When To Plant Onions In North Carolina

If you’re a gardener in North Carolina, knowing when to plant onions is the first step to a great harvest. Getting the timing right is crucial because onions are sensitive to day length and temperature. This guide will walk you through the optimal timing for planting onions in North Carolina, tailored to our unique climate.

Planting at the correct time ensures your onions have enough time to grow large bulbs before the summer heat triggers them to start maturing. A mistimed planting can lead to small bulbs or plants that bolt (flower) prematurely. Let’s break down the schedule so you can plan your garden perfectly.

In North Carolina, onions are primarily planted in two seasons: fall and late winter. The best time for you depends on your location within the state and the type of onion you choose.

For most of North Carolina, the optimal window for planting onion sets or transplants is from late February through mid-March. In the warmer coastal plain and piedmont, you can start as early as late February. In the cooler mountain regions, aim for mid to late March.

For a fall planting, which is excellent for producing early green onions or overwintering bulb onions, plant sets or seeds in October. This method works well in the piedmont and coastal areas.

Understanding Onion Types: Short-Day vs. Long-Day

This is the most important concept for southern growers. Onions form bulbs based on day length.

Short-Day Onions: These bulb up when daylength reaches 10-12 hours. They are perfect for North Carolina’s southern latitude. Plant them in late winter.
Intermediate-Day (Day-Neutral) Onions: These bulb with 12-14 hours of daylight. They are very reliable and adaptable across the entire state.
Long-Day Onions: Need 14-16 hours of daylight to bulb, which North Carolina summer days don’t provide. Avoid these, as they will likely not form good bulbs here.

Stick with short-day or intermediate-day varieties for success. Popular choices include Texas Sweet, Candy (intermediate), Red Burgundy, and Southern Belle.

Breaking Down the Planting Calendar by Region

North Carolina has three distinct growing regions. Your planting dates should align with your local conditions.

Coastal Plain Region

This region has mild winters and early springs. You have the longest growing window.

Spring Planting: Plant onion sets or transplants between February 20th and March 10th.
Fall Planting: For a fall crop, sow seeds or sets around October 15th.

Piedmont Region

The piedmont is the central part of the state, with moderate winters. It’s the standard for timing.

Spring Planting: The ideal time is from March 1st to March 20th.
Fall Planting: Aim for planting around October 25th for overwintering.

Mountain Region

Cooler temperatures and later springs mean a shifted schedule. Frosts can occur late into spring.

Spring Planting: Wait until late March, ideally between March 25th and April 10th.
Fall Planting: This is less common due to harsh winters, but if attempted, plant by early October.

Step-by-Step Guide to Planting Your Onions

Once you’ve got your timing down, follow these steps for a healthy crop.

1. Choosing Your Planting Material

You can start onions from seeds, sets (small bulbs), or transplants (seedlings).

Seeds: Most economical, but require starting indoors 8-10 weeks before planting out. Offers the most variety.
Sets: Easiest for beginners. These are small, dormant onion bulbs. Look for ones no larger than a dime to avoid bolting.
Transplants: These are young plants from a nursery. They give you a head start and are widely available at local garden centers in late winter.

2. Preparing Your Soil

Onions need loose, well-draining soil rich in organic matter. They are heavy feeders.

Choose a site with full sun (at least 6-8 hours daily).
Work the soil to a depth of 8 inches, removing any rocks or clumps.
Mix in 2-3 inches of compost or well-rotted manure. Add a balanced, slow-release fertilizer according to package directions.
Raised beds are an excellent option, especially if you’re garden soil is heavy clay.

3. The Planting Process

For Sets & Transplants: Plant them about 1 inch deep. Space sets/transplants 4-6 inches apart in rows that are 12-18 inches apart. The neck (where the leaves meet the roots) should be just at or below the soil surface.
For Seeds (direct sown): Sow seeds ½ inch deep and 1 inch apart. Later, you’ll thin the seedlings to the proper 4-inch spacing.
Water the bed thoroughly after planting to settle the soil.

Caring for Your Growing Onions

Consistent care is key to plump, healthy bulbs. Onions have shallow roots systems, so they need regular attention.

Watering and Weeding

Onions need about 1 inch of water per week. Water deeply when the top inch of soil feels dry. Drip irrigation or a soaker hose is best to keep foliage dry and prevent disease.

Weeds compete fiercely with onions. Mulch lightly with straw or shredded leaves to supress weeds and retain moisture. Hand-pull any weeds that do appear carefully to avoid disturbing the onion roots.

Fertilizing for Success

Feed your onions every 2-3 weeks with a nitrogen-rich fertilizer, like fish emulsion or a synthetic 21-0-0 blend, until the bulbs begin to swell. Stop fertilizing once the bulbs start to form, as too much nitrogen then can hurt storage quality.

Knowing When to Harvest

Harvest time typically comes in early to mid-summer, about 90-110 days after planting transplants.

Green Onions: You can harvest these anytime they reach a usable size.
Bulb Onions: Watch for the signal: the tops will turn yellow and begin to fall over naturally.

Once tops have fallen, stop watering. Gently lift the bulbs with a fork after a week. Let them cure (dry) in a warm, airy, shaded place for 2-3 weeks until the necks are tight and the outer skins are papery. Then, you can store them.

Common Problems and Solutions in NC

Our humid climate can pose some challenges. Keep an eye out for these issues.

Bolting: When an onion sends up a flower stalk. Caused by temperature fluctuations or planting too large of sets. Choose the right variety and small sets. If one bolts, harvest and use it immediately.
Pests: Thrips are tiny insects that cause silvery streaks. Use insecticidal soap or neem oil. Onion maggots are less common but can be deterred with crop rotation.
Diseases: Fungal issues like downy mildew or botrytis can occur in wet weather. Ensure good air circulation, avoid overhead watering, and rotate where you plant onions each year.

FAQ: Planting Onions in North Carolina

Can I plant onions in the fall in NC?

Yes, you can. Planting in October with sets or transplants can yield an early summer harvest or provide green onions through the winter in milder areas. Use hardy, short-day varieties.

What is the best onion variety for North Carolina?

Stick with short-day or intermediate-day types. Excellent choices include ‘Texas 1015Y Supersweet’, ‘Candy’ (an intermediate hybrid), ‘Red Creole’, and ‘Granex’ (the famous Vidalia type).

How deep should I plant onion sets?

Plant onion sets so the tip is just barely showing above the soil, or cover them with about 1 inch of soil. Planting them to deep can hinder bulb development.

Can I grow onions from grocery store scraps?

You can regrow the green tops from a scallion or onion bottom in water for fresh greens, but this won’t produce a new, full-sized bulb. For bulb onions, it’s best to start with seeds, sets, or transplants meant for gardening.

Why are my onion bulbs so small?

Small bulbs are often caused by planting at the wrong time (too late), using the wrong day-length variety, overcrowding, or insufficent water and nutrients during the growing season. Double-check your planting schedule and variety choice.

By following this schedule and tips, you’ll be well on your way to harvesting a bounty of homegrown onions. Remember, the key is matching the right onion type with the right planting window for your specific part of North Carolina. With a little planning, you can enjoy this garden staple straight from your own backyard.