There are five popularly-grown types of border chrysanthemum — the incurved, the incurving, the reflexed, the pompon and the single. All are early flowering, and bloom, according to variety, from early August to late September.
Since chrysanthemums cannot be relied upon to come true from seed and are propagated by vegetative means, it is best to start growing them from rootedobtained either from a nursery-man or from a friend’s collection.
There are two principal ways of propagating chrysanthemums — by the division of roots or by the rooting of cuttings.
At the close of the flowering season, leave the plants for several weeks so that matured sap in the stems may dry back into the rootstock. Then, in late October, cut back the main stem of each plant to some 6 to 9 in. from the base. In some areas it is possible to leave the plants inthroughout the winter, but for the best results with modern varieties it is far better to lift them and put them under some slight cover to keep them from frost. It is not dry cold which must be guarded against, but dampness, which has a disastrous effect.
Lift the rootstocks carefully and shake off most of the soil. They are then known as stools. Wash them in a weak solution of Jeyes Fluid. If it is intended to divide the stools in the spring, do not prune the roots at all, and leave any small green shoots that may appear. If, however, cuttings are going to be taken later, or where a large number of stools have to be accommodated in a small space, it is quite safe to prune the roots back until the whole ball will pass through a ring of 4 in. diameter. Put the stools into a box of fresh soil, preferably John Innes No. l, covering the roots just a little deeper than they were in the garden. Place the box in a cold frame or unheated, and give only to keep the roots from drying out. Expose to full air at every opportunity in order to keep the plants dormant until the lighter days of spring. Once growth can be seen above the soil, give water according to weather conditions and the state of the stools. Slugs will be a constant danger, so take preventive action early.
In March, early to late according to district, take the stocks intended for divi-sion outside, and remove young growths from the outer portions of the stools, making sure that each growth has a number of roots attached. In the more sheltered districts these young plants can be put out into permanent quarters, but in exposed areas it is better to plant them out in boxes or protected nursery beds until they are stronger. Although the chrysanthemum is fairly hardy, young plants do not thrive in cold winds or when their roots are continually cold and wet.
Better results are usually obtained from cuttings. Stools intended for cuttings may be left in cold frames, or brought into a cool greenhouse during February. Slight warmth is helpful though not essential, and a temperature of 45 to 50° F. (7 to 10° C.) should be maintained. In all but the very favoured districts plants from cold frames cannot be propagated until March, but in a heated greenhouse cuttings can be taken from February to early April.
Prepare boxes or a bed of soil about 3 in. deep, using either John Innes No. 1 compost or a mixture of equal parts of soil,and sharp sand with a dusting of superphosphate mixed in. Since it is good practice to have the base of each cutting resting in pure sand, sprinkle about in. of dry sand on top of the soil before work begins; as the hole is made for each cutting the sand will trickle in.
With a sharp knife or razor blade carefully cut off the growths just below a leaf joint and trim them so as to make cuttings 2 to 3 in. long. Remove the lower leaves and insert the cuttings in the soil. The cuttings can be put in the boxes or the bed quite close to one another, but do not let the foliage overlap. To settle the cuttings in, water thoroughly using a can fitted with a rose. It should not be necessary to water again until rooting takes place three to four weeks later.
Since the cuttings have to live for a few weeks on their own sap it is essential to reduce evaporation from the leaves. This can be done by covering the boxes or bed with glass or polythene, but there is then the danger of air being excluded. A safer way is to stretch butter muslin a few inches over and above the cuttings. This keeps the air around them sufficiently close but also permits it to circulate.
Although heat is not essential, gentle bottom heat will hasten the process of rooting and lessen the risk of damping-off; in a cold frame the heat can be provided by a soil-warming cable.
The time the cuttings take to root varies according to conditions, but the signs are unmistakable. When there is a new green in the foliage and the growing point has obviously developed, working roots have formed. Thenceforth, each day for a week or so, expose the young plants to increasing periods of light and full air, then transplant them into boxes •I in. deep filled with John Innes No. 1 compost. Boxes are better than pots, particularly if the plants are left untended during the day, for the larger body of soil retains moisture longer and eases the watering problem. Lift the plants carefully with moist soil attached to the roots, which should be about 1 in. long, and set them -I in. apart in the new boxes. Do not make them too firm. Withhold water for a few days and at the same time shade the cuttings by means of paper supported on small canes and, when the weather is bright, spray water over the plants. This enables them to get the moisture they need without letting water penetrate to their roots.
Gradually admit more air. When the plants are firm and start to grow, those in the greenhouse can be moved to the frame.
The aim from that time until late April is to encourage firm growth and the development of a strong root system. Harden off the plants slowly, protecting them always from frost, heavy rain and cold draughts.
Keep an eye open for greenfly, and constantly bait against slugs. In the first week in May it should be possible to leave the frame lights off altogether to prepare the plants for their final move into the open garden on about May 10.
Since chrysanthemums bloom quite late for outdoor flowers, they may make flowerless patches in the border through-out the summer. This can be avoided by growing the plants in pots or nursery beds until, say, July, when they can be transferred to their permanent sites. The nursery bed is suitable for only the dwarf varieties, but even these are safer in pots, for transference from one bed to another can be risky.