People ask me daily if it is Okay to plant in this heat we have been experiencing. My first comment is an enthusiastic “YES”. I go on to explain that most plants that have been surviving in black plastic nursery pots will be 100 times better off in the ground where the soil will insulate it and give it room to spread out. They will not be as likely to dry out in between watering. Most newly planted items are given a dose of some starter fertilizer and have organic amendments added around them when planted. As long as they are given sufficient water, they will reward you as they thrive and grow.
Watering will be the biggest factor in determining if you plant stresses from the transplanting or not. I can tell you that the plants in nurseries are watered twice a day in this heat. You should do the same and then gradually taper down to once a day and then maybe every other day for the remainder of the growing season. It would be wise for you to plant in the early morning or in the evening when it cools, as this is going to be the least stressful for you and the plants!
Plants that do not get their water needs met will let you know. They will start with wilted leaves and if seen and watered soon enough, they will recover. If not caught soon enough, the wilted leaves will get crispy. This can happen to the entire leaf or just to the edges. This does not mean the plant is dead. Many times, simply cleaning off the crispy leaves will help the appearance and the plant will replace the leaves within a couple of weeks. If a plant goes dry for so long that the branches or main stems also become dry and crispy, you can usually cut back the plant to healthy growth and it will grow back. With perennials, many can be cut down to the ground and they will grow back from the roots, as long as the root ball did not dry out completely.
I like to remind people that landscapers plant shrubs and trees almost all year long. They are experienced and familiar with the demands of the heat, but you can take the steps I mentioned above and plant to your heart’s content, even in the heat! Happy Planting!