The majority of daylilies bloom best in full light. They can tolerate partial shade but need at least six hours of direct sunlight every day. Because dark colors absorb heat and do not survive the sun as well as lighter hues, many red and purple cultivars benefit from partial shade during the warmest portion of the day. Yellow varieties are less sensitive to light levels and will usually produce flowers even when exposed to full sun all day long.
Daylilies are very hardy plants that can be divided every three years or so to keep them under control and to distribute their seeds more evenly. This division is easy if you take care not to break off too much root; just slice the bulb in half and replant the pieces about one foot apart.
You can also grow daylilies from seed. Let the pods ripen until they turn brown and drop into the soil where they will germinate within weeks. The seedlings will reach for the sky when they come up through the soil and because they are grown in full sunlight they will be ready to move once the last frost has passed.
Most part-sun to full-sun plants will bloom more profusely in full sun and produce fewer blooms in part sun. When a plant is described as part shade to shade, it prefers to grow in fewer than six hours of direct sunshine each day, with the majority of that time spent in the less strong morning sun. Plants require several hours of sunlight daily for healthy growth and development.
If you move plants from full sun to part sun, they will stop producing flowers until the amount of sunlight they receive increases. If you move them too early, before all their leaves have developed, they will likely fail to recover and will not be able to go back into flower when the weather becomes warmer. It's best to wait until all the plants' leaves are growing vigorously before moving them to part sun.
Even if you protect part-sunned plants with a large tree or building over the course of several years, most will still only produce white or pale pink flowers. These plants are typically called "shade flowers" or "filtered light flowers." Some species, such as Impatiens impatus, may produce red flowers in part sun but not in full sun. Other species, such as Ipomoea batatas (morning glory), may produce yellow flowers in part sun but not in full sun.
It's important to remember that although flowers appear earlier in part sun, this doesn't mean they'll always be available to pollinate.
The duration of the dark phase is critical. If daylengths exceed 12 hours, you can also encourage bloom in long-day plants like lilies, roses, petunias, and spinach. Day-neutral plants include sunflowers (Helianthus annuus) and tomatoes. These plants will try to bloom as soon as the soil receives sunlight, which can be at any time of year if the temperatures reach the required level.
If you want to grow flowers that don't need a dark period, select plants that are day-neutral or long-day. Day-neutral plants will try to bloom regardless of the length of the day while long-day plants require at least 12 hours of darkness before they will bloom. Roses are an example of a long-day plant while lilies are day-neutral.
Some plants, such as coleus, have both short-day and long-day varieties. These plants will not bloom unless they receive at least 6 hours of continuous darkness during their dormant season.
Short days affect some plants more than others. Summer flowers such as zinnias, cosmos, and marigolds are short-day plants that don't need a dark period to grow and reproduce. In contrast, winter flowers such as hyacinths and tulips are long-day plants that require a minimum of 12 hours of darkness to stop growing and go into dormancy for the cold season.