Sea Holly Alpinum (Eryngium Alpinum Superbum) - Eryngium Alpinum Superbum is nothing short of fantastic and is easy to grow from Eryngium seeds. It is commonly known as Alpine Sea Holly, and it is one of the showiest Sea Holly plants available on the market. The metallic stems and large thistle-like flowers mature to an intense steel blue color from summer through fall.
It’s a bit unconventional, but when I saw this big petunia plant thriving in a tree trunk it caught my eye. Horticulturally, this is not recommended practice for any tree you are trying to save, but it’s an interesting idea for utilizing an old stump. The simplest way to do this would be to simply buy a basket of petunias and transplant them in the opening