If you are growing for stems and blooms, plan to pinch to get a more robust and bushy plant. For garden, plants can be planted 6"-12" apart; in the field grown plants should be planted a minimum of 8" apart allowing the plant more space to grow both upward and outward. Plant Marigolds deeper than usual - they will send down additional root systems from the buried stem. Marigold like it warm - 79-90F through the day with nights around 68F. This means they are classically grown in Summer months, in full sun and suitable for most zones. While marigolds are quite easy to grow, keep an eye out for borers, bud worms, leaf chewers, spider mites and thrips. Potential diseases include alternaria, blight, botrytis, leaf spot, phytophthora and pythium. Disease often arises from soggy soil and wet leaves, so planning for lots of sun should keep these pests away.