i have lots of lobelia in the garden. how come some of it has really died off and the rest is still flowering? they all get enough sun and water and they are all the same type of lobelia.
It could be that some plants have gone to seed or maybe wind damage, if you mean the type of Lobelia that is used in hanging baskets etc it is an annual plant and will all die as the weather gets colder.
It could well be that the original plants have self seeded and the younger plants are now into their 'prime', given the weather. They will all die off in due course and need replanting in the spring as Lobelia is an annual. (only lives one season).