Callistephus is a genus of only one species from sub-tropical China and Japan They prefer warm growing conditions so should be be sown quite late in Spring or when night temperatures are increasing. Cold nights are not to their liking. They are easy,fast growing Summer and Autumn flowering annuals which enjoy heat and deep watering. China asters come in a bewildering array of forms and colours. All are very easy to grow appreciating a liberal dressing of lime and complete fertilizer at planting.
Once temperatures have reached their preferrred range ( think Tomatoes) they grow quickly, given full sun and reasonable moisture, providing a long lived show of vibrant colour until frost cuts them down.
Seeds should be sown in seed trays or plugs in a warm position. The young plants should then be transplanted into their flowering positions in Early Summer or when all fear of frost has past. Low temperatures are not to their liking and nothing is to be gained from trying to plant them out too early.( think Cucumbers)
The bed in which they are to be planted should have been dug over a few weeks prior to planting to allow for a crop of weeds to germinate. Once these interlopers have been hoed off and left for a few days to whither one hand-full of complete fertizer should be spread over each square metre of soil and lightly forked in.
Planting can then proceed. If the weather is hot small branches should be used to shade the young seedlings until signs of new growth become obvious. Liquid feeding for the first six weeks makes for sturdy plants as does nipping out the leading bud to encourage branching.
Once the young plants have more or less filled their positions but whist there is still some room between them it is a good idea to thrust leafless twigs of various sizes into the ground between them so that the gruop becomes a self supporting unit. Late summer storms can cause havoc with annual bedding laying watse to a good deal of planning and effort.