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Growing Rudbeckia from seed – Cornflower Propagation
Last Updated on March 25, 2020 by John
The Black-Eyed Susan, also known as Rudbeckia or corn flower, is a very popular plant and should 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 that looks very similar to daisies but has the cone in the middle. You can find varieties that are annuals, biennials and even perennials with our favourite being Rudbeckia fulgida ‘Goldstrom’ so that you get them year after year but being perennial they do die back for 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 how do you go about cornflower propagation?
How to sow and grow Rudbeckia from seed
If you are going to grow from seed, the rules are pretty similar for annuals and perennial and the process is the same.
Sowing Annual Rudbeckia from Seed
If you are sowing annuals from seed, you want to start 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 degrees Celsius and 25 degrees Celsius so you can improve the success rate buy starting them off in a heated propagator but if not you can start them off on a warm windowsill or heated greenhouse.
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. Over-watering can be very damaging at this stage but you want to keep the compost moist but not wet.
Once your seedlings are large enough to be grown in pots between 7.5 cm and 9cm in size, they are ready to go outside but if there is still a chance of frost outside we recommend keeping in inside for a little longer. But until then, you might 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 that offer flowers year after year
If you are sowing perennials from seed you can do it between February and July so they can be sown a little later than annuals. You want to maintain temperatures between 18 degrees Celsius and 20 degrees Celsius. 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 rooted before planting outdoors when 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, also known as cornflowers 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 rooted. It’s important that no matter where your new plants end up, they have access to food and water but are never waterlogged as they need well-drained soil.
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 were sowing seed 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, add a thick layer of mulch about 5cm thick, and water it well and try to keep the soil moist but allow the surface of the soil to dry out slightly before watering again.
Top Rudbeckia varieties to try
There are many varieties from which to choose.
- Rudbeckia hirta ‘Cappuccino bronze’
- Rudbeckia hirta ‘Cherry Brandy’
- Rudbeckia hirta ‘Prairie Sun orange’
- Rudbeckia hirta ‘rustic dwarf’
- Rudbeckia hirta ‘Toto dwarf’
- Rudbeckia fulgida ‘goldstrom’
- Rudbeckia laciniata ‘herbstsonne Golden’
Last update on 2020-09-19 at 16:02 / Affiliate links / Images from Amazon Product Advertising API