun, prior to it being warm and putting it on my balcony I had it under a grow light for 9 hours a day. I still bring the plant inside at night as it has been dropping to less than 10C. Would appreciate any advice!
Those dry patches could be a fungal infection or damage from the soap spray. Either way I would pick off the damaged leaves as they can either spread an existing infection or acquire one due to the damage becoming infected. In future if you see spider mites you may want to consider a different spray, or instead give the plant a good spray in the shower with warm (not hot!) water as that can also help control mites. Some soap sprays can damage leaves, especially if the leaves are then exposed to strong sunlight. Citrus are heavy feeders so giving it fertilizer is a good thing to do.
The leaf damage may be due to mesophyll collapse: Citrus: Identifying Diseases and Disorders of Leaves and Twigs—UC IPM. Droopy leaves (even though soil is moist) could be a sign of root damage, perhaps due to rot from a saturated medium. Allow the soil to become somewhat dry before watering. I also recommend the use of a commercial insecticidal soap. The articles in this post may be of interest: Monstera Deliciosa help!. Though not related to the immediate problem, I suggest the use of a high-nitrogen, water-soluble fertilizer containing micronutrients.
I suspect poor soil aeration. Citruses like well drained, well aerated soil. Peat and compost are not optimal substrates for citruses. I see no sign of fungal disease or nutrient deficiency. Another thing, citruses don't like rapid changes in environment conditions. Shuffling out and in can cause some stress. Night time temperatures slightly below +10ºC are ok for citruses. I shuffle my mandarins in only if frost is expected, they look nice despite our night time temperatures are often ca +5ºC. Never fertilize your trees if they are stressed because of some other cause than nutrient deficiency. Signs of nutrient deficiency never appear suddenly, if the condition of the plant worsens rapidly, then that is never caused by nutrient deficiency and fertilizing can do more harm than heal..
Appreciate the advice. Referring to the fertilizer I noticed some leaves yellowing at the stem and added fertilizer about 3 weeks ago, this seemed to stop it. I did recently repot the tree (I didn't realize how high up the root system stayed) and used the Pro-mix cactus mix. Do you recommend moving it back to a smaller container? Or a different soil mix I should try (I am open to making my own mixes)? After the two previous posts I cut off the damaged leaves to prevent them from getting infected and also gave the plant a good water (I think I may have been too paranoid about overwatering). I was planning on leaving the tree for about a week to see if this helps.
Consider repotting if the tree had been planted in an over-sized container. There should be a 3/4" inch or so of space between the root ball and the container's side. I'm not familiar with Pro-mix but whatever medium you use should be porous. Typical peat-based mixes are too dense and need to be amended with additional materials such as bark chips, calcined clay, and perlite.
That is similar to the spacing currently for the sides, however there is a good amount of space below the root ball I would say maybe 4 inches. The promos soil I added was this one PRO-MIX Cactus Mix.
Then it's probably better to leave it as is. The taller container will help in releasing moisture from the medium. Can't really tell from Pro-mix's product description on whether it is appropriate to use. The medium must be loose enough to allow air to enter. A cactus mix is not necessarily a good one to use. I had one which sat in its bag for a number of years. The contents had dried and compacted over time and had become rock hard. An amended mix with coarser materials will allow air to remain in the medium even after irrigation.