Alliums are a genus of ornamental flowering bulbs that include popular varieties like garlic, onions, leeks and shallots. With their unique, spherical blooms atop slender stems, alliums make excellent additions to flower gardens and borders. This comprehensive guide provides tips and techniques for successful alliums gardening, to enhance the beauty of your outdoor space.
Understanding Alliums
Alliums belong to the Amaryllidaceae family and are known for their ornamental value. The genus contains over 800 species, including culinary favorites like garlic, onions, leeks, and chives.
These plants are characterized by their spherical or dome-shaped flower heads that sit atop long, slender stems. The foliage is slender and grass-like in texture.
Some of the most popular allium varieties grown for ornamental purposes include:
- Purple Sensation
- Globemaster
- Gladiator
- Schubertii
- Drumstick allium
- Azureum
- Millenium
The blooms come in shades of purple, pink, blue, yellow, and white depending on the variety. The heights range from dwarf varieties under 12 inches, to tall kinds reaching 4 feet high.
Benefits of Alliums
There are many great reasons to practice alliums gardening:
- Visually striking flowers that add elegance and sophistication
- Long blooming period, usually 4-6 weeks
- Low maintenance and easy to grow
- Deer and rodent resistant
- Attract pollinators like bees and butterflies
- Fragrant flowers on some varieties
- Wide versatility in garden design and containers
With their long-lasting blooms and visually captivating spheres of color, alliums provide plenty of ornamental value and enjoyment in the garden.
Choosing the Right Allium Varieties
When selecting allium bulbs for your garden, keep in mind factors like bloom time, flower color, plant height and growing conditions.
Bloom Time
Choose early, mid and late-season bloomers to enjoy flowers from spring through fall. Some examples:
- Early bloomers: Allium moly, Azureum
- Midseason bloomers: Purple Sensation, Globemaster
- Late bloomers: Gladiator, Millenium
Staggering varieties will provide continuous color and interest in your garden for months.
Flower Color
Alliums provide a wide spectrum of rich and dazzling colors:
- Purple: Sensation, Globemaster, Gladiator
- Pink: Schubertii, Gladiator
- White: Mount Everest
- Yellow: Moly luteum
- Blue: Azureum
Mix colors together or plant in solid drifts for different effects.
Plant Height
Select a combination of tall, mid-height and dwarf alliums:
- Tall: Globemaster, Gladiator, Purple Sensation (2 to 4 feet)
- Mid-height: Schubertii, Millenium (1 to 2 feet)
- Dwarf: Moly, Drumstick (6 to 12 inches)
Varying heights creates dimension and visual interest.
Growing Conditions
Factor in site conditions when choosing varieties:
- Full sun lovers: Purple Sensation, Mount Everest
- Partial shade tolerant: Millenium, Azureum
- Wel-drained soil: Globemaster, Gladiator
- Moist soil tolerant: Drumstick
Select types suited for your unique garden environment. By considering these factors, you can pick the best allium varieties for your particular needs and conditions.
Preparing the Garden for Planting
Proper planning and preparation of your garden beds ensures healthy, thriving alliums. Follow these tips to get your site ready for planting.
Selecting the Right Location
When preparing a spot for alliums, consider the following factors:
- Sunlight: Most alliums need full sun – at least 6 hours of direct sunlight per day.
- Soil drainage: Good drainage is key to prevent bulb rot. Avoid low, wet areas.
- Soil pH: Alliums prefer slightly acidic to neutral soil with a pH of 6.0-7.0.
- Air circulation: Space bulbs adequately to allow air flow between plants.
- Protection: Shelter bulbs from strong winds which can damage stems.
Select a site that meets the sun, drainage and soil pH needs of the varieties you want to grow.
Preparing the Soil
Follow these tips to prepare soil before planting:
- Loosen soil at least 8-12 inches deep using a shovel or garden tiller. Allium bulbs develop deep roots.
- Mix in 2-4 inches of compost or well-aged manure to improve fertility, drainage and moisture retention.
- Check pH levels with a soil test and amend if needed. Add lime to raise pH or sulfur to lower it.
- Rake beds smooth to create an even planting area free of debris.
- Consider adding a granular bulb fertilizer at planting time to give roots an extra nutrient boost.
Rich, loose, well-draining soil gives allium bulbs the best start. Take time to properly prepare beds for optimal growth.
