It can be either but in this case I would say over watering. It has been a very rainy spring. Your plug trays look wet but perhaps you just watered. Are they inside or out? The ones outside will be fine. Mine have seen drought and nonstop rain on various years and nothing fazes them once they are established. If you ease up watering the potted ones they will be fine too.

The first 2 pic is planted in the ground and what I don’t understand is why just that lily showing symptoms but not the other. The plugs are kept outside and they only get water when it rains otherwise it can get bone dry from the sun. If it stays dry for couple days then I would go water by hand. When I pulled out one of the plugs, the roots were all intact and white. Also I sowed the bulbils last summer and I left it in my unheated garage all winter and they finally germinated this year. It’s been very rainy but since the ones in the ground are new plantings and still unestablished shouldn’t it appreciate the excessive water more?

When it comes to watering lilies more is not better. Keep in mind that the bulb hold lots of water and releases it slowly as needed. Since they are about 4 in deep it takes a long time for that layer to dry out. You do not need to water often just because the surface looks dry. I know that's a hard habit to break but these are not treated like plants with shallow roots. I water my Asiatic lilies only every 8 or 9 days as needed. My surface soil looks like a desert but they love it. These have been blooming now for 2 weeks in hot southside Virginia where it has been 90° lately. Pics on comment.

Heruga, I thought tiger lilies were Lilium lancifolium, not Asiatics?

Yes they are Lilium lancifolium. I’m not sure whether they have the same watering requirements as other Asiatic lilies. But I do agree bulbs are more susceptible to rot and that these lilies can also tolerate drought. But I think tiger lilies are more tolerable of wetness though. We have gone through an excessively wet period from last July until current and all the others except this one in the pic is doing fine. I planted some 2 years ago for my grandma and they come back bigger and bigger.

I planted some bulbs this spring and they look beautiful. We've had a lot of rain too and everything is soggy. They are in a bed that used to have a rock mulch ( previous owner), so there are still too many rocks in that bed tho I'm trying to get rid of them. I think the lilies might be planted on top of a layer of rocks and that's why they look so good. I don't have a picture and it's too dark now. The buds are almost ready to open.

I would let all of them dry out. Try to keeo the plants you can out of the rain so they can dry out. Everything here has been soggy and nothing has time to dry out before the next downpour hits. A lot of my plants are stressed and turning yellow.

Heruga, this is my tiger lily.

I planted the yomogi in a pot so it doesn't take over. I want to overwinter it.
This is the ashitaba koidzumi. It's growing very slowly. It seems like an eternity!
I couldn't find any Patrinia scabiusifolia plants without selling my soul, so I'm trying to germinate seeds now even tho it's late. I planted a Valerian because it's the next best thing.
Some ferns and Japanese painted ferns.
My variegated Polygonatums didn't make berries. The native Solomon's seal is bloomning now. P. biflorum comutatum I think.
A rabbit ate the tip of my Apios vine and took off like a speeding bullet. And now, I just saw more bunnies! :(

Do you happen to know how many years it takes for a Lilium lancifolium bulbet to reach flowering size?

I was going to plant the Apios americana in the ground, but the rabbits forced me to change my plans lol.

Very nice Jay. Thanks for sharing. A bit disappointed the Solomon’s seal are sterile. Although I’m surprised your tiger lily is about to bloom this early in the season. Naturally they bloom in July to August. Especially in a colder area like yours where spring starts later. Was yours forced in a greenhouse? This is only my first time growing these lilies from bulbils so I am not sure but I assume it will take 3 years at the least.

Is that why the Solomon's seals didn't have berries, because they are sterile? My lillies weren't forced. I just bought the bulbs at Home Depot in the spring. We've been swamped with rain so all the plants are more ahead than they should be. Those variegated Polygonatums will spead fast by rhyzomes if you keep them well watered and fertilised. Did you get any Myosotis that flowered?

I think the lilies might be mislabeled. The foliage doesn’t look typical of that of L. Lancifolium and even with the rain they shouldn’t be blooming this early. We’ve had tons of rain too. We’ll see when it blooms I guess. I’m not 100% sure they are sterile since I cannot find any info regarding that but judging how none produce berries it probably is or only seldom produce berries. The myosotis seeds I grew in flats all died about 2 months ago. I don’t know why I always fail with small seeds that you mass sow with. Such as artemisia princeps as well. I do ok germinating bigger seeds but never any luck with tiny dust sized seeds. So I sowed the myosotis in the ground and covered it with a milk crate so nothing bothers it and so far it is doing very well. They are growing far better than the ones I started in flats, indoors in March.

That would be just my luck that I bought some cheap imitation of Lilium lancifolium. The one other time I tried growing them, voles ate all the bulbs. Would you be able to tell the difference? The deer just ate all my Rudbeckia down to the ground. They and the rabbits take different shifts lol.