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The following articles should be of some help to you: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm
https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/tips-for-pruning-hibiscus-plants-when-to-prune-hibiscus.htm

This article may help:
https://www.gardeningknowhow.com/plant-problems/pests/insects/prevent-caterpillars.htm

http://hibiscus-sinensis.com/care.html

Try this link.

They only bloom for a day, sadly.

It could be a lack of nutrients in the soil, or that the plant is getting more sun than it did last year. Both of these can influence the vividness of color on the flower. It may also be that the original plant was grafted and the scion (the part you saw last year) died and was replaced by the rootstock which produces a different color.

There are many species of hibiscus. The overall majority are best propagated through cuttings. However, hardy hibiscus can be divided and is usually done so in spring. It can be divided by cutting the plant in half. Stick a shovel in the middle of the plant between the stalks and cut straight down into the root ball. Then dig out from around the plant (about a foot around). Pop them up out of the ground and then replant.

Here is an article you may find helpful: https://www.gardeningknowhow.com/garden-how-to/propagation/propgen/dividing-plants.htm