They will survive in really tough conditions but that does not mean they will flower well or even grow well. Survive does not mean thrive.
To get the most from your daylilies give them the growing conditions they prefer and you will be rewarded with beautiful blooms and healthy foliage.
Daylilies are sun lovers. They want at least six hours of direct sun a day. They will tolerate part shade but they will not flower as well and the foliage will not be as lush. The bloom scapes will also lean toward the sun. The lightest coloured daylilies, like the near whites and pastels, need sun to bring out their colouring and to show off the diamond dusting or sparkle that is present on many of these blooms. Dark coloured daylilies, like the deep reds and purples, will maintain their colour intensity better if they can be situated where they will receive a little shade over the hottest part of the day.
Like most perennials, daylilies prefer rich, well drained soil that has good aeration. They are tolerant of a wide PH range but prefer neutral to slightly acid soil. They are very heavy feeders and will grow best with lots of organic material incorporated into the soil. We mix well rotted horse manure or leaf mold into the beds when we build them and use a mulch which will add additional organic material as it decomposes. This soil drains freely and has lots of available nutrients for the plants. We do not use chemical fertilizers, preferring to depend on building fertility in our soil. If your soil is too sandy or is heavy clay add compost to make it more daylily friendly. High quality daylilies will perform in most soil conditions but to get the best growth and bloom build up the quality of your soil. It's worth it!
Daylilies, like most perennials need well drained soil. They dislike winter wet and could rot if planted in low lying areas that remain soggy over long periods of time. Occasionally we have experienced flooding in the bottom part of our daylily field as a result of spring snow melt. We have had plants under water for a brief period of time and they have survived but exposure to longer periods of wet can cause the crowns of the plants to rot.
Daylilies do not have an aggressive root system and will not grow well if they have to compete for moisture and nutrients with trees and other moisture grabbing plants. Cedar hedges are especially problematic because the roots will quickly overrun the daylilies. If the plants have to survive a lot of root competition water them more and be prepared to dig them up and reset them if they become over run with tree roots.
Potted daylilies can be planted at any time of the year. Late season plantings should be mulched to prevent frost heave which will expose the roots of the new plants and damage or kill them. Bare root daylilies can be planted any time up to the middle of September but planting by the middle of August is preferable to allow the plants to establish a good root system before the winter.
Daylilies love water, especially in the spring when they are actively growing and setting buds for that year's flowers. If we have a wet spring we can guarantee that we will have a spectacular crop of blooms. To flower well they need a deep soaking once a week. Give the soil a chance to drain before you water again. A mulch will help to conserve moisture, suppress weeds and keep the leaves clean.
Around the middle of September we cut all our daylilies down to a height of 15 to 20cms. We pick up all the old foliage and compost it. At that time we top up the mulch to protect the plants for the winter.
Daylilies spread by sending up new fans from the edge of the clump. Over four or five years the clump can become very dense and the flowers will be fewer and smaller. That is when you know it is time to divide the plant. To do this we did up the entire clump and wash it off so we can see what we are doing. We cut back the foliage to about 30 cms to reduce stress on the plant and make it easier to handle. Working from the top we split it using a sturdy knife. The new divisions are planted at the same depth they were growing. They will rapidly produce new roots and new top growth. The best time to do this is just after flowering. That gives the plant time to settle in before the winter. You can also divide in the spring but it will affect the bloom that summer.