Yellow leaves? Did they go through a period of rest? If it's cool and they aren't getting optimal water and light, it could indicate that they are going dormant.
Yellow leaves tend to indicate low light. What direction does your window face?

My bulbs get down to 45 in the greenhouse. They are nice and green.

A photo would help.

Kristi

I have actually rarely ever had my bulbs go through a period of rest. Once in a while one will but most do not and I do not force them. When I see some more leaves yellow I will take a picture but I keep them fairly clean and when one starts to wilt and yellow I trim them off. The ones lately have been more than the average older outer leaves yellowing. It is a fair assessment that the ones yellowing are going dormant and I had not considered that.

They are in a full Southern window partially for light and partially for warmth.

Then you grow them as evergreens, which many on the list do. Are you providing adequate fertilizer? If they aren't going dormant, the yellow leaves mean a lack of something. It sounds like this isn't the case of just the occasional leaf dying.
K

I would like to think I am fertilizing them enough. I fertilize every time I water them but I do grow my differently. I do not think it is a fertilizer issue given the fact that it is one group in particular and others are still flourishing. The other unusual factor is that the two group I am comparing are from the same batch of seed. One set is far beyond the other and does not seem to be catching up.

I do expect there to be a difference between the two groups because I was experimenting with growing methods but I did not expect the one group to begin yellowing and remain stunted after transitioning over to the method I found most successful.

Well, they are unhappy about something. Maybe they will all lose their leaves and after a short rest, start growing again. Sometimes these things are a mystery!

Could be any of the following:
Light, temperature, water, fertilizer. If everything is the same then there is no reason that one set is acting odd. Perhaps you just need to have a stern talk to them!
:-)

I've got a closely related problem, but I don't want to open a new thread.

I have been forcing my bulbs for the last couple of years. Usually they were still in relative good shape at the end of the year, so around November/December I started to give less water and moved them into the cool basement around Christmas time.

This year I started earlier with some, around September and had them in the cellar for the whole October to have them flowering for Christmas.

Something went not as planned ... I think they were mostly ready for the dormancy period, the leaves were going leathery, the outer leaves getting yellow tips.
I moved them back into the flat and put them on our north-facing window which I descibed before. Although they don't get direct sun, it's quite bright and they thrived there in the last growing season. Now they don't want to grow.
I think the problem is that I widened the windowsill with a huge board, 120 x 40 cm (47 x 16 inch) which is good because the big pots won't fit on the other windowsills but I think it keeps the warmth of the radiators from the pots. Temperatures go down to around 14°C (57°F) at night and maybe lower since the windows are somewhat leaking (?)
The plants on the other windows in the warmer room directly shot scapes and leaves upwards, but the "colder" plants were less enthusiasticly growing. Sydney showed it's scapes rather soon but they are staying in the bulb neck for 2 months now. Just now they are moving again, I put the pots on the floor during nighttime, so that they don't get too cold.
I think I should have left my Amuptos grow, but I wanted them all to be ready at the same time, I repotted all my plants when they came out of the basement - but they don't show the slightest sign of growth. I feel really stupid.

Do you think it's the temperatures during night (during day it's around 19°C [66°F])? Sadly I have no alternative space for these pots!

This post was edited by betonklotz on Thu, Jan 8, 15 at 13:30

I wanted to bump this thread up again since my Amputos are still dormant. Any suggestions?

I think H. Amputo may be a finicky hybrid that doesn't perform as expected. Give it a little time. As long as the bulbs feel firm and you still have roots things are probably fine.
K

Hello BetonKlotz, cold windowsills do not work well for me, when it comes to forcing during winter. 14 to 19°Celsius is too low. The minimum temperature (of the substrate!) should be 20°C, and up to 25°C are even far better. Did you already consider the installation of electric heat mats?

Hans-Werner,

I thought about heating mats too and I will definitely try those next growing season.

Kristi,
Sadly I watered my Sydney once in this dormancy and the substrate was still wetter than I expected. They where well anchored in the new cocofirbre when I repotted them. Now, I think the roots are molding away. I should have left them in a darker but warmer spot without any water.