Answer: Both of these plants grow best in a somewhat acidic soil that is humusy and organic, it should also be evenly moist yet well drained. This means damp like a wrung out sponge, not sopping wet or saturated.
To know if you need to water, dig into the soil with your finger. If it is still damp you do not need to water yet. When you do water, water slowly and let it soak in deep to encourage deep rooting. Apply the water at the root area, not to the foliage. It is better to water deeply less often than to sprinkle lightly every day. After you water, wait a few hours and then dig down and see how far the water actually went; sometimes this can be surprising. It is probably best to water early in the morning, but if you are applying the water slowly to the soil surface such as with a soaker hose you can also water in the evening, but try to avoid wetting the foliage when you water as this can encourage some disease problems.
One sign of overwatering can sometimes be foliage problems such as browning. However there can also be disease/pest problems that could cause browning and other physical causes can cause browning as well.
I am going to guess that the white spots on the maple are some sort of chemical residue or possibly mildew, these can usually be literally washed off with water from the garden hose or by a hard rain. Powdery mildew can just appear in certain weather conditions.) However it is very hard to diagnose without seeing the plant. Since these are new plants I would suggest you contact the supplier and the installer for advice as soon as possible. Good luck with your new plants.
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