Planting and Caring for Alliums
With the right planting techniques and proper care, your alliums will thrive and brighten your garden with their delightful blooms.
When to Plant the Bulbs
Allium bulbs are planted in the fall, typically late September to November. Planting in autumn allows root establishment before winter dormancy. Bulbs need the cold period to initiate flowering in spring and summer.
If winters are very cold, add an extra layer of mulch over the bulbs for insulation and frost protection. Remove mulch after the ground thaws in spring.
How to Plant the Bulbs
Follow these steps when planting allium bulbs:
- Dig holes 2-3 times the height of the bulb. Taller alliums are planted deeper than smaller ones.
- Space bulbs 4-8 inches apart depending on variety. Closer for dwarf types, wider for larger bulbs.
- Place bulbs root side down in holes with pointy tips facing up.
- Backfill holes with soil and press gently around bulbs.
- Water thoroughly after planting to settle soil and spur root growth.
Proper planting depth and spacing is key for healthy plants.
Watering and Irrigation
Consistent watering is crucial, especially after planting in fall and during the active growing season in spring:
- Give bulbs a deep soaking after planting and weekly thereafter until ground freezes.
- In spring, provide 1-2 inches of water weekly as plants start actively growing.
- Avoid wet foliage, which can promote diseases – water at soil level.
- Use drip irrigation, soaker hoses or watering wands rather than sprinklers.
- Drought resistant varieties may need less frequent watering. Check soil moisture before watering.
- Reduce watering frequency after blooms are spent and plants die back.
Proper moisture is vital for plump bulbs and abundant blooms. Monitor rainfall and soil moisture to determine watering needs.
Fertilization
Apply a balanced bulb fertilizer or all-purpose plant food to support growth:
- Fertilize at planting time to stimulate root development.
- Make a second application in early spring when growth resumes.
- Liquid or granular fertilizer can be used. Follow label directions.
- Place fertilizer around the bulb, not directly on it.
- Overfertilization can cause floppy growth and leaf burn.
Fertilizer boosts nutrients for optimal flowering and performance. Feed bulbs at the right times for best results.
Pests and Diseases
Alliums gardening is relatively trouble-free, but may be affected by:
- Onion maggots – Control with insecticidal soap or neem oil.
- Onion thrips – Dislodge with streams of water. Apply spinosad insecticide if severe.
- Botrytis or downy mildew – Improve air circulation between plants. Avoid wet foliage.
- Bulb mites – Remove and destroy infested bulbs to prevent spreading.
- Rodents – Use hardware cloth to line planting holes to prevent nibbling.
Careful inspection, prompt treatment and proper cultivation help prevent problems. Maintain vigilant garden sanitation for healthiest plants.
Cutting Back Spent Flowers
Deadhead or trim back faded blooms to:
- Promote longer flowering on some varieties.
- Prevent self-seeding which saps bulb energy.
- Maintain a tidy appearance.
- Allow pollinators access to remaining flowers.
- Funnel energy back to bulb for future growth and flowering.
Use sharp pruning shears or garden scissors for easy deadheading.
Post Bloom Care
After the flowers fade, the foliage and stems die back:
- Allow foliage to yellow and die back naturally after blooming.
- Avoid cutting back leaves until they turn brown – the greenery still produces nutrients for the bulb.
- When leaves die back, they can be removed or kept for continued ornamental interest in the garden.
- Stop watering and let soil dry out once foliage starts yellowing.
- Fertilize bulbs again in late summer or fall to replenish nutrients after flowering. Apply compost as mulch.
- Lift and divide overcrowded clumps every few years after bloom season.
Proper care after flowering ensures bulbs store energy and nutrients for future growing seasons.
- For neatest appearance, foliage can be tied & braided, or cut back.
- But leaving foliage in place allows leaves to photosynthesize. This channels more energy back to bulbs.
- If cutting back, do so only after leaves completely yellow or brown.
- Let foliage die back naturally without premature removal for plumpest bulbs.
Popular Allium Varieties to Grow
Many stunning allium varieties exist. Here are some top picks for your garden:
Purple Sensation
One of the most widely grown alliums, Purple Sensation produces 2-3 foot stems topped with large, rounded deep purple blooms 4-6 inches wide. Flowering in late spring, the vibrant blossoms last 4-6 weeks, injecting color in the garden. This variety does best in full sun and well-drained soil. The eye-catching blooms also attract bees, butterflies and other beneficial pollinators.
