Q.Ever Autumn Japanese maple
Tree planted with lots of leaves October 2017. Not leafing out as of June 2018. I scratched the branches and see green. Overwatering, underwatering?
That's not good. But if you see a green growing layer under the bark, all may not be lost. Get some water to it right away, today, unless you think you have overwatered and you find the soil at the base of the tree to be soggy wet. I have seen both conditions cause decline in Japanese maples.
Underwatering is the most common problem that see with Japanese maples in Marin and the Bay Area, they are not drought tolerant, they need weekly irrigation, especially this time of year in San Anselmo, it can be quite hot. Yes I know the area well, and it appears that you are in the hills, and the maple is planted under or next to coast live oaks with a Mexican fan palm next to it.
Drip irrigation systems are often inadequate for a maple that needs frequent deep watering. It's best to drench it once a week with a hose end, then let it dry out some before the next watering.
There are disease conditions that can affect Japanese maples, Verticillium wilt is one, but it is not as likely to be the case with your tree.
If by chance you had your oaks sprayed with Agrifos fungicide for prevention of Sudden Oak Death, overspray or drift of the salty material can affect the foliage.
You have a built in problem with incompatible plantings. The native oaks should not be watered frequently, once a month at the most or not at all. The palm can exist on a similar irrigation program. But the maple cannot, it needs more water than the other trees.
