Also known as ornamental onions alliums grow in fertile, well-drained soil. Most prefer full sun with the exception of allium ursinum (wild garlic) that thrives in shady woodland settings. Alliums do not thrive in waterlogged ground. If your soil is poor dig in a well balanced fertiliser such as liquid seaweed.
Plant your alliums between September and the end of November. The larger varieties like Allium Ambassador should be planted around 15cm deep and approximately 15 to 20cm apart — allowing for around 10 to 20 bulbs per square meter. The smaller flowering allium, Allium Moly for example, can be planted around 10cm deep and 8cm apart — around 40 to 75 per square meter.
Most alliums will do well in deep pots. Use a John Innes No.3 soil mixed with compost or garden soil with a little added grit. Underplanting with other plants will disguise the dying leaves that can look a little messy. Small hostas are good companions and will provide extra colour throughout the summer months.
To keep your alliums flowering year on year, lift and divide overcrowded clumps after two to three years before removing any tiny new bulbs and planting them in pots or in the garden until the bulbs are mature. It will take them a few years to develop into flowering size bulbs but the wait will be worth it.
Avoid poor flowering results by always unpacking your bulbs on arrival and storing them in a cool place until you’re ready to plant them
Planting your bulbs too shallowly or in wet, soggy soil will also result in poor flowering so do follow the planting advice carefully.
Allium bulbs and plants can be poisonous to cats and dogs. Most animals wouldn’t dream of nibbling on them but do take care to protect your pets.
Potential problems, pests and diseases:
All bulbs from the onion family are susceptible to similar problems such as onion fly, onion white rot and mildew. If you're planting your alliums in an allotment for cut flowers it is important not to plant where onions were previously planted or close to onions in other beds. Slugs and snails are also problems for allium so provide some protection.