Globemaster
Globemaster allium is prized for its huge, spherical purple flower heads up to 8-10 inches in diameter. Growing 24-36 inches tall, each plant can produce up to two dozen blooms. This mid-season bloomer thrives in full sun to part shade and moist, fertile soil. The large, distinctive flowers make a dramatic statement in borders or containers. Globemaster has excellent weather resistance.
Schubertii
Schubertii offers uniquely shaped blossoms with star-shaped petals in shades of pink to purple. Flower heads can reach 8 inches across, consisting of up to 50 individual flowers clustered together in a fireworks style display. Plants reach 18-24 inches tall. Schubertii prefers full sun and neutral to slightly alkaline soil. The unusual blooms make a fun addition to garden beds and bouquets.
Mount Everest
A taller variety reaching 3-4 feet high, Mount Everest has large, spherical flowers of pure white. The pristine blooms contrast nicely against the green foliage. Mount Everest does best in full sun and slightly acidic soil with a pH between 6.0-6.5. The majestic white spheres look elegant in perennial borders and cut flower arrangements. This variety also has excellent heat and drought tolerance once established.
With hundreds of allium species and cultivars to choose from, you’re sure to find many fantastic options. Mix heights, colors and bloom times for an appealing display.
Design Tips for Planting Alliums
Alliums provide gorgeous structure and ornamental value. Here are some design tips:
- Plant in drifts or clusters for bold splashes of color.
- Mix early and late bloomers for extended color.
- Combine taller varieties behind shorter ones.
- Grow alliums in borders, beds, containers and rock gardens.
- Allow plenty of space between bulbs for air circulation.
- Underplant bulbs with low-growing perennials and annuals.
- Use alliums as edging along paths, walls and fences.
- Interplant with salvias, irises and ornamental grasses.
- Feature in pollinator-friendly gardens to attract bees.
Get creative with these versatile bulbs! Combine with perennials, roses, herbs and more.
Companion Plants for Alliums
Here are some great options to pair with alliums:
Large perennials: Astilbe, hostas, daylilies, garden phlox, yarrow, garden roses. These provide height contrast and fill in once allium foliage dies back.
Midsize perennials: Catmint, coral bells, lavender, salvia, daisies, veronica. These mingle nicely without overpowering.
Grasses: Blue oat grass, purple fountain grass, maiden grass, buffalo grass. Grasses offer movement and texture contrast.
Annuals: Marigolds, zinnias, cosmos, bachelor buttons. Quick-growing annuals supply continuous color around alliums.
Bulbs: Tulips, daffodils, crocus, hyacinths. Layer together for prolonged spring blooms.
Herbs: Chives, thyme, oregano, parsley, sage, lavender. Herbs offer scent and culinary use.
Get creative combining alliums with other plants. They pair beautifully in mixed beds and borders.
- Underplant purple alliums with white daisies for contrast.
- Alternate blue-violet Globemaster with bright yellow tulips.
- Surround Allium schubertii with frothy Astilbe in pink or white.
- Accent tall Drumstick alliums with low-growing catmint.
- Edge walkways or borders with neat rows of Purple Sensation.
Have fun playing with color, height and texture as you plan out plant combinations.
Growing Alliums in Containers
Alliums adapt quite well to container culture. Follow these tips for success:
- Soil: Use a quality potting mix with good drainage. Incorporate bulb fertilizer at planting.
- Drainage: Ensure containers have drainage holes to prevent waterlogging. Add perlite to improve drainage.
- Sun: Place containers in full to part sun. Protect from hot afternoon sun in warmer climates.
- Planting: Choose proportionate containers for bulb size. Plant one variety per pot for best visual impact.
- Water: Check soil moisture frequently and water when surface is dry. Reduce watering once blooms are spent.
- Overwintering: Store dormant bulbs in a cool, dry spot after they finish flowering. Repot in fall for winter growing.
With the right care, alliums thrive beautifully in containers. Display on decks, patios and entryways for easy enjoyment.
Overwintering Allium Bulbs
Allium bulbs are perennial and winter hardy in most climates. To overwinter them:
- Allow foliage to die back naturally after blooming. Continue watering.
- Once leaves brown, cut back and dig up bulbs with foliage attached. Knock off loose soil.
- Spread out bulbs in a single layer in a cool, dry spot with good ventilation.
