Prepare the nasturtium bed in early spring by rototilling it at least 6 inches to loosen and aerate the soil. Choose a location with poor, sandy soil if possible -- nasturtiums will not bloom well in rich soil. Resist the temptation to incorporate organic matter or fertilizer into the bed.
Check the temperature of the soil with a probe thermometer. Sow nasturtium seeds once the soil has warmed to 55 to 65 degrees Fahrenheit. Plant seeds at 2- to 3-inch intervals, 1/2 to 1 inch deep in the soil. Watch for emergence seven to 10 days later. Water seedlings when the soil is dry to the touch.
Harvest nasturtiums in the coolest part of the day, after the morning dew has evaporated. Choose flowers that have just opened. Pick just one or two and sample them before harvesting a large number of flowers -- nasturtiums should have a spicy, peppery flavor. Store flowers in the refrigerator immediately after harvesting and use within a few hours.