The long, warm days of July make it a good month for sowing crops that mature well before the first autumn frosts. This includes leafy greens such as arugula and kale, cruciferous vegetables like radish and turnip, plus summer squashes, cucumbers, and pumpkins. July is also a good time to plant out established starts of winter cabbages that were started from seed earlier in the spring, or even to sow seeds of winter squashes and other cold-tolerant veggies such as bok choi and chard.
While it may seem a bit late to sow lettuce in July, heat-tolerant cultivars such as 'Salanova' and 'Green Star' can produce well into fall when planted this month in zones 2 through 7. In cooler climates, midsummer planting gives the elongated roots of carrots and parsnips time to sweeten before harvesting. Parsnips, especially 'Albion' and 'Warrior', are also frost-hardy and will keep producing into winter if allowed to endure some light frosts, which triggers the roots to accumulate more sugar.
If your garden has ample shade (which is not an issue in most regions), then 'Sora' or 'Pink Beauty' radishes can be harvested throughout the summer for crisp August salads and sandwiches. They are easy to grow and quick to mature, requiring only consistent moisture. This is a great crop to use for succession planting, as it grows quickly and can be seeded a few times throughout the season. Leeks are another cool-season veggie that can be seeded in July, though they need a long growing season to reach maturity before the frosts of November.