Answer: The best times for planting are early spring beginning when the ground can be worked (not frozen, not too wet) through about mid May, and then in the fall. July and August are the worst times to plant because the weather is usually so hot and it tends to be dry or suffer dry spells. It is better to plant your plants now than try to keep them in containers for the summer.
I hope you have kept your plants watered while they are waiting to be planted, if not they may already be stressed. At planting, loosent the soil over a wide area and about as deep as the container. Loosen any encircling roots and plant at the same depth as it grew in the container. Water thoroughly to settle any air pockets.
After planting, mulch with two to three inches of organic mulch in a flat layer over the root area. Do not let the mulch touch the stem or trunk. Add more mulch periodically to maintain that depth.
Water as needed to supplement rain so that the soil stays evenly moist but not sopping wet or saturated, and never dry. 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 deep and encourages deep rooting. After watering, wait a few hours and then dig down to see how far the water went; it can be surprising.
The Japanese maple and PJM rhododendrons will need protection from winter winds and baking hot sun, usually these do best planted in bright dappled light all day or possibly on the east side of your house so it has afternoon shade. The other plants would do well in sun all morning or sun all day. The gold spirea and barberries can handle afternoon-only sun.
I hope this helps.
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