The cultural programme for this section of thefamily is much the same as that for border . General advice on propagation, , staking, stopping and disbudding is largely common to both, but such variations of treatment as there are arise from the fact that greenhouse chrysanthemums are normally grown in pots and that their season of blooming is later — from late October to Christmas or even beyond. This means that some source of gentle warmth will be required in the greenhouse if blooms are to be safe after the end of October.
Propagate as for the garden types but start a little earlier — in January. When theare rooted, put the young plants into 3-in. pots and gradually harden off. As the roots grow and fill the pots, move the plants to larger pots, first to 5- or 6-in. sizes, using a slightly stronger mixture. John Innes No. 2 is best at this stage. Towards the end of May these pots will become full of root and a further move to 8- to 10-in. pots, containing John Innes No. 4, will be necessary. Using a short piece of old broom handle as a ramming stick, firm the soil as the plants are potted, finally adding a bam-boo stake to each pot and tying the plants to the stakes. Stand these final pots outside, generously spaced in lines on a sunny site, and secure the stakes to a strong wire run along the length of each row about I ft. from the ground and fastened to a strong post at each end.
During the summer watering is the most important job; do this carefully, letting the root system dry out almost to flagging-point between each watering.
About six weeks after the final potting, begin feeding with a fertilizer sold specially for chrysanthemums and continue until the buds begin to show colour. Either dry or liquid forms of fertilizer may be used. Bring the plants into the greenhouse at the end of September and after a week or so of full ventilation, regulate the ventilation and heating systems to maintain a dry, buoyant atmosphere at approximately 50° F. (10° C.). This temperature may be increased a little as the flowers reach maturity.
Alternatively, instead of putting the plants into the largest pots, put them out into the open ground at the end of May. Then carefully lift them in late September and plant them in old tomato beds in the greenhouse. This saves much labour in watering and is often successful, particularly with the dwarfer growing varieties which re-establish more quickly after root disturbance.
Buds will appear from mid-August to mid-September and, except in the case of American Spray varieties it is essential to reduce the buds to one per stem to get the finest results.
The time at which the buds are formed has some effect on the size and quality of the flowers, so adhere to the pinching dates given in the list that follows, or in specialists’ catalogues.
With the Christmas-flowering varieties it is usual to give two pinches, the first when the plant is about 9 in. tall and the other in mid-July.
Restrict the plant to four or five stems if top-sized flowers are required, but most varieties will carry from eight to 12 satisfactorily if quantity is the aim.