As soon as 21 days from sprouting, you can harvest flavorful radishes unlike anything from the supermarket. Radishes are some of the fastest and easiest vegetables to grow, making them a satisfying pick for new gardeners. They’re great for containers, too. A cool-season crop, radishes should be sown in early spring or late summer for a fall crop. The trick is to pick these quick growers before they pass their prime. The best way to determine the right harvest time? Pull one and do a taste test!