When to sow Zinnia?

Zinnias are half-hardy annuals that must be sown or planted after all risk of frost has passed, making May and June the ideal planting window in temperate Europe. They demand full sun and will produce weak, leggy growth and fewer flowers in shade. Choose a sheltered spot if possible, as their tall stems can be damaged by strong winds. Prepare the soil by digging in well-rotted compost or garden manure a few weeks before planting. Zinnias thrive in loam—fertile, well-drained soil that holds moisture without becoming waterlogged. If your soil is heavy clay, work in grit or sharp sand to improve drainage; if it's very sandy, add organic matter to boost water retention. Rake the bed to a fine tilth and remove any weeds. You can sow zinnia seed directly outdoors from mid-May onward, once soil temperatures reach around 15°C, or plant out young plants raised indoors or bought from a garden centre. Sow seed thinly, about 1 cm deep, in drills or scatter in patches, then thin seedlings to 30 cm apart once they have two or three true leaves. If planting out young plants, space them 30 cm apart in rows or groups. This spacing allows good air circulation, which helps prevent mildew, and gives each plant room to develop its full spread of 25–40 cm. Water gently but thoroughly after planting or sowing to settle the soil around roots or seeds. Avoid overhead watering if possible, as wet foliage encourages fungal disease. Apply a 5 cm layer of organic mulch around the base of plants once they're established to conserve moisture and suppress weeds, but keep mulch clear of stems to prevent rot.