In my garden I preserve some "wild" tulips. I say "wild" because they were planted many years ago by some ancestor of mine, I believe around late 1700-beginning of 1800. They are of a quite raw quality, not as beautiful as modern hybrids. They have long leaves, very thin, like if they were made of paper, red flowers with cuspid-like petals, and they flower very early, about 1 month before the other tulips.
Here's a picture of them: http://www.panoramio.com/photo/105948977
During time, they spread around all the garden. The point is that I notice that many of them are much smaller then usual and do NOT flower.
Is it a genetical issue (in what they have never been mixed)? Or just a question of exposure to the sun, soil, of some other kind of environmental condition (bulbs are very very deep in the ground, maybe more then 1 m: think that in the same place, my granmother used to work the ground to plant tomatoes, but bulbs were deeper!)? Or perhaps they just belong to joung generations?
In any case, is there a way to make them flower?
I already checked many questions, such as Should I keep tulip bulbs that didn't flower this year, or replace them with new? , but they seem not to exactly address my problem.