Most of June is good for planting perennials, but it can get too warm at the end of the month. If the weather is unusually hot (over 85 degrees), your plants experience more transplant shock and that could set them back. Make sure they are watered, maybe three times a week until new growth appears. Then cut back watering to once a week, deeply. It is best to check daily for any wilting. 

Here are some other chores to keep in mind:

• Make sure any plants started (or purchased) in pots are planted in the ground by mid-June. If you divide and transplant this month, cut the plants back and keep them well watered.
• Keep up with your weeding. 
• Japanese beetle adults will be out this month. Be vigilant and knock them off into a bowl of soapy water early in the morning. If Japanese beetles can’t be controlled by hand picking, spray with neem oil twice a week.
• Cut back any flowers that bloomed in early spring that may be flopping or looking straggly and cut off dead or yellowing leaves.
• Any plants that will bloom later in the summer or fall can be pinched at this time to create additional growth and to control excessive height. Joe-Pye weed is a classic example of something that can get out of hand. By pinching, I mean simply removing the actual growing tips, including one set of leaves on each shoot. Using your fingers is usually the best way.
• Mums (Chrysanthemum spp.) should be pinched or cut back early in the month. Pinch off any buds that are showing at this time. In the Philadelphia area and other zone 6-7 areas, pinching should end before July 1. Mums need about a month to set new buds after pinching.
• Cutting back asters at the same time. They will fill out and although they will flower a bit later in the fall, they’ll be less floppy and scraggly. Similarly, goldenrod (Solidago spp) will benefit from cutting back, which will reduce their height and create a bushier plant.
• Place supports and stakes now for plants such as delphinium, even if they won’t be needed until later in the summer. Thin delphinium when they are 6” tall so as not to crowd each other out. They are heavy feeders and can use a bit of fertilizer at this time. A slow release, granular, balanced fertilizer is best.
• If you have roses, don’t neglect to cut a bouquet for inside the house. It will strengthen the plant and promote healthy growth. Deadhead the ever-bloomers. 
• Yarrow (Achilla millefolium) will bloom all summer if you keep it deadheaded. Cut plants back by 1/2 early in the month and you will get shorter, self-supporting plants. Caution: If you cut back after the buds form, you will not have any blooms until next season.
• Cut off yellowing leaves of hollyhocks (Alcea rosea) and any leaves damaged, diseased or eaten by insects.
• Deadhead peonies immediately after blooming.
• Prune coneflower (Echinacea spp) early in the month only if you want to postpone blooming until late in the fall.
• Native sunflowers (Helianthus spp) can be cut back this month; trim only some of them to produce plants of different heights. Blooming will still happen all summer into fall. Heliopsis helianthoides can also be cut back, but blooming will be delayed until later in the summer.
• Candytuft (Iberis sempervirens) should be finished this month. Shear back the entire plant and keep watered through the rest of the summer.
• Deadhead Shasta daisy (Leucanthemum X Superbum) now and continually. Blooms will continue into the fall.
• Do you grow Indian cup plant (Silphium perfoliatum)? Cutting back the stems now will make the plants stronger. They will still bloom all summer and provide seeds for the finches.