Can Marigolds Grow in 60 Degrees?
- Marigolds need warmer temperatures while germinating and as they develop roots after being transplanted. ACES says African and French marigolds germinate in three to five days if nighttime temperatures are 75 to 80 Fahrenheit. For about 10 days after being transplanted, the nighttime temperature should be a minimum of 65 degrees Fahrenheit. Then nighttime temperatures can be dropped as low as 60 degrees as long as daytime heat is maintained at 65 to 72 degrees.
Similar to homeowners, who turn down the thermostat at night, some greenhouses are trying to control costs by decreasing nighttime temperatures. But in an article published at the "Greenhouse Grower" magazine, MSU says that at least for commercial growers, this may be counter productive, because it increases the amount of time necessary to prepare marigolds and other flower sets for outdoor planting. Cooler temperatures slow growth. - Unlike greenhouses, which must get product to market quickly, home gardeners can be more relaxed about the growth schedule of their marigolds. SMU says there are some benefits to slower growth, such as plants producing more blooms at first flowering. It notes that since cooler nighttime temperatures can result in an extended stay in the greenhouse, which can strengthen plants due to a longer period for photosynthesis before sale.
- When starting plants indoors, gardeners can compensate for cool nighttime temperatures through increased lighting. In northern greenhouses where indoor lighting isn't powerful, the amount of daily light plants receive in late spring is five times the amount they get during winter. An increase in supplemental lighting can speed up flowering and improve plant health. Home gardeners can apply these principles when setting up a grow station indoors.
- Homeowners who have become accustomed to a cooler nighttime thermostat setting may be reluctant to turn up the temperature for germination. The University of Illinois Extension says to place the trays of marigold starts in a part of the house where temperature can be maintained and where watering spills won't be a problem. It says to arrange several 40 watt cool white fluorescent tubes about 6 inches apart and 6 inches above the tray of starts. To increase temperature, it suggests arranging a plastic tent over the lights and trays to increase heat. The flowers need at least 12 hours of light a day until outdoor transplanting.
- Once well established, marigolds can tolerate cooler outdoor temperatures, such as 60 degrees Fahrenheit. They are considered "half hardy" annuals, which means they continue blossoming through cool autumn temperatures when other annuals have already ended their growing season.