Answer: August is not really the best time to plant shrubs or lawn; the best time of year to plant evergreens is in the spring. However, you could try replacing your arborvitaes in September when the heat of summer is over. And, surprisingly, the best time of year to plant grass is in the fall.
Dead branches can be removed as soon as they occur. I should mention that Arborvitaes normally tend to show some noticeable browning and foliage loss at the interior of the plant in the fall. Also, arborvitaes planted in excessive shade will begin to grow thin and sparse due to lack of light.
I am not certain what the best treatment for your lawn would be. If the area is very shady, you may want to consider using a shade tolerant ground cover instead of lawn grass. (Grass needs sun all day or for at least half a day to stay healthy.) There really are no magical solutions to planting a lawn. The soil needs ot be well prepared and then the area needs to be kept evenly moist while the seed germinates and becomes established. The specialty lawn grasses such as zoysia are not well suited to your area, basically your winters are too cold for them and your growing season is too short.
Sand would need to be worked into the soil or removed, and in any case a generous amount of organic matter such as compost is usually helpful when trying to plant grass. I would strongly suggest you work with your Penn State cooperative extension to run some basic soil tests to check fertility and soil pH, evaluate the growing conditions where you are wanting to plant, and consult about the ant problem as well.
They will be able to help with the soil testing and interpreting the results, and should be able to recommend the best variety of grass to plant or may have other suggestions based on a more detailed understanding of the growing conditions in your yard. Also, if a chemical control is needed for the ants, they will have the most up to date information on what to use and how/when to apply it correctly for maximum results.
I hope this helps you evaluate the situation and get the advice you need.
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