So, what this means in practical growing sense, is that the best time to grown coriander is in the cooler seasons. I plant my coriander in early spring (August/September) and in late summer (February, March). Coriander plants do not like being transplanted (stresses the plant) and l also find it difficult to grow coriander in pots because if you forget to water the plant, then the plant gets stressed. Stress is a signal to plants to start to produce seeds as quickly as they can.
If you do want to have lots of coriander leaf during the warmer months, then it is best to plant the coriander in the coolest spot you have and if you are incredibly organised (and who really is this organised), plant fresh seed every couple of weeks.
If you have the space, then letting your coriander flower and go to seed is amazing. Coriander flowers taste divine! They are a little burst of intense coriander goodness. Once the seed head turns brown, then you can harvest them and put them in a warm place to completely dry off and they you will have your own coriander seed to grind up and use. An added benefit of letting your coriander go to seed, is that they will spread their seeds through your garden. It always amazes me how these seeds will grow so much more easily in places of their choosing that where we want to sow them! This winter, I had so much coriander growing on my paths and outside my drying shed from where I dropped the seed after harvesting it – I have harvested this coriander for months now. The photo is of one of the coriander plants which is growing on bark placed on top of weed cloth!