Growing Chrysanthemum Plants Outdoors
With the Koreans, Pompons, Singles and Sprays it is necessary to remove the deadfrom your chrysanthemum plants from about the middle of August. This will encourage new shoots to grow and so prolong the flowering period.
Before doing this job I like to tie a label to the base of the stem of each variety. On this I write the name, colour, type and height to which it grew. By doing this, you have all the details you need when planting again the following year.
When the chrysanthemum plants have finished flowering, which will be about mid-October, the stems can be cut down to within 9 to 12 in. of the ground. It is not important to do this job immediately after flowering – very often I leave it until the end of November and the plants do not suffer in any way.
Lifting and Boxing
After cutting down the stems of the chrysanthemum plants, the roots should be lifted carefully and all theshaken off them. Any shoots that are growing from the base of the stems are best cut out. There is always a temptation to leave these, thinking that they will be all right for cuttings in the spring, but they do not make good ones.
If possible, it is a good idea to give the stools (the name given to the chrysanthemum plants after they have finished flowering) warm-water treatment before boxing them up. This is to control chrysanthemum eelworm which may be present in the stools. If symptoms of attack have been noticed during the season then this treatment is strongly recommended.
The stools should first of all be washed clean of soil and then immersed in water at a temperature of 46° C. (115° F.) for five minutes, or, in the case of the Loveliness varieties, 43°C. (110°F.) for 20 to 30 minutes. The higher temperature is a more recent recommendation and involves less risk of damage to more sensitive varieties. The Loveliness varieties may be damaged, however, unless the plants are, apart from the eelworm damage, reasonably strong and healthy. When the stools are removed from the water, they are plunged at once into cold water and then boxed up.
A few varieties are rather sensitive to this treatment, while others respond well by producing many healthy, vigorous shoots which make ideal cuttings.
I would advise the amateur gardener to invest in the proper equipment for this task, so that the water is heated to exactly the right temperature. If the water is heated above the recommended temperature, then the stools will certainly be killed, and if it is not hot enough the treatment will be ineffective.
Whether the stools have been treated or not, the next stage is to box them up into deep boxes. I use a compost consisting of equal parts loam, peat and coarse sand, but with no fertiliser. Place about 1/2 to 1 in. of compost in the bottom of the box, pack the stools in close together and cover the roots with more soil. It is important that the stools should be kept only just moist during the time of dormancy.
Housing Chrysanthemum Plants for the Winter
If the weather is reasonably mild after boxing the stools, your chrysanthemum plants can be placed outside under a warm wall. In severe weather they are best put in cold frames and the lights covered with straw or matting during frosty spells. Alternatively, the boxes can be placed in the frames straight away. Except during frosts, give the stools some ventilation. If you have a heated greenhouse the boxes are best transferred to this in mid-January to encourage shoots to grow for the purpose of taking cuttings. If a greenhouse is not available the stools can remain in the frames, if well protected during hard weather.
When the stools are brought into the greenhouse always place them on the staging where they will get the maximum amount of light to encourage sturdy shoots to develop. Spindly and ‘drawn’ shoots do not make good cuttings.