Answer: Japanese maples are naturally slow growers. Keep in mind that a new tree will devote much of its energy to becoming rooted and established in the new location. The best care you can give is to water correctly so the soil stays evenly moist, and mulch so it stays cool.
There is no set schedule for watering, it depends on your soil type and on the weather. Your goal in watering is to keep the soil evenly moist like a wrung out sponge, not sopping wet and not dried out. To know if you need to water, dig into the soil with your finger. If it is still damp, do not water yet. When you do water, apply it to the soil surface and water thoroughly and slowly so it soaks down to the deeper roots. After watering, wait a few hours and then dig down to see how far the water soaked in; it can be surprising.
Using an organic mulch several inches thick over the root area will help reduce watering needs as well as keep the soil cool in summer and feed the soil gradually as it breaks down over time. Apply it in a thin layer about two to at most three inches thick, no deeper. Spread it out flat over the root area, do not allow it to touch the bark or trunk of the tree.
The organic mulch will help enrich the soil. You can also topdress with a good quality compost once or twice a year. If you also want to fertilize, use a slow release granular fertilizer such as Hollytone. Read and follow the label directions for how much to use.
I am not certain what type of flies are in your garden. If they are a problem, you might consult with your local county extension to obtain a specific identification of the insect and based on knowing that, determine how to proceed. You would need to know what they are before you can figure out how to control them. If a chemical control would be effective, they will have the most up to date information on what to use and how/when is best to apply it for maximum results.
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