* Deadhead. To keep flowers blooming, it's important to promptly cut off dead and dying blooms, not just to keep the garden tidy but to prevent the plants from making seed. Setting seed tells a plant that the workday is almost over--that's there's no need to grind out a few more flowers--and the plant can shut down for the season.
This is especially important with some perennials, such as alstroemeria. The whole flower stalk in this case should be sharply yanked from the roots. This will encourage the formation of more flowering stalks. Cut back delphinium stalks so only two or three leaves remain at the stalk's base, and the plants will bloom again in late summer.