Plant sweet corn anytime in May. Early May sowing is fine for asters, alyssum, calendula, centaurea, viola, scabiosa, mignonette, dianthus, cosmos, snapdragon, gypsophilia, nasturtium, phlox, and verbena. Green beans can be planted around the 10th.
If you want to plant lettuce, consider varieties like Ruby, Matchless, or Oak Leaf. They are slower to bolt in June heat. Plant squash seeds beginning the second week of May. Tomato, pepper, and eggplant seedlings can be set out beginning the 15th. Be ready to cover them at night in case of late frost.
Plant seeds of heat–loving plants like melons on the 22nd or later. All tender plants can be sown at that time. Keep seeds continually moist, but not soggy, until seedlings are up. Consider using a mulch to cut down on watering and weeding.
Warm days near the end of May make lawns thirsty. Most grasses need one inch of water per week except in the hottest weather. It is better to provide 1/2 inch of water twice a week than small amounts daily. Grass next to curbs or sidewalks may need extra waterings.