Allium Guide: How to Grow & Care for “Ornamental Onion”

Read our guide to Allium Flowers for everything you’ll ever need to know! Tips for planting & caring for "Ornamental Onion"

Read our guide to Allium for everything you will ever need to know! Tips for planting & caring for Ornamental Onion.

Allium, commonly known as ornamental onion, is a great flower to have in your outdoor space. It won’t spice up your meals but it will definitely look amazing in your garden. Featuring lovely pom-pom lilac-purple flowers, ornamental onions create a dramatic appearance when planted en masse in gardens. In addition to that, these flowering plants attract bees and other pollinators like magnets.

Ornamental onions have a bold and architectural appearance that lasts from spring to summer. They look best in sunny borders or combined with feathery ornamental grasses. Since they also make great cut flowers, you can also use them fresh or dried in floral arrangements.

These flowers are also edible. The bulbs and leaves are usually consumed. These parts of the flower contain several organic compounds, including organosulfides, which give them a unique odour and taste.

Alliums are also extremely tough plants that can withstand both drought and freezing temperatures. Deer or rodents will not bother them either. And most importantly, they are extremely easy to care for.

Ready to learn more about how to grow and care for Ornamental Onions? Keep reading our guide!

About Ornamental Onion

  • Allium belongs to the family of Amaryllidaceae, a family of herbaceous, including perennials and bulbous plants.
  • The botanical name of the ornamental onion is Allium, which is also the Latin word for garlic.
  • There are over 700 different species of ornamental onions. The majority of Allium species are native to the Northern Hemisphere, predominantly to central Asia.
  • Ornamental Onions look fantastic in gardens, thanks to their bright purple colour. They look best when combined with other plants that have a finer texture, such as ornamental grasses. The leaves of Ornamental Onions aren’t particularly beautiful and start to deteriorate even before the plants have flowered, which is why it’s best to hide their foliage behind a denser plant.
  • Ornamental Onions also look amazing as cut flowers if you want to bring them inside your home or use them in flower arrangements fresh or dry.
  • These flowers are sun-loving and thrive in full sun. It’s best to plant Ornamental Onions in a sunny spot of your garden where they will get full sun the entire day.
  • In terms of soil preferences, Allium plants prefer a soil pH that is slightly acidic, something like 5.5 to 6.5. The soil needs to allow good drainage so that the bulbs won’t rot.
  • Most species of Alliums are hardy to extremely cold temperatures, like – 20 to -30 °F ( -28- -34 °C). They are also drought-tolerant in times of scorching temperatures.
  • When it comes to water needs, Alliums prefer infrequent watering. If you live in an area where it rains frequently, the rainwater should be enough. If not, you should only water these flowers every three to five days.
  • Ornamental onions aren’t considered toxic to humans, but they can cause upset stomach and digestion problems if ingested, so it’s best not to cook with these plants.
  • Ornamental onions are toxic to pets if ingested because they contain organic sulfur compounds, which can turn into highly reactive oxidants once they reach the intestinal tract. Some symptoms of poisoning in pets include elevated heart and respiratory rates, loss of consciousness, lethargy, diarrhoea, and abdominal discomfort. Make sure you plant these flowers in an area or your garden that’s out of your pets’ reach.
  • Alliums are particularly sensitive to bulb rot and other fungal diseases if kept in extremely moist soil. Another threat can be snails and slugs and allium leaf miners. Other than that, these plants, like their culinary cousins, are pretty resistant to different threats like pests, deer, or rodents.

Ornamental Onion Features: An Overview

  • Alliums feature pungent linear leaves and pom-pom flowers that come in a range of colours, including lilac-purple, white, pink, yellow, and green. Most commonly planted Ornamental Onions feature purple flowers.
  • The flowers of Alliums also feature black seeds in dry capsule fruits.
  • Ornamental onions bloom in late spring, and their flowers remain until later summer. Some species of Allium are fall bloomers.
  • Depending on the species, some ornamental onions can reach heights of up to 1-4 feet (30-120 cm) tall and 3-10 inches wide (7-25 cm).

