Marigolds thrive in full sunshine and can often withstand very hot summers. Though they grow in almost any soil, marigolds thrive in moderately fertile, well-drained soil. Prepare the soil by digging down about 6 inches to loosen it. Remove stones. Optional: Add some granular fertilizer in the planting hole. A 5-10-5 works fine. Sow them directly into the garden once the soil is warm. You can start seeds indoors but they germinate so easily outside that there’s really no advantage. Marigolds sprout within days in warm weather and plants bloom in about 8 weeks. Sow seed 1-inch apart. While still small, thin the seedlings. Space French and Signet types 8 to 10 inches apart. Larger American varieties should be at least 10 to 12 inches apart. After planting, thoroughly water each plant. Separate seedlings when they are about 2 inches tall. Plant them in flats of loose soil, or transplant them into the garden. If planting in containers, use a soil-based potting mix. Either mix in slow-acting granular fertilizer at planting time or plan to water in diluted liquid fertilizer periodically. Take care to space properly; marigolds grown in containers can become crowded.