Why doesn't my reed grass produce seed heads?

Asked July 30, 2015, 6:03 PM EDT

I have a several year old Karl Foerster feather reed grass that will not produce seed heads. The grass itself is big and lush. In another garden nearby, my pampas grass didn't produce seed heads either and died off after that year. I suspect the soil, but how can I adjust it?

St. Louis County Minnesota

3 Responses

The most likely reason you don't see blooms is too much shade. 'Karl Foerster' needs full sun and will only bloom sparsely in shade.

Another possibility is too much nitrogen. That would give lush green growth at the expense of flower and seed. Have you fertilized?

I do not think it is a soil issue. 'Karl Foerster' is very adaptable. I don't know what your pampas grass is - that's more of a generic term - so I can't say what the problem is there. But shade is often the problem when something doesn't bloom.

Thanks for your reply.
the grass is in full sun. I have not fertilized. What should I use to counteract too much nitrogen?

It would get too much nitrogen if it were excessively fertilized, such as perhaps in a lawn situation. Nitrogen is eventually diluted by rain and watering.

Other possibilities would be heavy clay soil (although KF is adaptable), standing water (again, KF is adaptable), or it is just late (although another master gardener from St. Louis County said hers was fine).

So I don't really know what is happening. I'd suggest waiting.

By the way, KF is hardy to zone 4, while some sections of St. Louis County are in zone 3 (depends on how close you are to the lake). So it may not be reliably hardy. That may have been what happened to your "pampas grass."