Water, water, water! Check sprinklers and drip systems to make sure that everything is working correctly. Check the soil moisture of your containers daily. If they are too demanding, use bigger pots next year; also go for glazed and not plain terra-cotta.
Dry weather makes it easier to keep up with the weeds, at least. Weed once, weed well, and then put down mulch (if you haven’t already).
Dig and divide crowded spring-flowering bulbs when the foliage dies off.
It’s really too hot, and the plants are too far along, to divide and/or transplant perennials – but if you absolutely must do it, work in the evening when it’s a bit cool, and keep the roots covered with moist soil the entire time. Water the new divisions daily until they are established.
Keep up with deadheading to encourage more flowers, especially on annuals.
Fertilize your roses each month during the summer. Deadhead regularly and keep an eye out for mildew, aphid, black-spot or other problems.
Deadhead annuals to keep them flowering. Deadhead perennials to encourage rebloom and to discourage heavy seeding.
Feed blooming annuals at least monthly to keep them producing flowers. Feed potted plants twice a month.
Raspberries: after harvesting summer-bearing varieties, cut spent canes back to the ground. Leave new green canes; tie them up when they are tall enough. On everbearing raspberries, cut out only the upper half of each cane that bore fruit this year.
Pay attention to climbing roses, clematis and any other plants you are growing on arbors or structures. They will need periodic training, re-tying and the occasional judicious snip.
If you have been pinching back your mums this summer, mid-July is the time to stop so they will be able to develop flower buds for the fall.
Stake your dahlias! To produce the largest flowers, the main stems of dahlias should be kept free of side shoots, allowing only the terminal bud to develop. This is crazy-obsessive but I’m just sharing it with you in case you are a competitive gardener.