Planting onions and garlic together in the fall creates a harmonious cycle of harvests that stretches from late spring into summer. Knowing exactly when to plant onions and garlic is the key to unlocking a bountiful garden, but timing depends heavily on your climate and the specific varieties you choose. This guide will walk you through everything you need to know, from soil preparation to harvest signals, so you can grow these kitchen staples with confidence.
Onions and garlic are both cool-season crops, but they have different growth habits and planting windows. Garlic is almost always planted in the fall, while onions can be planted in either fall or spring, depending on your region. Understanding these nuances will help you maximize your yield and avoid common mistakes.
Let’s start with the basics. Onions are day-length sensitive, meaning they bulb based on how many hours of daylight they receive. Garlic, on the other hand, requires a period of cold vernalization to form large, healthy bulbs. This is why fall planting is so important for garlic in most climates.
When To Plant Onions And Garlic
The best time to plant onions and garlic is determined by your hardiness zone and the specific type you’re growing. For garlic, aim for 4–6 weeks before the ground freezes solid. This gives the cloves time to establish roots without sending up top growth. For onions, you have two main options: fall planting for overwintering varieties or spring planting for traditional bulbs.
In general, gardeners in zones 3–6 should plant garlic in late September to October. In zones 7–9, you can plant garlic from October through December. Onions for spring harvest should be planted as soon as the soil is workable in early spring, while overwintering onions are planted in late summer or early fall.
Here’s a simple rule of thumb: if your winters are harsh, plant garlic in the fall and onions in the spring. If your winters are mild, you can plant both in the fall for an earlier harvest. The key is to avoid planting too early, which can lead to disease, or too late, which can result in poor root development.
Understanding Your Growing Zone
Your hardiness zone is the single most important factor in determining planting dates. Use the USDA zone map to find your zone, then adjust based on local weather patterns. For example, a gardener in zone 5 might plant garlic in mid-October, while someone in zone 8 might wait until November.
Onions are more flexible. Short-day onions are best for southern zones (7–10), while long-day onions thrive in northern zones (3–6). Intermediate-day onions work well in zones 5–7. This day-length sensitivity means you can’t just plant any onion variety anywhere.
- Garlic planting window: 4–6 weeks before first hard frost
- Onion planting window (spring): 2–4 weeks before last frost
- Onion planting window (fall): 6–8 weeks before first frost
Soil Preparation For Onions And Garlic
Both crops prefer loose, well-draining soil rich in organic matter. Test your soil pH and aim for 6.0–7.0. Add compost or aged manure a few weeks before planting to give your bulbs a nutrient boost. Avoid fresh manure, which can burn roots and introduce pathogens.
Onions and garlic are heavy feeders, so incorporate a balanced fertilizer (10-10-10) into the top 6 inches of soil. Work the soil deeply to remove rocks and clods that can deform bulbs. Raised beds are ideal for heavy clay soils.
Step-by-Step Soil Prep
- Clear the area of weeds and debris.
- Loosen soil to a depth of 8–10 inches.
- Mix in 2–3 inches of compost.
- Add fertilizer according to package directions.
- Rake the bed smooth and water lightly.
Planting Garlic Cloves
Break apart garlic bulbs into individual cloves just before planting. Choose the largest cloves for the biggest bulbs. Plant each clove 2 inches deep, with the pointed end facing up. Space cloves 6 inches apart in rows 12 inches apart. Cover with soil and water in well.
Mulch heavily with straw or leaves after planting to insulate the soil and suppress weeds. In cold climates, a 4–6 inch layer of mulch is essential for winter survival. Remove the mulch in spring once growth begins.
Garlic varieties fall into two main types: hardneck and softneck. Hardneck garlic produces a flower stalk (scape) and has larger, more flavorful cloves. Softneck garlic stores longer and is better for braiding. Choose based on your climate and storage needs.
Planting Onion Sets Or Seeds
Onions can be grown from seeds, sets (small bulbs), or transplants. Sets are easiest for beginners and produce quicker harvests. Plant sets 1 inch deep, with the tip just above the soil surface. Space sets 4–6 inches apart in rows 12–18 inches apart.
If starting from seed, sow indoors 8–10 weeks before your last frost date. Harden off seedlings before transplanting outdoors. Onion seeds are slow to germinate, so be patient and keep the soil consistently moist.
