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How to Grow Alliums (Garlic & Onions)

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Alliums (Garlic & Onions)

Allium sativum (garlic), Allium cepa (onion)

vegetable

Alliums are cool-season bulb crops prized for their pungent flavor compounds and natural pest-deterrent properties. Garlic and onions are staple kitchen crops that also function as excellent companion plants, repelling many garden pests through their sulfurous compounds. Both are relatively easy to grow and store well for long-term use.

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Example Alliums (Garlic & Onions) timeline · Pittsburgh, PA (Zone 6b)

  1. Plant Alliums (Garlic & Onions)

    Around Apr 17

    Near Pittsburgh's average last spring frost.

  2. Tend & protect

    Late spring–summer

    Watering, feeding, and pest-watch reminders.

  3. Harvest Alliums (Garlic & Onions)

    Around Aug 15

    ≈ 120 days after planting

Sample dates for Pittsburgh, PA. Sign up to get exact Alliums (Garlic & Onions) dates for your own zip code.

Growing Conditions

☀️
Sun: Full sun, 8+ hours daily (garlic needs 8-10 hours for optimal bulb development)
💧
Water: Moderate; 1-1.5 inches per week. Keep soil consistently moist but not waterlogged, especially during bulb formation. Reduce watering as plants mature and approach harvest.
📏
Spacing: 4-6 inches apart in rows 12-18 inches apart (garlic); 3-5 inches for onions inches
📅
Days to maturity: 120-180 days for garlic (fall plant, spring harvest); 90-120 days for onions (spring plant, summer harvest)
🌱
Planting depth: Plant cloves 2 inches deep (garlic); seeds/sets 1-1.5 inches deep (onions)

Soil

Type: Well-draining loamy soil, rich in organic matter
pH: 6.0-7.5
Amendments:
Compost or aged manure (2-3 inches) Bone meal or phosphorus source Potassium sulfate Sulfur (for acidifying if needed)

Growing Zones

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Zones 3-9; garlic prefers cooler zones (3-8), onions adapt across broader range

3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b 9a 9b

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Growth Stages

1

Planting & Dormancy

4-8 weeks

Fall-planted cloves or spring onion sets establish root systems over winter or cool season. Minimal visible growth; plants appear dormant.

Plant garlic in fall (September-November); ensure adequate mulch (2-3 inches) to protect from freezing. Keep soil moist but not soggy. No fertilizing needed yet.

2

Early Growth & Emergence

4-6 weeks

Green shoots emerge in late winter/early spring. Leaves unfurl, plant develops 2-4 visible leaf blades.

Remove winter mulch gradually as temperatures warm. Begin monthly applications of balanced fertilizer (5-10-10) or fish emulsion. Ensure consistent moisture.

3

Vegetative/Leaf Development

6-10 weeks

Rapid leaf growth; plant develops 6-8+ leaves. Garlic sends up flowering scapes (in hardneck varieties). Bulbs begin sizing underground.

Remove garlic scapes when 6-8 inches tall (eat them or compost); this redirects energy to bulb. Fertilize every 2-3 weeks with nitrogen-rich formula. Maintain steady moisture.

4

Bulbing & Maturation

4-6 weeks

Leaf growth slows; cloves/layers form and enlarge underground. Lower leaves yellow and begin to brown. Plant redirects energy downward.

Reduce nitrogen, apply potassium-rich fertilizer. Taper watering as plants mature. Stop watering 2-3 weeks before harvest to cure bulbs in place.

5

Harvest & Curing

2-4 weeks curing

Tops brown and fall over (garlic); lower leaves turn papery (onions). Bulbs have protective dry outer layers.

Harvest when 50-75% of leaves have dried. Cure in warm, dry, airy location (70-80°F) for 2-4 weeks before storage. Trim tops and roots after full drying.

Companion Planting

Plan your garden →

Plant with:

Tomatoes Peppers Cabbage Broccoli Beets Carrots Lettuce Spinach Strawberries Roses Apples Raspberries

Avoid planting near:

Beans Peas Asparagus Sage Parsley Other alliums (reduce spacing; can compete)

Common Pests

  • Spray with insecticidal soap or neem oil; remove affected leaves; encourage predatory insects like ladybugs.

  • Use row covers until flowering; apply diatomaceous earth around base; crop rotation; remove infected bulbs immediately.

  • Use certified disease-free cloves; practice 3-year crop rotation; solarize soil in warm climates.

  • Use disease-resistant varieties; ensure excellent drainage; avoid overwatering; cure bulbs properly; discard infected plants.

  • Avoid planting in infested soil for 8+ years; practice strict rotation; use resistant varieties; remove and destroy infected plants.

  • Improve air circulation; avoid overhead watering; apply copper fungicide in damp conditions; remove affected leaves.

  • Use collars around transplants; apply diatomaceous earth; handpick; reduce mulch near stems.

Uses

🍳

Pesto, cooking & flavor base

Culinary

Garlic and onions are fundamental aromatics in cuisines worldwide, providing depth, umami, and pungency to soups, sauces, stir-fries, and countless dishes. [source]

💊

Immune support & cardiovascular health

Medicinal

Garlic contains allicin and sulfur compounds with antimicrobial, anti-inflammatory, and potential cholesterol-lowering properties. Traditional and modern herbalism both value garlic for immune boosting. [source]

🏠

Natural pest repellent spray

Household

Garlic or onion-based sprays (homemade or commercial) repel aphids, spider mites, whiteflies, Japanese beetles, and many other garden pests due to sulfurous compounds. [source]

🎨

Companion planting & garden biodiversity

Craft

Alliums act as natural pest barriers when interplanted with vulnerable crops, reducing need for chemical inputs and creating a more balanced garden ecosystem. [source]

🦋

Pollinator support (flowering stage)

Wildlife

Garlic scapes and onion flowers provide early-season nectar and pollen for bees, butterflies, and beneficial insects, supporting pollinator populations. [source]

This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.

Harvest Tips

Harvest garlic in late spring/early summer (May-June in northern zones) when lower leaves brown. Harvest onions when tops fall over and outer skins papery (June-August depending on region). Cure both in warm, dry, well-ventilated space for 2-4 weeks. Store in cool, dark location; properly cured garlic/onions keep 6-12+ months.

Fun Facts

  • 🌱 Garlic has been cultivated for over 5,000 years and was used by ancient Egyptians, Greeks, and Romans as both food and medicine. Workers building the pyramids were given garlic for strength and endurance.
  • 🌱 The pungent smell of garlic and onions is produced by sulfur compounds (allicin, diallyl disulfide) that form when cells are broken; this same chemistry makes them potent pest deterrents and health tonics.
  • 🌱 Hardneck garlic varieties produce ornamental flowering scapes that are edible and delicious in spring—a bonus crop before the main bulb harvest. Softneck varieties (better for mild climates) don't produce scapes.

Gardening Terms

New to gardening? Learn about terms used in this guide:

Compost Full Sun Mulch
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