Chrysanthemums planting and aftercare
Newly propagated young plants need to be hardened off in April by being placed in a coldframe.
Plant out in mid-May, once the risk of frost has past. Space them 45cm (18in) apart.
Choose a sheltered sunny position; ideally improve the soil by digging-in well-rotted organic matter such as homemade compost during the winter at about 10kg per sq m (25lbs per sq yd), usually one to two bucketfuls per square yard or metre. Then fork in a dressing of general fertiliser (100g per sq m (4oz per sq yd) of grow more or blood, fish and bone) towards the end of April. A 'top dressing' of nitrogen-rich fertiliser is often applied in June to encourage growth (35g per sq m (1oz per sq yd) of sulphate of ammonia, or for organic gardeners, 70g per sq m (2oz per sq yd) of dried poultry manure pellets).
- Depending on habit and flower type, plants will require pinching out and staking. Pinching out (stopping) the growing points in late May or early June encourages branching.
- Large single blooms (often called 'disbuds') are encouraged by maintaining the main central bud and removing all side buds and shoots so that only the terminal flower bud on each shoot remains.
- Spray cultivars can produce a more even spray formation by removing the terminal flower bud.
- Flowering times and optimum stopping times can vary according to the cultivar, seasonal and regional variations. Further details can be found in the catalogues of specialist growers.
Cutting back and overwintering
- After flowering, cut back the main stem to about 20cm (8in) to produce what is known as a stool or rootstock.
- On average early chrysanthemums have a hardiness rating of H3 (which has a minimum temperature of -5°C) so, in mild areas, they can be left outside over winter, with a good covering of coarse organic matter such as homemade compost or bark chips as a protective mulch. A well-drained site is preferable.
- On cold, exposed or badly drained sites, lift and store the stools over winter in frost-free conditions, such as a frost-free greenhouse or a cool conservatory.
Preparation for overwintering
- Lift the shortened plants from the ground or remove from their pots. Ensure that the surplus soil is shaken from the roots.
- Tidy up the stools by removing green shoots and leaves, leaving just the stems shortended to 8cm (3ins). Then label each stool as they will all look similar at this point.
- Place the stools in a shallow tray on top of a 5cm (2in) layer of multi-purpose compost, ideally peat-free, and then give the roots a light covering of compost once packed in the tray.
- Do not water them in and keep them cold but frost free over winter, such as in a heated greenhouse or cool conservatory.
- Keep the compost just moist through the winter.