When to plant
- Although chrysanthemums can be planted in spring or fall, those planted in late April or May are more likely to survive the following winter. Once flowers fade, prune plants back one-third to one-half of their flowering height; they should bloom again in fall. This applies only to spring-planted mums: those planted in fall won't have time to bloom again before it becomes too cold.
- If you buy garden mums in late summer for a fall display and don't want to treat them as annuals, plant them at least six weeks before the first expected frost so they can become established.
- Avoid siting plants in areas subject to cold, dry, north winds. Choose an area in full sun and away from street or other lights, which would expose them to too much light at night and thus inhibit flower formation.
- Plant chrysanthemums in moist, well-drained soil, at about the same depth they're grown in their pots. Dig in five to 10 centimetres of organic matter such as compost, composted manure or peat moss around the plants. Set mums 45 to 60 centimetres apart so they have room to develop. Keep them well watered. They're heavy feeders, so give them either a water-soluble or an all-purpose fertilizer (such as 10-10-10) once a month.
Encouraging new growth
- Rough up the root ball of a pot-grown (they are almost always sold in pots) hardy mum with your hand or cut some vertical lines down its sides to promote lateral branching of the root system into the soil.
- Although some newer cultivars don't require pinching, most mums will become tall and leggy if not pinched back. Here's how: Beginning in May, whenever a new shoot reaches seven to 10 centimetres tall, pinch it off using your thumb and index finger, leaving two or three leaves on the shoot. Fertilize plant and pinch back any tall shoots about once a month until mid-July.
- The first hard frost usually marks the end of the season for hardy mums. Once plants are dormant, remove the faded or dead flowers but do leave the stems. Studies have shown that mums survive the winter better if their stems are not cut back. New shoots will appear early the following spring.