Answer: You can still plant container grown plants. Make sure to water them before you plant, then water thoroughly right after planting to settle any air pockets. Then mulch with several inches of organic mulch to help keep the soil evenly moist like a wrung out sponge while they become established.
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, water slowly and thoroughly so it soaks down to the deep roots. After watering, wait a few hours and then dig down to see how far the water soaked in; sometimes it can be surprising.
It is not too late to fertilize your lawn, however additional fertilizer may not be needed if it was done earlier this spring. The best thing to do is to run some basic soil tests and check the fertility and soil pH levels. Then you would fertilize and/or add lime based on the test results.
If your lawn is brown, it may be that it needs water rather than fertilizer or it may have a pest or disease problem. I would suggest you consult with your local county extension to trouble shoot the lawn issues. They should also be able to help you with the soil testing and interpreting the results.
Enjoy your new home!
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