How to Plant Rose Mallow Seeds Rose Mallow seeds require light to germinate, so be careful not to cover them when planting. Learn more about germination light requirements here. Prepare Rose Mallow seeds by soaking them in warm water for approximately 24 hours before planting. Nick the seeds with a sharp knife - this will aid your Rose Mallow seeds in germinating. Sow 3 -4 Rose Mallow seeds in a group, approximately 18-24 inches apart onto the surface of the soil, and compress firmly. Do not cover the seeds, as they require sunlight in order to germinate. Germination will take place in approximately 15-30 days. How to Care for Rose Mallow After the Rose Mallow has grown a few inches, thin to one plant every 36 inches. Water Rose Mallow regularly, and deadhead spent flowers to encourage additional blooms. Watering is especially important as the Rose Mallow establishes - ensure you water if you see any signs of wilting. Rose Mallow will self-sow if allowed to go to seed.