Last spring my newly planted Aliums towered above spring plants as single stems. I let them develop and keep their seed heads as they looked magnificent for the rest of the year. This year they have emerged as much shorter multi-headed stems. What have I done wrong?
They do that for me too. Maybe best to lift and pot up. It's what I will do after flowering
Multi headed as in more than one flower per stem or multi-heaed as in more than one stem?
Sorry a bit inprecise - I'm a Newbie you know!
The aliums have multi stems not multi-headed stems. I left them last year to form the seed heads and to give lift to the border - that's what all the gardening programmes seem to encourage you to do as they look "pretty during the winter".
Ok, not to worry. What has happened is that your single planted bulb has split and now you have 2 bulbs. The reason for their lack of height could be down to lack of food. The need feeding when the leaves first appear. Once the flower arrives the leaves have finished their bulb feeding duties and are dying down for their Summer rest. Leaving them to set seed may be pretty but it does take an awful lot out of the plant. So that is the answer, feed them next early winter and remove the spent flower heads.