For fall-planted onions, choose overwintering varieties like ‘Walla Walla’ or ‘Egyptian Walking Onion’. Plant them in late summer to establish roots before winter. They will resume growth in spring and mature earlier than spring-planted onions.
Watering And Fertilizing
Onions and garlic need consistent moisture, especially during bulb formation. Water deeply once a week, providing about 1 inch of water. Reduce watering as the bulbs mature to prevent rot. Overwatering can lead to fungal diseases.
Fertilize every 3–4 weeks during the growing season with a nitrogen-rich fertilizer. Stop fertilizing once the bulbs start to swell. Too much nitrogen late in the season can cause lush tops but small bulbs.
Common Pests And Diseases
Onion thrips, onion maggots, and garlic mites are common pests. Use row covers to protect young plants, and rotate crops to break pest cycles. Companion planting with carrots or marigolds can help deter pests.
Diseases like white rot, downy mildew, and botrytis can affect both crops. Practice good garden hygiene by removing infected plants and avoiding overhead watering. Plant disease-resistant varieties when possible.
Harvesting Onions And Garlic
Garlic is ready to harvest when the lower leaves turn brown but the upper leaves are still green. This usually occurs in mid-summer, about 8–10 months after fall planting. Dig carefully to avoid bruising the bulbs.
Onions are ready when the tops fall over and begin to yellow. Stop watering once the tops flop, then wait a week before harvesting. Pull onions on a dry day and cure them in a warm, airy place for 2–3 weeks.
Signs of Readiness
- Garlic: 3–4 green leaves remain; bulbs are firm and well-formed.
- Onions: Tops are 50–75% fallen over; necks are soft.
Curing And Storing
Curing is essential for long-term storage. Hang garlic in bunches or lay onions on a screen in a shaded, well-ventilated area. Allow the outer skins to dry and the necks to tighten. This process takes 2–4 weeks.
Store cured bulbs in a cool, dark place with good air circulation. Ideal temperatures are 32–40°F for garlic and 32–45°F for onions. Avoid storing onions with potatoes, as they can cause each other to spoil.
Fall Planting Vs. Spring Planting
Fall planting gives garlic and overwintering onions a head start, leading to larger bulbs and earlier harvests. Spring planting is safer for northern gardeners with harsh winters. Both methods work, but fall planting often produces better yields.
Consider your garden’s microclimate. If you have heavy clay soil that stays wet in spring, fall planting might be risky due to rot. In sandy soil, fall planting is usually fine. Experiment with both to see what works best in your garden.
Tips For Success
- Rotate crops every 3–4 years to prevent soilborne diseases.
- Use raised beds for better drainage in wet climates.
- Plant garlic and onions in full sun for best growth.
- Remove flower stalks from hardneck garlic to focus energy on bulbs.
- Mulch to conserve moisture and suppress weeds.
Frequently Asked Questions
Can I Plant Onions And Garlic Together In The Same Bed?
Yes, you can plant them together, but keep them spaced apart to avoid competition. Onions and garlic have similar needs, so they grow well as companions. Just ensure both have enough room to develop.
What Happens If I Plant Garlic Too Late?
Late-planted garlic may not develop a strong root system before winter, leading to smaller bulbs or winter kill. Aim for 4–6 weeks before the ground freezes to give roots time to establish.
Do I Need To Water Onions And Garlic In Winter?
No, winter watering is not necessary if you get regular rainfall. In dry climates, water once after planting to settle the soil, then let nature take over. Overwatering in winter can cause rot.
Can I Grow Onions From Grocery Store Onions?
It’s possible, but not recommended. Grocery store onions may carry diseases or be treated to prevent sprouting. Use certified seed or sets from a reputable supplier for best results.
How Deep Should I Plant Garlic Cloves?
Plant garlic cloves 2 inches deep, with the pointed end up. In cold climates, you can plant slightly deeper (3 inches) for extra insulation. Shallow planting can lead to frost heaving.
With these guidelines, you’re ready to plant onions and garlic with confidence. Remember that timing is everything, but don’t stress if your dates aren’t perfect. Gardening is a learning process, and each season teaches you something new. Start with a small patch, observe your plants, and adjust next year. Your kitchen will thank you when you’re pulling fresh bulbs from the garden.