Big leaf maple care

Asked July 16, 2017, 5:35 PM EDT

I've got a tree that is about 17 years old and about 35 feet tall and wide. Part of the tree is sheltered/shaded while part is in full sun. The shaded side seems to develop what look like mildew spots early in the season that clear up. The sun side starts to crisp up around the edges of the leaves by mid summer. Recently the smallest under branches have been looking chlorotic and dropping leaves in what looks like some sort of self-pruning. We had a lot of rain this last season but I've been trying to keep watering the tree through the summer to prevent early leaf drop (some years it's happened as early as June.) No signs of rot or basic damage. Am I watering too much/little. Should I ammend the soil? Thoughts? (Oh, and yeah, I'm cheating and I'm in California in zone 9, with soil that is mostly imported fill of unknown origins.) Help a girl out?

Oregon big leaf maple

1 Response

Thanks for your maple tree question. I'll try to help, even if you are from south of the (state) border! First, can you send some photos? Second, Zone number is helpful but these trees can withstand far colder winters. How cold did it get there last year? Third, when it comes to mildew, it's a combo of temps and precipitation that 'count.' And you'll get more fungal infections on leaves that are in the shade. Any long-term effects, or just ugly? Whether you should amend soil depends on what is there. Have you measured soil pH and/or nutrients? (Test kits are cheap.) What type of soil--as in mostly clay, mostly sand, mostly silt or some combination? You can do a simple test by looking up 'soil texture test.' The texture of the soil gives you information about the tree's water needs. If it's sandy, water motors through, taking a lot of nutrients with it. If clay, it's either solid rock when dry or mud when it's wet. Both are hard on plants. You can help any soil by adding organic matter (aged compost), but you don't want to disrupt tree roots--and maples have lots of them near the surface. Just adding compost near--not touching--the trunk will, with the help of water and the trillions of microbes that live near your tree, eventually transport vital nutrients and matter to create pores (for water and nutrient transport) for any plant. I'm away from computer and can't cut and paste link, but OSU has a great publication on improving soil by adding organic material. Google it. Worth its weight in gold! Hope this is helpful. Good luck!