Do Black-Eyed Susans Spread Easily? (What You Need To Know)

Black-eyed Susans, also known as rudbeckia, are enchanting yellow daisy-like flowers with a deep brown center that inspired their name.

The size black-eyed Susans can reach is equally as impressive as their color. Easily topping 2-3 feet tall, these flowers can add tall drama to borders or form large sweeps in a flower bed. In addition to being very tall, each plant can spread up to 18 inches across. Additionally, the plants will continue to spread each year once flowering has finished.

Black-eyed Susan produces large plants that spread easily during and after the growing season. Each plant can spread up to 18 inches across during the season. After flowering, their rhizome root system or self-sown seeds will help the plant spread further and establish itself in the garden bed.

Whether this spreading habit is good depends on what you want from your black-eyed Susans. I’ll include a few tips in case you want to encourage your flowers to spread or what to do if you prefer to keep the plants in a certain area of your garden. 

How do black-eyed Susans spread?

Black-eyed Susans spread via two methods: underground rhizomes (similar to a tuber) and seeds. Both forms of propagation will result in black-eyed Susans that survive and spread from year to year. 

Rhizomes

Rhizomes are very clever systems designed to help a plant spread from season to season without starting over from scratch each year. The rhizomes send out new shoots and roots from nodes that form underground and, aside from in freezing climates, will come back bigger and bushier year after year. 

Seed

In addition to these unique roots, black-eyed Susan flowers also produce more seeds than you’ll know what to do with. The brown center comprises hundreds of tiny florets, each of which will become a seed after pollination by bees, butterflies, or other pollinators. You can spread the seeds yourself or leave the seedheads on the plants, and nature will take care of it for you. 

In freezing climates, the plant may die back during the winter, but the seeds can survive even in freezing temperatures. 

How quickly do black-eyed Susans spread?

Black-eyed Susan plants spread relatively quickly, going from seed to bloom in approximately 100 days. As the season continues, the plants will continue to mature and spread until you have a plant base 12-18 inches wide. 

After flowering, the plant will get to work underground, sending new shoots and roots from its rhizome root system. 

One of the ways you can help your black-eyed Susans to spread is by scattering their old seed heads in your garden. As the seed heads mature, you can snip them off and sprinkle them in a place you would like to see more of the cheery blooms.

You can also collect the seeds for sowing in future years or at different locations. Snip the dried seed heads off the stems and store them in a jar or paper envelope. When you’re ready to sow the seeds, crumble the seed head in your fingers over their new site, scuff the soil over the seeds, and you’ll have a new patch of black-eyed Susans before you know it.

How to care for black-eyed Susans that are growing too big

It’s beneficial to divide your black-eyed Susans every 3-4 years to keep them healthy, promote new growth, and provide more room for the roots to spread. 

It’s a simple process, best completed in the spring or fall. 

1. Cut back the stems to ground level and trim the foliage to about six inches. 
2. Dig around your plant, loosening the soil.
3. Lift the root and rhizome of your plant in one clump.
4. Remove loose dirt from the rhizome by shaking it gently or washing it with a garden hose.
5. Separate the clump into pieces with a few healthy-looking shoots by pulling them apart with your hands.
6. Replant the divided roots to their new location immediately to prevent them from drying out. 

Should I remove my black eyed Susans after flowering?

You have a couple of different options for how to treat your flowers after they’ve finished bloom. Both options are easy to implement; it just depends on what your goals are.

Leaving black-eyed Susans in place

If you are happy with your black-eyed Susans and would like an even more impressive display next year, you can leave them where they are.

Black-eyed Susans are eager to please, so will spend the time between flowering seasons spreading out underground. Their roots will spread, and each new season, your clump of flowers will be a bit wider.

If you are happy with a blanket of these stunning yellow blooms, by all means, leave them in place. If you don’t want a massive display of their bright flowers the following year, you will need to remove the whole plant once flowering has finished in early fall.

Removing plants after flowering

To prevent your black-eyed Susans from spreading, you will need to remove the whole plant by cutting the flower stems and digging up the root system.

The rhizome will need to be removed entirely. Even a small part left behind will try to find new places to send its roots and shoots.

To remove your rhizome, first cut off the flower stems. Next, you will need to dig up the roots using a spade or trowel. Finally, gently brush away the earth until you find the rhizome (it will look a little like a piece of root ginger). When you have found the rhizome, gently lift it from the earth, being sure not to leave any parts behind.

Don’t forget to prevent the flowers from turning to seed heads if you want to completely avoid any new black-eyed Susan plants from sprouting in a particular area.

Are black-eyed Susans considered invasive?

Although they are efficient spreaders, black-eyed Susans are not considered an invasive species. After four years or so, the plants will slow their spread as their root system becomes tangled and matted, and the plant will more or less stay in its current location.  

That doesn’t mean the flower won’t continue to self-sow by dropping seeds each fall, so if you don’t want that spread, be sure to remove old flowers as they convert from flowers to seed heads.

Learn more about black-eyed Susans

If you’re new to growing these beauties, here are a few more resources to help you start on the right foot:

• Black Eyed Susan: A Complete Guide To Growing
• Black Eyed Susan: First Year Blooms & Other Flowering Questions
• What’s Wrong With Your Black-Eyed Susans? (Keep Your Plant Healthy)