When to sow French marigold?

French marigolds are half-hardy annuals that cannot tolerate frost, so timing is crucial. Sow seed outdoors from late April onwards, once all risk of frost has passed and the soil has warmed to at least 10°C. In colder areas or for earlier flowers, start seed indoors in March or early April, sowing thinly in trays or modules at around 18–21°C. Germination usually takes five to seven days. Transplant seedlings outdoors in May or early June after hardening them off for a week. Choose a spot in full sun—French marigolds flower most prolifically with at least six hours of direct sunlight daily. They tolerate a wide range of soils but perform best in well-drained loam or sandy soil. Heavy clay can lead to root rot, so dig in plenty of grit or compost to improve drainage if necessary. The soil doesn't need to be especially fertile; in fact, overly rich ground encourages leafy growth at the expense of flowers. Prepare the bed by removing weeds and raking to a fine tilth. Sow seed thinly, covering with no more than 5 mm of soil—French marigold seed needs some light to germinate well. Space plants or thin seedlings to 20 cm apart to allow good air circulation and prevent mildew. If planting out pot-grown plants, set them at the same depth they were growing in their containers. Water gently after planting to settle the roots, but avoid waterlogging. A light mulch of compost around the base helps retain moisture and suppress weeds, but keep it clear of the stems to prevent rot. French marigolds establish quickly and usually begin flowering six to eight weeks after sowing.