- Ideal storage conditions are temperatures of 40-50°F and 50-70% humidity.
- Check bulbs occasionally for rotting or pest damage. Discard damaged bulbs.
- After 12-16 weeks, remove faded foliage and plant bulbs at proper depth in fall.
- Apply bulb fertilizer and organic matter like compost when replanting.
Proper storage keeps bulbs healthy so they can re-bloom the following growing season.
Dividing Overgrown Allium Clumps
Mature allium bulbs multiply and form dense clumps over time. To revive overgrown plants:
- Dig up entire clump after foliage fully dies back. Gently pry apart connected bulbs.
- Sort bulbs by size. Discard any that are diseased, damaged or mushy.
- Replant largest, healthiest bulbs 4-6 inches deep and 6-8 inches apart in enriched soil.
- Smaller bulbs can be replanted as well but may not flower their first year.
- Water thoroughly after replanting divided bulbs. Apply high phosphorus fertilizer to stimulate root growth and flowering.
- Dividing overcrowded clumps every 3 years reinvigorates plants for years of beauty.
Dividing and thinning will renew crowded allium plantings. The practice promotes flowering and healthy bulb development.
Troubleshooting Common Allium Problems
While relatively hardy, alliums can sometimes encounter issues. Here’s how to troubleshoot common problems:
Problem: Flowers small and sparse
Cause: Insufficient sunlight; overcrowding; poor nutrition
Solution: Move to sunnier location; divide clumps; fertilize regularly
Problem: Leaves distorted, tunneled or chewed
Cause: Onion maggots, thrips, mites, slugs, snails
Solution: Remove affected foliage; apply insecticidal soap or neem oil; set out bait traps; spread diatomaceous earth
Problem: Flowers rotting or moldy
Cause: Excess moisture; crowded bulbs
Solution: Improve drainage; space bulbs farther apart; avoid overhead watering; increase sunlight
Problem: Weak stems that flop over
Cause: Insufficient sunlight; overfertilization; heavy rains
Solution: Stake or support stems; move to sunnier spot; reduce fertilizer; amend soil to improve drainage
Problem: Failure to flower
Cause: Insufficient chill period; planted too late; planted too shallow
Solution: Plant bulbs earlier in fall; pre-chill bulbs indoors; plant bulbs at proper depth
Problem: Bulbs rotting
Cause: Poor drainage; overwatering; deep planting
Solution: Improve soil drainage; water thoroughly but allow soil to dry between waterings; plant at optimal depth
Catching issues early and making cultural improvements prevents minor problems from escalating. Contact your local extension office for diagnosis of any serious or widespread issues.
Allium Gardening FAQs
Q: What is the best time to plant allium bulbs?
A: Plant allium bulbs in fall about 2-3 months before first hard frost. This allows good root establishment before winter dormancy.
Q: How often do allium bulbs need to be divided?
A: Large, mature allium clumps benefit from division every 3-5 years. Signs it’s time include reduced flowering, crowded bulbs and decline in plant health.
Q: Should allium foliage be cut back after flowering?
A: It’s best to leave foliage in place until it completely dries up. The leaves still produce nutrients that get transported back to the bulb. No need to tidy up plants before the foliage finishes dying back naturally.
Q: How do I keep allium flowers standing tall and upright?
A: Stake taller varieties to prevent flopping, especially in windy or rainy conditions. Plant in groups so stems can support each other. Locate bulbs out of high winds. Maintain optimal growing conditions.
Q: What is the best way to plant allium bulbs in pots?
A: Choose containers with drainage holes, use a quality potting mix, add bulb fertilizer, plant one variety per pot, and water carefully to avoid soggy soil. Move pots to a protected spot for winter.
Got an allium question? Consult our complete growing guide for answers to all your allium gardening FAQs.
Final Thoughts
With their unique floral spheres and fabulous colors, it’s easy to see why alliums are stars of the late spring garden. By choosing varieties suited to your climate and conditions, preparing planting beds properly, and providing attentive care throughout the season, you can achieve allium gardening success. Remember to plant bulbs at the right depth in enriched, well-draining soil. Provide adequate water and nutrition, and remove spent blooms promptly. Mix heights, flower forms and colors for sensational effect. With the insights from this comprehensive guide, you can plant, nurture and enjoy a standout display of alliums. Let these special bulbs bring you joy, beauty and vibrant blossoms for seasons to come.
