In the swirling cosmos of bulbs, alliums are the bright, stately planets of the garden. Alliums are never the first spring-flowering bulbs to bloom, but they are perhaps the season's most formidable flower.
Alliums are the ornamental cousins of onions; their flowers are characteristically clusters of blooms, often forming tight globes, but sometimes arranged in loose bunches of pendant bells, like tassles. Tall alliums, particularly 'Gladiator', which has purple flower-heads the size of a soft-pitch softball and stands every inch of 4 feet tall among the peonies, are not for shy gardeners, but the vast world of alliums also has a demure side.
The variety within the genus allium is astounding: about 700 species are known. Little Allium moly, sometimes called golden garlic, grows to only about a foot tall and produces dancing clusters of bright yellow flowers in early summer. Allium aschersonianum has very dark pink flowerheads about the size of a tennis ball and stands about two feet tall. Allium rosenbachianum, one of the earliest alliums to bloom, has round, five-inch flowerheads of purple, white, or a rich lilac. Even after the blooms fade, most allium flowerheads remain quite showy on their tall wands through early summer.
Allium flowers rarely smell like onions — it's the foliage that smells strong, and only when you crush it. They are all easy to grow; few spring-flowering bulbs are as undemanding as alliums. They bloom profusely in full sun, but tolerate a surprising amount of shade. Alliums can thus be planted to advantage among roses, peonies, hostas, and ferns and under trees and around shrubs. Small alliums make a lacy edge at the front of a border: chives, which are easy to grow from seed, make a perfect edging for an herb garden, and they look pretty in front of roses, in a rock garden, or along the edge of a flower bed, too. The largest alliums are like garden sculptures; they're tall enough to plant at the back of a flower bed, but put a few bulbs up front, too: you'll want to shake them by the stems, pat their fuzzy heads, and inspect their thousands of sparkling flowers up close.
How to Sow
Planting Bulbs in Fall:
- Choose a location in full sun with a rich, well-drained soil. Alliums are long lived plants so be sure to choose a location where they may grow undisturbed for many years.
- Prepare the bed by turning the soil under to a depth of 6-12 inches removing any debris, and lightly raking as level as possible.
- The addition of organic matter (leaf mold, compost, well-rotted manure) benefits all gardens and is essential in recently constructed neighborhoods.
- It is a good idea to add fertilizer, such as bonemeal, when you prepare the soil. Be sure to mix the fertilizer into the soil so it does not come into direct contact with the bulbs.
- The general rule for planting is to cover the bulb with soil to 3 times its vertical diameter. In very cold climates, or where the soil is very light and sandy, plant a little deeper. In heavy soils, or in areas with a high water table, plant slightly more shallowly. Plant all bulbs of a kind, when grouped together, at the same depth so they will bloom at the same time and attain the same height.
- For planting clumps of bulbs in beds and borders, dig a hole large enough to hold all the bulbs in one group or drift. Set them upright at the bottom of the hole, tops up (pointed side up), and space properly. Press the bulbs into the soil and cover with the prepared soil to the recommended depth. You can also use a trowel to dig individual holes.
- Alliums should be planted 3-6 inches apart, 4-6 inches deep.
- After planting water thoroughly to settle the soil and to encourage the start of root growth. Sufficient moisture is vital to the health of your bulbs; lacking ample rain, it may be necessary to water new plantings once a week in fall. The roots will continue to grow in fall until the soil freezes.
- Be sure to mark where you planted your bulbs so you know where they are in spring.
- Add 1-3 inches of mulch for winter protection after the ground freezes.
Planting Potted Plants in the Garden:
- Select a location in full sun with rich, well-drained soil.
- Prepare the bed by turning the soil under to a depth of 6-12 inches removing any debris, and lightly raking as level as possible.
- The addition of organic matter (leaf mold, compost, well-rotted manure) benefits all gardens and is essential in recently constructed neighborhoods.
- Plant on a cloudy day or in late afternoon to reduce transplant shock.
- Dig a hole for each plant large enough to amply accommodate the root ball.
- Unpot the plant and gently loosen the root ball with your hands to encourage good root growth.
- Place the top of the root ball even with the level of the surrounding soil. Fill with soil to the top of the root ball. Press soil down firmly with your hand.
- Use the plant tag as a location marker.
- Thoroughly water and apply a light mulch layer on top of the soil (1-2 inches) to conserve water and reduce weeds.
