While technically an annual and not a true geranium, you can grow Martha Washington geraniums indoors and encourage them to bloom for several years. Repeating the blooming process for these plants is an ongoing process.
- Trim back growth
Once the flowers are spent, trim the geranium severely. Cut the stems so only 4 inches remain.
- Repot the plant
These plants do best when slightly root bound, so it is acceptable to repot using the same pot. However, they do require fresh potting soil for the best chances at blooming again next season.
- Begin the rest period
Flowering takes a lot of energy from annuals, and they need rest before you begin encouraging them to form buds. Since they do not form buds unless the night temperature drops to between 50 or 60 degrees, let them rest during the warmest months of the year by moving them to an area with indirect light. Stop feeding the plant and water sparingly during the rest period.
- Cool the plant to set the buds
Once the night temperatures drop to 50 degrees, move the plant outdoors in the evening to set the buds. Protect it from frost. Resume a normal watering and feeding schedule. Once the flower blooms and the blossoms are spent, begin the process again.