When to cut back black eyed Susans – the experts are split on the best time

Black eyed Susans are so-called for the plant’s dark central head and they can bloom for a long period of time through summer and fall. They are also commonly known as rudbeckia and come in a range of annual or perennial forms. 

If you are growing perennial types, then you will need to cut back black eyed Susans come the end of their blooming period. When growing rudbeckia you can either cut them back come fall or spring, depending on your preference.

No matter which option you choose, and it may depend on the style of your backyard, the process is thankfully a simple one. We take a look at the advantages and disadvantages of each to help you decide when to cut back black eyed Susans in your garden. 

When is the best time to cut back black eyed Susans?

Black eyed Susans have a long blooming season and can flower all the way from midsummer through until the first frosts. With deadheading, this flowering season can be extended as it will stop the plant going to seed and divert its energy back into producing and opening new flower buds. These bright and simple-to-grow plants do have fantastic flowers that attract bees, pollinators, and other beneficial insects into a space and are worthy of a place in any sunny flower bed, border, or container garden.

The blooming period will come to an end in fall and then the decision comes for when to cut back black eyed Susans. There are two options for when to get out the pruning shears, either to cut them back for winter in the fall or wait until the following spring.

Quinten O’Dea, a professional landscaper, says: ‘the best time to cut back black eyed Susans is in the fall’. He adds: ‘The flower benefits from a strong perennial root system that can withstand trauma and pruning easily. In late summer or fall, cut back these plants at their base, when they've browned a bit and lost their flower petals. 

‘It is difficult to cut these back at the wrong time; their hardiness will have them coming back until they are pulled out of the ground completely.’

Cutting back plants in the fall helps to tidy and neaten the garden for winter, while removing the seed heads will prevent black eyed Susans self-seeding all over the garden – something they are famed for doing. 

The alternative is to leave the plants in situ over winter. Louise Curley, gardens expert, explains how, when the flowers start to fade on black eyed Susans, the central cone remains in place and this can make an attractive and wildlife-friendly feature in a winter garden.

She says, 'If the seedheads are left to stand over winter birds such as goldfinches will eat the seeds. These provide attractive fall and winter structure, particularly when they’re dusted with frost.’

While seed heads in winter can be useful as part of wildlife garden ideas, it likely will mean the plant reseeding around the garden. Some people may be put off by this, however others may not mind extra plants for free or be undeterred if they have a looser and wilder style of backyard ideas. Fear not, however, as if a clump does get too big it is simple to lift and divide plants in spring.

Quinten O’Dea

Quinten O’Dea is a professional landscaper with over 13 years of experience completing quality projects. His company Q&A Landscaping has been planting flowers, shrubs and trees for over a decade now throughout the Pittsburgh area.

How far should you cut down black eyed Susans?

It is important to use clean and sharp pruning shears when cutting back plants, as clean garden tools prevent damaging the plant and spreading diseases around the garden. A pocket sharpener, such as this garden tool sharpener available at Walmart, is a useful piece of kit to help you keep tools sharp while out working in the garden.

Cutting back black eyed Susans is a simple process and the aim is to trim all the stems to a height of around 4-6 inches above the ground. This removes all of the spent flower stems and also most of the plant’s foliage. If you are cutting back the plants for winter, then leaving a few inches of material at the plant’s base will help to protect the crown from the worst of the winter weather.

Zahid Adnan, gardener and founder of The Plant Bible, recommends that a ‘light feeding’ in spring after cutting back the plants can be beneficial too. He says: ‘You can apply a balanced, slow-release fertilizer around the base of the plants. This will help replenish nutrients in the soil and support the plant's growth during the next growing season. Just be careful not to over-fertilize, as this can lead to excessive leaf growth at the expense of flower production.’

An example of a balanced, slow-release fertilizer that would fit the expert's recommendation is the Expert Gardener Flower Plant Food also available at Walmart.

Zahid Adnan

Zahid Adnan is the Founder and Editor of The Plant Bible, as well as managing a plot of 10-hectare agricultural land. He is also involved in a project to develop sustainable urban farming practices by utilizing farming technologies to increase food production and reduce environmental impacts.

FAQs

Black eyed Susans are also a good option when planning a cut flower garden. The blooms are prevalent come late summer and their deep colors work fantastically in displays. If you are looking for cutting garden flowers that have a distinctive appearance and long vase life, then black eyed Susans are well worth consideration.