Chrysanthemums grow up to three feet tall and up to two feet wide. Mums (Chrysanthemum flowers) can grow rapidly from seeds in just 10 to 15 days. Feed fortnightly with a high potash soluble/liquid plant … Space your mums … Hardy Chrysanthemum Care . From late spring to mid-summer, pinch back the tips and flower buds on all shoots to make the plant bushier and prepare it for a dramatic fall show. Growing in containers. This gives the plants the most time to establish root systems and gain strength before the first frost. For optimal blooming, the plants should be fertilized regularly throughout the growing … Plant Chrysanthemums Early. Plant your perennial mums in the spring. Mums … Ensure you use a good potting compost and keep the plants well fed throughout summer and early autumn. Growing chrysanthemums indoors. Some chrysanthemum varieties should ideally be grown indoors – in a greenhouse or protected growing space of some kind – and will then flower from mid/late November … However, seeds must be planted at the right time of year and kept under appropriate conditions to perform their best. Spray chrysanthemums are perfect container plants – providing masses of colour to brighten up patios and other areas. Plant mums as soon as the soil warms in the spring.