beckygardener said:..... much of the "older" foliage is turning yellow, then shriveling up and changing to brown. The older leaves are dying as the new ones grow in. Is this because they are coming out of Winter dormancy (including evergreens and semi-evergreens) and putting out new foliage?
Becky, there are several different patterns to how leaves age and die.
The yellowing and aging of leaves is called senescence. It is separate from dormancy.
When a fan sprouts (comes out of dormancy) a new leaf is produced every few days. We could think of the new leaves as being born one after the other. How many days there are in between each new leaf appearing and how quickly the leaves grow to be adult size or mature depends strongly on the temperature but also on other factors. Leaves have certain lifespans - they can stay alive for a certain number of days. How many days they stay alive will probably be different for different cultivars but is also strongly affected by temperature.
The leaves on your plants might be yellowing and dying because they have reached the end of their normal lives. This sort of aging can happen throughout the growing season. Each leaf would start to yellow and die when it has reached the end of its normal lifespan. The deaths of the leaves would be separated by approximately the same number of days that separated their "births".
Another pattern of aging is called top senescence. That is when all the leaves start to yellow and die at the same time. In many plant species this happens after the plant has flowered. This can also happen when the plant begins to go dormant. Or the plant can go dormant but the top (all the leaves above the ground) may not senesce until much later.
The leaves of a plant can also die at the same time when the plant has experienced a strong stress. Very low temperatures or very high temperatures, strong drought perhaps with the leaves wilting, too much fertilizer and so on may cause all the leaves to yellow and die.
Can daylily plants go dormant when they are not receiving enough fertilizer?
Yes, how much fertilizer the plants receive can change how daylilies grow. How much water they receive can also
probably change how they grow.
The best example I can give is 'Heavenly Harmony". It normally grows in my field without any added water or fertilizer (quasi-natural conditions). Growing in those conditions a scape appears in early June and it does not produce any new leaves after that until September. Its crop of leaves stays green until late August or early September. It is dormant from June to September. One autumn I fertilized it heavily with high nitrogen. The next spring as it started to grow I again fertilized it heavily with high nitrogen. That year its growth pattern changed. It produced new leaves all summer. 'Ophir' responds to high nitrogen fertilizer in much the same way. Its normal growth pattern when not fertilized or watered is to become dormant in July and stay dormant until the next year. Again its leaves stay green and they do not senesce until October or November. When it is heavily fertilized with high nitrogen it grows new leaves all summer and has even rebloomed.
