Hi, I have 4 japanese maples, 3 in pots and one planted in the ground. They did fine last summer, but this year the leaves started to turn brown on all of them. They don't seem to be dead, some of them even have new growth. They look like they were under watered but they haven't been. Anybody have a similar problem or insight?
Brown leaves can be several things. If the plants bark and buds look healthy, then it's a good sign that fresh new leaves will emerge next Spring. Water is one of the reasons. Over watering and under watering can cause brown leaves: The under watering makes perfect sense...brown=dry. Of course, the brown never shows up quickly. Many times it's because it was too dry at one point a week ago and now a week later it is showing signs. The onset of brown leaves usually takes a few days or a week to start showing up, which can be confusing. Always look back and analyze your watering schedule and weather conditions when signs of brown start showing up. Try to keep the root area somewhat cool and moist. A regular watering schedule, a little mulch, and keep your pots away from hot pavement can all help prevent brown leaves. Once it happens, nothing can be done to reverse it, prevention is key. Over watering = brown leaves makes no sense. That is, until we think about the fact that the tree's roots need oxygen to take up water. No oxygen = no water to the leaves to keep up with transpiration (loss of water in leaves, due to weather) = brown leaves. This is very confusing at face value and our instincts tell us to provide more water, making the condition even worse. This lack of oxygen in the root zone can lead to disease too. This abundance of moisture is taking place of the oxygen in the root zone. A few things to consider. Make sure your pots are free draining and offer plenty of surface area (avoid pots with trays at the bottom, small drain holes or too few drain holes, and avoid pots with a small surface area-tall and narrow or wide on the sides and narrow at the top and bottom). Check your soil mix. I find soil mixes too high in composted peat or sedge peat retain too much water and reduce the amount of oxygen to the roots. I am not saying these types of peat are bad, I use them, just not too much in my mix. Too little can result in the mix drying out too much and too much peat results in over saturation...It's all about balance. Also, if it is too much water, move the pots into bright shade as the leaves can no longer stand up to full sun. Once the water / oxygen is back in balance, they can slowly be moved out into more sun. Frost can cause brown leaves. Different areas get frost at different times or seasons. I live in an area where the last frost of Spring is the official start to the growing season and the first frost of Fall is the official end of the growing season. My area is safe right now, but other areas close by got hit with frost last week. Tis the season. Keep an eye on the forecast. If you are in an area of late frost then protect your maples. Environmental stress can cause brown leaves too. An example of this was the month of August in my area. In the beginning of the month (first two weeks) we had a push of very cool weather. With day temperatures in the upper 60's and lows in the 40's...very weird weather for us. My maples started to think it was fall and hints of colors started to appear. It was slow to get back to near normal seasonal temperatures. Then at the end of the month we had the week from hell. Heat, humidity, and a day time record breaking high of 105. This extreme swing caused brown leaves a few days to a week later. My maples had made it through triple digit high temperatures before, but it was when the trees were conditioned for such weather and not after they were showing early fall colors. Disease can cause brown leaves. We would need pictures to better understand what's going on in the event of disease. Pests can cause brown leaves. One pest in particular in my area that cause brown leaves are leaf hoppers. I do not hate much in this world, but I do hate leaf hoppers with a passion because they come on fast and are devastating to some of my maples. Lastly, maples that are getting pot bound tend to show signs of stress easier. If the trees were nearing time to repot when you bought them, then this may be the year that the trees are showing physical signs of being root bound. Slide the tree up out of the pot partially to see if they are becoming root bound.
Whole plant brown could be physiological, unless killed entirely by pathogenic infestation - otherwise in the latter case what is typical is a proportion of blighted leaves and branches, at least in the initial stages.
