Cross-pollination

Chilli flowers are self-fertile, and most pods set from their own pollen without any help. But the flowers are open and insects visit them, so pollen does move between plants wherever compatible varieties flower near each other.

It does not change this year's pods

This is the part that catches people out. A superhot growing next to a sweet pepper will not make the peppers hot. The pod is tissue of the mother plant and carries the mother's characteristics, whatever pollen happened to fertilise the flower.

The cross is in the seeds. Sow them the following year and the consequences arrive: plants that take after either parent, or land somewhere between the two. A pod can look flawless for its variety and still be full of crossed seed.

Reducing crosses

In rough order of reliability:

• Grow one variety. Complete isolation, no effort, rarely practical.
• Bag the flowers. Cover selected trusses with fine mesh or organza before the buds open, and tag them so you know which pods to save from. This is essentially what commercial isolated seed means.
• Distance. It helps, but pollinators travel a great deal further than most gardens are wide. A few metres between pots is not isolation.

Species matters here too. Capsicum pubescens crosses with the other four only rarely, and the hybrids that do form are usually sterile. Annuum, chinense and frutescens cross readily.

If you are not saving seed, none of this applies. Grow whatever you like next to whatever you like.