Dear Karimatul,

First you have to develop the stages of plant development of the china aster. Please, see about Stevia rebaudiana attached to my page. Next, you have to develop an experiment harvesting the plants under different stages and analyse the responses. Harvesting flowers as the commercial product is different from harvesting seeds for high quality. Pay attention to the spacing in-between and within the rows because there will be a series of modification in the plant architecture. Pay attention in the flower anthesis. It occurs from the outside into inside the torus. As cut flowers, the harvest moment needs to have some flowers under anthesis; two or three flowers in every Fibonacci design to arouse interest of all the costumer and have the other ones open in the costumer home for supplying their satisfaction with the product. As seeds, the harvesting is when the achene is mature and dry. The number of flowers in the Fibonacci line can be stages of maturation. Look the sunflower torus under maturation. The torus is large and visible for beginners. In my page of Researchgate, there is a paper about germination of Aster seeds.

I hope you enjoy these suggestions.

José Walter P. Carneiro.

You will find a lot of literature regarding this topic. You should harvest seeds at different times and then go for a comparison to know the best time for seed quality. We have seen that in Hyptis and Basilicum there is a lot  of spatial and temporal difference in seed size and quality  - you can actually design very elegant physiological experiments for this.

I you harvest seeds before natural shedding, you should realise that they have not achieved full vigour. This can be partly compensated by drying the seeds slowly, enabling enough moisture in the seeds to finalise the building-up of protection mechanisms. Look for literature on seed maturation and chlorophyll fluorescence sorting to see the effect of a too early harvest on seed vigour.

Probably you are asking for a crop which has indeterminate growth habit. If it is the case, you can harvest the seeds which are matured having less than 20% moisture. Like mungbean, you can harvest the brown or black colored pods but the plant will still have the flowering going on and the green immature pods on the plant.