I've been growing two avocado plants for about 10 months now, and I'm noticing the leaves on one plant are turning dark brown around the edges and the other plant has drying around the edges with overall wilting leaves. I've attached pictures. I live in a very cold climate this time of year, in a basement apartment. I usually leave a daylight lamp on for the plants during daylight hours, and they are a few feet away from our heater on the wall. I've read browning can be caused by too much sodium, so I've been leaving their water out for a day before giving it to them, but I'm not sure how much that really does. I cut off all the brown bits, but it's coming back.