The difference between Rudbeckia and black eyed susan is simple. Rudbeckia is the plant family name that covers about 25 species. Black eyed susan is the common name for just one of those species. Think of Rudbeckia as the last name and black eyed susan as the first name of one family member.
I got confused by this at a garden center a few years back. Three plants all had "Rudbeckia" on the tag but looked nothing alike. One had the classic gold daisy shape I expected. The second had smaller, stiffer flowers on upright stems. The third had droopy petals and stood over 5 feet tall. These were three distinct species in the same genus. That trip taught me to read past the family name and check the full species label.
The full range of Rudbeckia species covers plants from short wildflowers to tall giants. All 25 species are native to North America. They share the dark center cone with ray petals around it. But the size, shape, and growth habits change a lot from one species to the next. Some are annuals that die in one year. Others are true perennials that spread and live for a long time.
Experts at Maryland Extension count 4 varieties of black eyed susan. Each one grows in a different part of the country. But they all share hairy stems, rough leaves, and gold flowers with dark centers. Those are the traits most people picture when they hear the common name. The variety names don't matter much for home gardeners since they all grow the same way in your beds.
The Rudbeckia hirta vs Rudbeckia fulgida matchup matters most for home gardens. You see both at nurseries all the time. Hirta self-seeds and dies after a few years, giving you a wild meadow look. Fulgida spreads by roots and forms a clump that grows bigger each year. Pick Goldsturm for a tidy border that stays put. Pick hirta for a looser style that shifts around your beds over time.
You can figure out which one grows in your yard with a quick root check. Dig at the edge of a clump and look for thick roots that link the stems. If you find runners between plants, that's fulgida. If each plant stands alone with its own root ball, that's hirta. I did this test in my own garden and found both types growing 3 feet apart without knowing it.
Once you know which species you have, you can care for it the right way. Hirta needs you to let some flowers go to seed each fall so new plants fill the gaps when the old ones die. Fulgida needs you to divide the clump every few years so it stays healthy and blooms strong. You can also mix both species in the same bed for a display that self-renews and spreads at the same time. Match the right species to your goals and your Rudbeckia beds will give you years of gold blooms with very little fuss.
Read the full article: Black Eyed Susan Complete Growing Guide
