Common Name Marigold, African Marigold 
Genus  Tagetes
Species T. erecta
Family Asteraceae
Life Cycle  Annual
Tray Size  125, 210
Plug Care Harden off and plant out or bump up soon after receiving plugs. Plan for the plugs to arrive after last frost when the soil has warmed so that you are not holding them for an extended period of time. Rootbound and stressed plugs will flower prematurely and will fail to reach their full potential later in the season. Plant plugs slightly deeper in the soil as additional roots will grow from the buried stem. 
Netting / Staking Use 2 layers of netting to support these tall, top-heavy plants, especially in areas with wind and rain. Be careful when harvesting to not injure flowers and stems while removing them from the netting. 
Temperature Range Optimum daytime temperatures during growth are 79-90F through the day with nights around 68F. They can handle heat and are suitable for almost all growing regions. 
Spacing Spacing recommendations vary depending on whether they will be grown in a greenhouse or in the field, and as a disbud or a spray type stem. Typically, disbud stems can be grown closer together (4-5") and pinched field grown plants should be the furthest apart (8"). See the 'Coco Cultural Information' link posted below for a more detailed breakdown on spacing requirements. 
Soil Preference Marigolds are fairly heavy feeders, so the bed they are going in should be amended with compost and granular fertilizer before transplant. Heavier clay loam soil is ideal. Keep the soil evenly moist but not overly saturated. See the 'Coco Cultural Information' link below for a more detailed breakdown of fertilizer and nutritional needs. 
Day Length Short day, or day neutral, depending on variety.  Ideally given some time to establish vegetatively under long days before budding for larger, more productive plants. Plant in full sun.  
Pinching We recommend pinching at approximately 2 weeks after transplanting to promote side branching. Can be grown as a single stem disbud (side shoots removed) and spaced closely for the largest possible flower. If pinched and given more space, they are a cut and come again type plant. 
When to Plant Plant in the spring well after last frost when the soil has warmed, around the same time you would be planting zinnias and celosia. It is possible to plant a later succession, approximately 4 weeks later, to insure the availability of cutting material right up to frost. 
Harvesting For 'Chedi', Transplant to first flower takers 65-70 days under short day length and 70-80 days under long day length. This can vary depending on temperature and weather conditions. Flowering under short days will be on smaller, less productive plants. For local markets, harvest when the flowers are almost completely open. For storage and shipping, harvest when 50% of the petals have opened. Harvest in the afternoon for the longest vase life. 
Post Harvest Care Cut stems should be immediately plunged into cool water and should be re-cut if they are out of water for any length of time. The use of a hydrator and floral preservative will maximize vase life which is typically 1-2 weeks. Marigolds dry-store well. 
Diseases / Insects Typically marigolds are robust plants and aren't often plagued by insects or disease. Insect pests can vary by zone, but watch for borers, bud worms, leaf chewers, spider mites and thrips. Potential diseases include alternaria, blight, botrytis, leaf spot, phytophthora and pythium. Periods of saturated soil, cold weather and wet leaves will increase disease pressure. 
Bailey's Notes

Marigolds need no introduction to most of us, but perhaps they need to be introduced into your cut flower program! They are tall, easy to grow, long lasting and nothing fills out a summer mixed bouquet like a stem or two of marigolds. The scent is beloved by some and off-putting to others. 

Marigolds are very important in a number of cultures. They are often used in Indian wedding ceremonies. Marigolds are also very important in Mexican Day of the Dead celebrations. They are used in a number of other South Asian cultures as well. If you serve any of these communities there may be an unmet need to consider. 

Resources

Chedi Growing Information

Coco Cultural Information