Year-round Production of Chrysanthemums in Japan By JOICHI KAWATA Researcher, Laboratory of Floriculture, Horticultural Research Station Chrysanthemum is a national flower in Ja­ At present they have become one of the pan as well as cherry blossoms. Though it most important flowers for cut flowers as well seems to have originated from China, the as potted plants comparable to roses, carna­ Japanese have deeply admired it and bred so tions and cyclamens. many varieties with various types of flower They can also be grown abundantly in during the Tokugawa era (17th- 19th century) Hawaii and Formosa under the subtropical as we can see them now. These varieties were climatic condition where the day-length and introduced to Europe in the 17th century, and temperature are suitable to flowering all year then to the United States. round, even if supplementary light is applied Table 1. Classification of chrysanthemum varieties in Japan based on the responses to temperature and photoperiod (Okada, M., 1963) Respone to photoperiod No. of Group Group Flower bud Flower bud Response to temperature initiation development and flowering Usually flower bud initiation is acomplished, provideed that minimum temperature is above I Autumn flowering Short day Short day 15°C. and flower bud development and flower- ing are not inhibited by high temperature. Flower bud development and flowering are II Winter flowering Short day Short day inhibited by high temperature. Usually flower initiation is accomplished m August flowering Day neutral Day neutral about 10°C. Flower bud initiation is accomprished, pro- vided that minimum temperature is above 1s•c, similarly to autumn flowering chry- IV August flowering Day neutral Day neutral santhemums. Usually flower bud develop- ment is inhibited by lower temperature and flower bud is differentiated into crown bud. Same response as August flowering chry- V September flowering Day neutral Short day santhemums as far as temperature is con- cerned. Same response as autumn flowering chry- VI Okayamaheiwa type Short day Day neutral santhemum as far as temperature is con- cerned. - 23 - for some duration after cutting or planting to a) Cultivation of autumn flowering varie­ promote vegetative growth to some extent. ties in the open. Temperature and photoperiod have proved Cutting should be done from the beginning to be important factors in the control of flower of May to the Middle of June. After rooting initiation and its development in crysanthe­ they are provisionally planted in bed by the mum. Consequently the time of flowering can time their roots are well developed. And then be regulated by artificially controlled tempera­ they are again transplanted to bed. One week ture and day length. By using normal autumn after, starting stage of growth, their terminal or fall flowering varieties, satisfactory blooms growing point with a few unexpanded leaves can be produced at any season of the year. are removed. When the date of pinch is early, In the United States and Europe, year round the branch will produce crown buds which production of chrysanthemum is only carried will not be able to develop normal flower. out by controlling temperature and day-length, These crown buds should be removed to pro­ while in our country it is also done by the duce normal flower buds. same method on a larger basis, and on the The date of flower initiation is from the other hand by using various ecological types middle of August to the beginning of Septem­ of which responses to temperature and day­ ber according to variety. Flowering date is length are different from type to type. These from the beginning of October to the end of varieties have been introduced by some breed­ November. ers in Japan who can be proud of their b) Cultivation of winter flowering varieties. achievement, admired by the world's horticul­ The photoperiod requirement of this type of turists. varieties is the same as the autumn flowering According to an extensive study conducted varieties, while high temperature prevents the by Dr. M. OKADA\ chrysanthemum varieties initiation of flower buds or its development. in Japan can be classified basing on the dif­ Cutting and planting should be done one ference in their responses to temperatui·e and month later than that of the autumn flowering photoperiod for flower initiation and its de­ varieties. Otherwise, they will often produce velopment. The results are fo1·mulated as crown buds or flower of poor quality on aged shown in Table 1. plants. The flowering time is from December to the beginning of February. c) Cultivation of summer flowering varie­ Year-round cut flower production ties under structures. Chrysanthemums are propagated by cutting Suckers from the plants which are pro­ or by using suckers which break from the pagated by cutting from the end of August base of stem or stool. The rooted young plants to the end of September are planted in bed should be planted in bed and be grown under under structures from December to January, inhibiting condition of flowering to keep After planting, temperature must be kept low vegetative growth by the time they will be not to initiate flower buds by the time they able to produce enough number of leaves on grow enough to produce satisfactory cut a long stem which is required as good quality flower in length. In general, when they ex­ cut flowers. The inhibiting condition for pand to 10 leaves and reach to 20-30 cm in flowering is different with varieties as is men­ length, temperature should be raised to 15,.., tioned above. 20°C to promote flower initiation and its 1)' Year-round production without regulation development. Flowering time is from the end of photoperiod of February to May. * OKADA, Masatsugu; Studies on Flower Bud Differentiation and Flowering in Cln·ysanthemum. Memo1·ies of the Faculty of Agriculture, Tokyo University of Education. Vol. 9, 63-202, 1963. -24- d) Cultivation of autumn flowering varie­ Cutting should be done in the middle of ties under structures. April. After one month, they are planted in Suckers are planted from the end of Decem­ bed. Time of flower initiation is the end of ber to the beginning of January. Cold require­ June. ment of suckers for break dormancy is much h. Cultivation of September flowering larger in general than that of the summer varieties. flowering varieties. Therefore, much attention The responses to photoperiod and tempera­ should be paid whether the cold requirement ture for flower bud initiation is the same as of suckers is satisfied or not by the time of the August flowering varieties. However, planting under structures. Suckers produced short-day is required for the development of in highland where the temperature by the flower buds. Planted at the same time as the end of autumn is low enough to break dor­ August flowering varieties, they initiate flower mancy are used for early planting for early buds under long day and keep standstill or flowering. turn to crown buds. Cutting should be done in As minimum temperature for flower initia­ the middle of May, one month after the time tion is higher than that of the summer varie­ of the August flowering varieties. ties, temperature can be kept higher to keep 2) Production of autumn flowering varieties vegetative growth, and should be kept higher with regulation of photoperiod than 15°C after they reach enough height to Both flower initiation and its development produce satisfactory cut flower in length. of the autumn flowering varieties can be With the exception of the above mentioned regulated by controlling of photoperiocl. Un­ points, the method of cultivation is not dif­ der long-day condition above 13.5 hours from ferent from that of the summer flowering May to August they continue vegetative varieties. growth, while under short-day condition under e) Cultivation of Okayamaheiwa type. 13.5 hours from September to April they can The responses to photoperiod and tempera­ flower provided the temperature is satisfac­ ture before flower bud initiation is almost the tory. same as the autumn flowering varieties. How­ a) Production from the middle of May to ever, the development of flower buds can the beginning of July by shading under progress under any day length. Therefore, structures without heating. they can flower without shading after the end Suckers are planted during winter months of May or under long day whenever they al­ under structures without heating. Shading Teady initiate flower buds. must be done every day after the end of April f) Cultivation of summer flowering varie­ to keep short-day condition of 10-11 hours. ties in the open. Materials of shading are black plastic film or From the end of Septmber to the beginning cloth to keep dark inside. of October stock plants are divided into a stool b) Production from July to the beginning with a few suckers, and they are planted in of October by shading. bed. The flowering time is from the end of One hundred thirty to 150 days are required :May to July according to varieties. from cutting to flowering. Thirty days are g) Cultivation of August flowering varie­ from cutting to planting, and 50 days are ties. from pinching a week after planting to start­ Though they are day neutral as well as ing date of shading. Duration of shading is summer flowering varieties, the required tem­ from 45 to 60 days depending upon varieties. perature for flower bud initiation is above High temperature inside the shade has an 15°C. This is the reason why their flowering injurious effect on the flower quality. There­ time is later than that of the summer flower­ fore this type of cultivation is prevalent in ing varieties.