How to help annual plants to go through the winter: some main points
Do not forget to observe soil and plants for insects both on top and underneath the leaves. If you notice any pests, spray with Soap-Shield. Take the plant out of the pot and check the soil for any signs of slugs. If slugs are present, you d better to wash off all the soil and transplant your plant using fresh potting mix.
Choose only healthy plants to bring indoors or take cuttings from them.
Before bringing the whole plant inside, cut it moderately.
Water the plant carefully. Excessive watering is the main course of destruction of plants grown indoors during the winter. Use the finger test: press your finger into the soil and if the soil feels dry it is time to water.
Humidity levels are low in most houses during the winter, and this can encourage spider mites. Hold the plants damp or place them on a tray filled with water. This will help to create humidity around the plant.
Do not over fertilize, because plants need less food during the winter: their growth rate is slower and they need some rest.
Place the plants in an area where they can receive the maximum amount of light. You may need to add an artificial light source. Fluorescent ones do a great job.