Calendula

Calendula occupies a timing niche most other flowering annuals can't fill. It germinates and grows best in cool soil — 50 to 65°F — and will bloom heavily through spring before going quiet in midsummer heat, then often revive in fall once temperatures drop again. That makes it most useful at the beginning and end of the season, when the garden otherwise has little color. In mild-winter climates, it can bloom nearly year-round.

Direct sow seeds about 2 weeks before your last frost — calendula can handle light frost as a seedling and germinates best when the soil is cool. Press seeds about a quarter inch deep and keep them moist. Germination typically takes 5 to 14 days depending on soil temperature. Thin to 12 inches once seedlings are established. Calendula doesn't transplant poorly, but direct sowing takes advantage of the cool-season preference and is generally the better approach.

The petals are genuinely edible — they have a mild, slightly bitter flavor and add color to salads, rice dishes, or egg yolks if fed to chickens. The Resina variety has a higher resin content and is the standard for medicinal preparations and salve-making. Pacific Beauty is better for the vase and has large, flat flowers in orange and yellow tones. For cut flowers, harvest when buds are about three-quarters open; the flowers will continue to open in water.

Powdery mildew is calendula's most common problem and tends to appear when warm days are followed by cool, damp nights — a pattern common in spring and fall. The white coating starts on the lower leaves and moves up. It doesn't kill the plant outright but weakens it and reduces bloom. Spacing plants at least 12 inches apart and watering in the morning helps. When mildew appears heavily on established plants, removing the most affected leaves and cutting back lightly can sometimes bring a second flush of cleaner growth.

Calendula self-sows willingly, and in a garden where the seeds can reach bare soil, you may find it returning on its own in following years. This is one of its best qualities — let a few flowers go to seed deliberately, and the plant handles its own replanting. The hooked, curved seeds are easy to collect and remain viable for two to three years stored in a cool, dry place.