How to Grow
- Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their germination.
- Mulches also help retain soil moisture and maintain even soil temperatures. For perennials, an organic mulch of aged bark or shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time. Always keep mulches off a plant’s stems to prevent possible rot.
- Careful watering is essential in getting perennials off to a good start. Water thoroughly at least once a week to help new roots grow down deeply. Soil should be damp at about 1 inch below the soil surface. You can check this by sticking your finger in the soil. Water early in the morning to give all leaves enough time to dry. One inch of rain or watering per week is recommended for most perennial plants. You can check to see if you need to add water by using a rain gauge.
- Until plants become established, some protection from extreme winds and direct, hot sunlight may be necessary. Good air movement is also important.
- After new growth appears, a light fertilizer may be applied. Keep granular fertilizers away from the plant crown and foliage to avoid burn injury. Use low rates of a slow release fertilizer, higher rates may encourage root rots.
- Remove and discard foliage after a hard frost in fall.
- In general allium clumps may be left undisturbed for years and only need to be divided when they are too crowded to blossom freely.
Growing Tips
- Alliums make wonderful, long lasting cut flowers.
- Alliums flower from spring to summer depending on the variety.
- Alliums may also be planted in containers.
Common Disease Problems
Bacterial Soft Rot: This is mostly an issue with on mature bulbs. Affected bulbs first appear water-soaked and pale yellow to light brown or bleached gray to white. As the disease progresses, infected tissue becomes soft and sticky with the interior of the bulb breaking-down. A watery, foul-smelling thick liquid can be squeezed from the neck of diseased bulbs. It is spread by water and some insects through wounds on the plant. Burpee Recommends: Avoid overhead watering where possible, and control insect pests such as onion maggot, that can spread it.
Downy Mildew: This fungus causes whitish grey patches on the undersides and eventually both sides of the leaves. Burpee Recommends: Rotate crops with plants in a different family. Avoid overhead watering. Provide adequate air circulation, do not overcrowd plants. Do not work around plants when they are wet.
Onion White Rot: This soil-borne fungus causes yellowing and wilting of foliage above ground. Below ground, the roots rot and the fungus also infects the bulb. At the base of the bulb, a white fluffy fungus will appear with black fungal bodies. Burpee Recommends: Remove infected bulbs. Practice crop rotation with members of the onion family.
Common Pest and Cultural Problems
Leafminers: These insects bore just under the leaf surface causing irregular serpentine lines. The larvae are yellow cylindrical maggots and the adults are small black and yellow flies. They do not usually kill plants, but disfigure the foliage. Burpee Recommends: Remove affected foliage.
Onion Maggot: This insect causes damaged roots and bulbs. The adult is a greyish colored fly which lays its eggs around the base of the plant. The maggots bore into the roots. Burpee Recommends: Remove all bulbs at the end of the season and remove all volunteer wild onion plants. Floating row covers can prevent the females from laying eggs. Check with your Cooperative Extension Service for pest controls.
Slugs: These pests leave large holes in the foliage or eat leaves entirely. They leave a slime trail, feed at night and are mostly a problem in damp weather. Burpee Recommends: Hand pick, at night if possible. You can try attracting the slugs to traps either using cornmeal or beer. For a beer trap, dig a hole in the ground and place a large cup or bowl into the hole; use something that has steep sides so that the slugs can’t crawl back out when they’re finished. Fill the bowl about ¾ of the way full with beer, and let it sit overnight. In the morning, the bowl should be full of drowned slugs that can be dumped out for the birds to eat. For a cornmeal trap, put a tablespoon or two of cornmeal in a jar and put it on its side near the plants. Slugs are attracted to the scent but they cannot digest it and it will kill them. You can also try placing a barrier around your plants of diatomaceous earth or even coffee grounds. They cannot crawl over these.
FAQ
Do alliums make good cut flowers? Yes, they make long lasting cut flowers. The onion smell will go away once the flowers are placed in water.
Can you dry allium flowers? Yes, leave the flowers in the garden and allow to dry on the stalks, then cut the flowers for indoor arrangements.
Are alliums deer resistant? Yes, deer do not generally eat alliums, however if deer are very hungry they may eat them.
How late can I plant the allium bubs in the fall? Ideally the bulbs should be planted at least 6 weeks before the ground freezes.