From our perspective as marigolds, the single most critical factor dictating your planting time is soil and air temperature. We are tender annuals, meaning we cannot survive a frost. Our cellular structure is not built to withstand freezing temperatures; ice crystals form within our tissues, causing irreversible damage and death. Therefore, the absolute rule is to plant us outside only after all danger of frost has passed in your local area. You must consult your local frost dates as a starting point. For us, the soil temperature is equally vital. We struggle to establish our root systems in cold, wet soil, which can lead to rot, stunted growth, and increased susceptibility to disease. We thrive when the soil has warmed consistently to at least 60°F (15.5°C) or above.
While your calendar provides a guideline, we plants respond to the actual conditions in your garden. The date of the "last frost" is an average, not a guarantee. You must observe the environment. Is the soil still cold and soggy to the touch days after a rain? Then it is too early for us. Have night temperatures been consistently staying above 45°F (7°C)? This is a very good sign. Another cue we respond to is the lengthening daylight of late spring. More hours of strong sunlight provide us with the energy we need for the vigorous growth you expect. Planting us when the days are too short and the sun’s angle is too low will result in weak, leggy seedlings straining for light.
If you start us from seed indoors, a sudden move from the stable, protected conditions of your home to the harsh, variable outdoors is a tremendous shock. Wind can shred our leaves, and strong sun can scald us. To ensure our success, you must gradually acclimate us through a process called "hardening off." This involves placing our trays outside in a sheltered, partially shaded location for just a few hours on the first day, gradually increasing the time and exposure to direct sun and breeze over 7-10 days. This process allows us to build stronger cell walls and adapt to full sun and wind, preventing transplant shock and setting us up for robust growth.
Our planting time is not uniform across all gardens. In warmer regions (USDA zones 9-10), you can often plant us as early as March or April. In cooler northern zones (zones 4-5), you must wait until late May or even early June. Furthermore, you must assess your garden's microclimate. Are we to be planted in a raised bed against a south-facing stone wall? This "heat sink" will warm the soil earlier, allowing for a slightly earlier planting. Are we in a low-lying area where cold air and frost settle? Then you must exercise extra caution and plant us later. Always observe the specific conditions of the spot where we are to live.
