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The two ways to propagate alliums are through dividing the bulbs and through collecting and sowing the seeds. I cover both these methods in this article.
Dividing the bulbs
Propagate alliums by dividing the bulbs in early to mid-autumn. Wait until the flowers and leaves have died back.
Dig around the plants you want to divide with a trowel. Dig at about 8cm from the bulb clump. It’s a good idea to take these from all around your allium bed. This creates more space for the other plants to grow and also helps to improve air circulation.
Lift up each plant with its bulbs and roots. There should be a collection of bulbs all together for the plant.
Gently separate out the smaller bulbs with your hands taking care not to harm the roots. Discard any bulbs which become damaged.
If you wish, place a few of the bulbs back in the original space. Transplant the rest in new places in your garden. See my article When and how to plant and grow alliums for information on how to do this.
Collecting and growing seed
The second method to propagate alliums is to collect the seed from your own allium plants. If your plants are hybrids then any new plants grown from the seed will be different in colour and shape to the original.
Remove the seeds when they appear. If you’re not going to sow them straight away, keep them in your fridge.
When you’re ready, distribute the seeds into trays of mixed grit and compost or potting mix. Remember good drainage is essential right from the start for alliums.
Cover the seeds with 5cm of compost as protection. Water them well, ensuring that the trays are draining fully.
Wait for the seeds to germinate, about 12 weeks but it could be longer. And then transplant them into individual pots.
Note that alliums grown from seeds could take several years to flower.