Growing Rudbeckia From Seed - Cornflower Propagation

Last updated on May 3rd, 2022

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The Black-Eyed Susan, also known as Rudbeckia or Cornflower, is a very popular plant and is not to be confused with the Black-eyed Susan vine which is a climber.

It is well known for having bushy and colourful yellow flowers with a black centre from around July until around October. These look very similar to daisies but have a cone in the middle. You can find varieties that are annuals, biennials and even perennials with one of our personal favourites being Rudbeckia fulgida ‘Goldstrom’. Planting perennial Rudbeckia means you get them year after year, however, being perennial they do die back for the winter. Of course, if you already have successful plants in your garden you might want to propagate more by taking the seed and propagating them.

But where do you begin with Cornflower propagation?

How to sow and grow Rudbeckia from seed

If you are going to grow Rudbeckias from seed, the rules are pretty similar for annuals and perennials, and the process is the same.

Sowing annual Rudbeckia from seed

Step 1

If you are sowing annuals from seed, you want to begin the process between February and April. Place the seeds in a pot or a tray full of quality seed compost. You want to keep the temperatures between 20°C and 25°C. You can improve your success rate by starting them off in a heated propagator, but if not, you can start them off on a warm windowsill or in a heated greenhouse.

Step 2

You should keep them in an area that’s very similar to greenhouse conditions, warm with indirect sunlight, and water them only as much as necessary. Overwatering can be very damaging at this stage. You want to keep the compost moist but not too wet.

Step 3

Once your seedlings are large enough to be grown in pots (between 7.5cm and 9cm in size) they are ready to go outside. However, if there is still a chance of frost we recommend keeping them indoors for a little longer. Until then, you might want to consider giving them slightly larger and subsequently larger containers until they reach that point. However, this is not a requirement and they will soon put on plenty of growth when planted outdoors.

Sowing perennial Rudbeckia from seed. These offer flowers year after year

If you are sowing perennials from seed you can do it between February and July, meaning they can be sown a little later than annuals. You want to maintain temperatures between 18°C and 20°C. You should keep them in an area that’s very similar to greenhouse conditions like you would annuals, warm with indirect sunlight, and water them only as much as necessary.

Once your seedlings are large enough to be grown in single pots, we recommend growing them in a 9cm to 1-litre pot until they are rooted before permanently planting them outdoors. It is safe to move your new plants outside once the danger of frost has passed, usually around April / May. You just want to avoid damaging the new growth with a late frost.

How to care for them

After you have successfully grown your Rudbeckia from seed and transplanted them into the ground after growing them on for a few weeks, make sure that you give them an area that has access to full sun or at least partial sun.

You can enrich the soil with extra organic matter, if you have a compost heap this will work great, and add mulch around the plant to help with moisture retention while they root. It’s important that no matter where your new plants end up, they have access to food and water but are never waterlogged because they need well-drained soil.

Learn how to improve drainage in your garden in this guide.

Once they reach the appropriate size, you can move them outside in the autumn if you have sown the seed later or the spring if you have sown the seeds early.

Make sure you dig a hole that’s big enough for the root ball and when you place the plant in the ground or in a container, make sure that the crown of the leaves remains level with your compost and backfill the area. Add some granular slow-release plant food and add a thick layer of mulch (about 5cm thick) and water it well. Try to keep the soil moist but allow the surface of the soil to dry out slightly before watering again.