Growing Ornamental Onion

Growing and caring for Ornamental Onions isn’t difficult. These flowers are very resistant to many threats that the average garden plants are sensitive to. They can survive extreme temperatures, both hot and cold, and very few pests and diseases can bother them.

As long as you provide them with their basic growing needs, caring for ornamental onions will be a piece of cake. Thanks to the fact that they are low-maintenance, Alliums can be grown by novice and experienced gardeners too.

First things first, it’s essential to remember that these plants love growing in full sun. In fact, they need at least 6 hours of full sun daily to bloom and thrive. They also need 4-6 hours of partial sun and about 4 hours of full shade. If you can find a spot in your garden that is sunny most of the day and gets partial shade in the afternoon, your Ornamental Onions will be really happy.

Fertilizing your Alliums is another trick to help them thrive and fill your outdoor space with bright colours. Depending on how often you amend their soil, you may not need to feed them that often or even at all. However, if the soil in your garden is less than ideal for these flowers, it is best to help them with a little balanced fertilizer during the blooming time. This will help your ornamental onions replenish the energy they use in the flowering process.

Pruning is also necessary to help your Alliums stay happy and healthy. We recommend cutting wilted flower scapes as they die off. Make sure that you cut the stem off as short as possible. It’s also a good idea to cut leaves back after you notice that they have turned yellow. This helps these flowers as this is the moment when the bulb is stocking up on nutrients that are needed for the next cycle of flowering.

10 Dark Purple Allium Bulbs, From Amazon

Planting Ornamental Onion

Planting Ornamental Onions in your garden is just as easy as caring for them. There are just a few things you need to keep in mind to ensure successful planting.

First of all, make sure that you plant the bulbs in the fall. Keep in mind that the planting depth should be two to three times bigger than the diameter of the bulb. So, for example, if you have a bulb that has a diameter of 2 inches, plant the bulb at a depth of 4 to 6 inches. Water the bulbs well after planting them.

Another important thing to remember is that you’ll need to find the right spot to plant your ornamental onions. These flowers need to be planted in an area of your garden where they get full sun most of the day.

Watering Ornamental Onion

It is essential to know just how much water to give your Ornamental Onions.

Ornamental onions are very susceptible to bulb rot if they sit in too much water. And, this is a sure way to kill your Alliums. In contrast, they don’t mind periods of drought that much. So, it’s best to underwater your ornamental onions than to overwater them.

These flowers prefer infrequent watering, and if you live in an area where rain does much of the work of watering your garden, you’re all set. You only need to water your Alliums every three to five days if your area doesn’t get rainy too often.

To make sure that you don’t overwater your ornamental onions, we recommend using the “soak and dry” watering method. This means that you should only water your Alliums when the top few inches of the soil are completely dry.

Propagating Ornamental Onion

If you want more ornamental onions in your outdoor space, which you should because they look great when planted en masse, the good news is that propagation isn’t a challenging process either when it comes to these flowers.

Ornamental onions can be propagated by dividing the clumps of bulbs in spring or fall. The small offsets you take from the original bulb need to be replanted immediately, and they might require a more extended period, a couple of years, to flower. The rhizome forming alliums, however, can be planted anytime.

You can also propagate these flowers using seeds. However, it may take longer for the flower to grow to an appropriate flowering size. When using seeds for propagation, keep in mind that the germination process will take from 14 to 21 days.

Ornamental Onion
Ornamental Onion

In Conclusion

Ornamental Onions are a joy to have in any outdoor space. When they start blooming in late spring, they fill your garden with bright colours and attract beautiful pollinators like bees and butterflies, which are good news for your other plants too.

It isn’t difficult to care for Alliums as they are resistant to several threats specific to garden plants. What’s more, they only require a lot of sunlight and some water from time to time to be happy and healthy.

Are you growing ornamental onions in your garden? Let us know in the comments below!

Miruna is an experienced content writer with a passion for gardening. She is the proud owner of an outdoor rose garden and an indoor collection of tiny succulents. She bought her first succulent 10 years ago - an adorable Echeveria Setosa. Now she owns more than 100 succulents and cacti of different colors, shapes, and sizes. Miruna is a versatile writer and, as you might have guessed, her favorite topic is gardening. Contact

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