First, the lychnis plants are reseeding, short lived perennials that are often treated like annuals. I wait for mine to flower and drop some  seeds and then I uproot the entire plant as soon as it starts to decay and look ugly. Next year the new seedlings take over. I have tried cutting them back to get more blooms but no luck in my garden. As for hydrangeas, you need to make the soil less acid to get pink blooms. This means adding dolomite lime around the base of the shrub now and again in early spring next year. It may take a few years to change your soil acidity and see results. It may be more practical to by pink blooming hydrangeas. Hydrangea  Invincibel Spirit is an example of a hydrangea that will bloom pink no matter what type of soil you have. Keep growing, Marianne Binetti