Black-eyed Susan, or rudbeckia, is one of the most cheerful yellow blooms to grow. When may other summer perennials fade, it continues to put on a display into fall. But, by mid-September your Black-eyed Susans may be starting to look a little tired and worse for wear – that's when it's time to give them a bit of attention.
Black-eyed Susans are hardy perennials across USDA zones 3-9, but require some post-summer care to prepare for frosts and make it through winter unscathed. Now is a good time to collect seeds and sow them for brand new plants, though you also want to ensure you leave some seedheads for wildlife to enjoy. Likewise, you can divide your rudbeckia now to reinvigorate your plants and grow more elsewhere in the garden.
Ultimately, what to do with black-eyed Susans in September is all to do with a bit of tidy up at the end of its flowering season to ensure it comes back better and stronger next year. So, with your Felco F2 pruning shears from Lowe's in one hand, here's what the garden experts recommend.
1. Collect Seeds
September is a good time to start harvesting black-eyed Susan seeds if the flowers have produced seedheads. You may find it has a few remaining flowers, in which case you may want to wait until October to collect seeds.
'You want to wait until the petals have fallen off and the central cone is brown, crispy, and completely dry,' says Lindsey Chastain, homesteader and founder at The Waddle and Cluck. This indicates the seeds have ripened.
'Cut off the heads and place them in a brown paper bag to allow them to keep drying,' Lindsey continues.
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'Once dry, you can use your hands to shake the heads and loosen the seeds. Store them somewhere dry and cool. I usually just keep mine on a shelf in the garage,' Lindsey explains.
To store seeds correctly, use a sealed seed envelope (you can pick up DIY ones from Walmart) or seed tin (like this green one rom Amazon). This will keep moisture out and ensure the seeds stay viable for planting.
Lindsey Chastain, a dedicated homesteader and skilled writer, is the driving force behind The Waddle and Cluck, a platform that celebrates sustainable living, gardening, and responsible farming
2. Leave Some Seedheads for Wildlife
The best plants for seedheads not only bring architectural value to the fall and winter landscape, they also help feed birds in winter (as well as other wildlife, like squirrels) where other natural food sources are scarce.
For this reason, Lindsey recommends leaving some seedheads for wildlife to enjoy.
'After the seedheads completely dry out, the seeds tend to fall to the ground. The birds, squirrels, and chipmunks will come and eat them, which gives them food later in the season,' she explains.
In particular, American Goldfinches and House Finches are the primary birds that eat black-eyed Susan seeds.
Growing other native plants that feed birds in winter also provides a food source for wildlife. This includes chokeberry (which you can find at Trees.com, formerly Fast Growing Trees) and coneflowers (you can find coneflower seeds at Botanical Interests).
3. Sow New Seeds
If you're wondering when to plant black-eyed Susan seeds, September is a great time to directly sow the seeds outdoors.
You can use the seeds you harvested or pick up rudbeckia seeds from True Leaf Market, and use your seed sowing kit to start growing a brand new plant from scratch.
'You can go ahead and sow them outdoors this month because fall and winter provides the cold stratification they need to germinate,' Lindsey explains.
If sowing in fall, it's best to do so on prepared ground with a well-draining, nutrient rich compost. Thinly scatter the seeds on the surface and don't bury them. Rudbeckia seeds need light to germinate. Do this before frost, when the ground is still workable.
Alternatively, you can sow seeds indoors in late winter or early spring, harden off seedlings after the risk of frost has passed, and transplant them.
This seed sowing tray from Amazon makes transplanting easy, thanks to the integrated lifting handle to remove the seedlings without disturbing roots.
4. Remove Any Diseased Plants
One of the things to clear from the yard in September before frost is diseased plants to prevent spreading. For Lindsey, black-eyed Susan is one of the most important to check.
'My black-eyed Susans are chaos gardened among other blooms, so at the end of the flowering season I always go through and remove anything diseased and dead,' Lindsey describes.
Doing so will protect your planting from overwintering diseases like powdery mildew, ensuring next year's display comes back strong and healthy.
You can use various tools to remove such plants, including this transplanting trowel from Amazon.
Anything that is dead but not diseased can be placed in your compost bin. However, there isn't a need to cut back black-eyed Susan until early spring if you would like to leave seedheads for wildlife and winter interest.
5. Divide Plants
'You can divide black-eyed Susans either as they enter dormancy in the fall or as they emerge from it in the spring,' says Nastya Vasylchyshyna, plant expert at Botan App.
'Divide them every few years, depending on their growth rate. To do this, simply dig up the plant, preferably digging a little away from the stems to preserve as many roots as possible. Then, use the edge of a shovel to divide it into 2-4 sections, depending on the size of the clump, and replant them in new locations,' she advises.
Dividing perennials like this every few years helps keep plants productive and reduces overcrowding. As Nastya notes, you can use a shovel or you can pick up a hori hori knife from Amazon for a more specialist tool to make clean cuts when dividing plants.
When you have replanted the new clumps of your rudbeckia, ensure to water well to help the roots settle and establish.
Anastasiia Vasylchyshyna is a biologist and botanist with 5+ years of experience in the plant care app industry, writing on plant care and plant pathology – from seasonal plant guides to diagnosing houseplant problems. She holds a biology degree from Taras Shevchenko National University of Kyiv and specializes in turning scientific knowledge into practical, actionable advice.
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As we move later into fall, it will be important to winterize black-eyed Susans to ensure they survive the coldest conditions and re-emerge in spring with growth. This includes mulching around the base of the plant to provide insulation for plant roots. Luckily, there are plenty of free fall mulching materials you can gather from your yard.
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