I have a smallish bed of tulips, about 3x10 or so. I planted a mix of colors 5 or 6 years ago and they've been doing really well...after I learned to put bird netting over them to keep the woods rats from eating them.

I've noticed the last couple of years that the seem to be migrating towards all one color. There used to be a vibrant red, bright yellow and pink with white edging. It looks like this year they're pretty much all going to be a pale pink.

Is that a cross-pollination issue? Maybe a health issue? I leave the greenery until it dies off before I remove it. I read that excessive water and/or fertilizer during their dormant period is bad for them, but I don't think that's the issue.

I usually plant Nasturtiums in that bed for Summer/Fall color. No fertilizer (Gene Wilder said "Always be nasty to Nasturtiums" in the movie Silver Streak...) and no extra water unless we have an extended dry period.