When To Plant Onions In Indiana

Getting your onion planting timing right in Indiana is the single biggest factor for a succesful harvest. If you’re wondering when to plant onions in Indiana, the answer depends on the type of onion and how you start them. This guide will walk you through the optimal timing for planting, along with all the tips you need for a bumper crop.

Onions are a cool-season crop, which means they prefer to start their life in cooler spring soil and mature as the days get longer and warmer. Planting at the correct time allows them to establish strong roots and foliage before focusing on bulb development. Planting too late often results in disappointingly small bulbs.

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

This is the most important concept for Indiana gardeners. Onions form bulbs based on day length, not just age.

Long-Day Onions: These require 14-16 hours of daylight to trigger bulbing. They are perfectly suited for northern states like Indiana. Plant these.
Short-Day Onions: These bulb with only 10-12 hours of daylight and are best for southern states. They will bulb too early in Indiana’s spring, producing small onions.
Day-Neutral (Intermediate-Day) Onions: A flexible type that bulbs with 12-14 hours of daylight. They can work well in Indiana, especially in central and southern parts, offering more variety options.

Optimal Planting Dates by Method

You can start onions from seeds, sets (small bulbs), or transplants (seedlings). Each has its own ideal schedule.

Planting Onion Seeds Indoors

For the widest variety, start seeds indoors. This gives them a long head start.

Start seeds 10-12 weeks before your last expected spring frost.
In Northern Indiana (frost date ~May 10), start seeds around mid-February.
In Central Indiana (frost date ~April 25), start seeds in early February.
In Southern Indiana (frost date ~April 15), start seeds in late January.

Transplant the sturdy seedlings into the garden 4-6 weeks before your last frost date, once the soil is workable.

Planting Onion Sets or Transplants

This is the easiest and most common method for home gardeners.

Onion Sets: These are small, dormant onion bulbs. Plant them in the garden as soon as the soil can be worked in early spring, typically late March to mid-April across Indiana. They can tolerate a light frost.
Purchased Transplants: These are bundles of live seedlings. Get them in the ground at the same time as sets, from late March to mid-April.

Fall Planting for a Head Start

Ambitious gardeners can plant a fall crop of certain onions. The goal is not to harvest in fall, but to get established for a very early spring harvest.

Plant onion sets in late September to mid-October.
Choose varieties specifically marketed for overwintering.
Mulch heavily with straw after the ground freezes to prevent heaving.
They will resume growth very early in spring, giving you green onions or early bulbs.

Step-by-Step Planting Guide

Once your timing is right, follow these steps for sucess.

1. Choose the Right Variety

Stick with long-day or day-neutral varieties. Some excellent choices for Indiana include:

Yellow: Patterson, Copra, Yellow Sweet Spanish
Red: Redwing, Red Zeppelin
White: White Sweet Spanish, Sterling

2. Prepare Your Soil

Onions need loose, well-draining soil with plenty of nutrients.

Choose a site with full sun (at least 6-8 hours).
Work the soil to a depth of 8-10 inches, removing rocks and clumps.
Mix in 2-3 inches of compost or well-rotted manure. Onions are heavy feeders.
A soil test is ideal; they prefer a pH between 6.0 and 6.8.

3. Planting Correctly

For sets and transplants, space plants 4-6 inches apart in rows 12-18 inches apart.
Plant onion sets just deep enough so the tip is level with the soil surface. Don’t bury them to deep.
Plant transplants at the same depth they were growing in their cell pack.
Water thoroughly after planting to settle the soil.

Caring for Your Onion Crop

Consistent care through the season is key to large, firm bulbs.

Watering and Weeding

Onions have shallow roots and need consistent moisture, especially during bulb formation.

Water deeply when the top inch of soil feels dry, providing about 1 inch per week.
Use drip irrigation or water at the base to keep foliage dry and prevent disease.
Weed meticulously, as onions don’t compete well. A light mulch of straw can help suppress weeds and retain moisture.

Fertilizing for Success

Feed your onions to support their long growing season.

At planting, use a balanced fertilizer or one slightly higher in phosphorus.
Side-dress with a nitrogen-rich fertilizer (like blood meal) every 3-4 weeks until bulbs begin to form.
Stop fertilizing once the bulbs start to swell, as excess nitrogen then can hurt storage quality.

Knowing When to Harvest

Harvest time depends on whether you want green onions or storage bulbs.

Green Onions (Scallions): You can harvest these at any stage once the tops are about 6 inches tall. Simply pull as needed.
Bulb Onions: They are ready when the tops naturally fall over and begin to turn yellow and brown. This usually happens in mid-to-late summer.

Once tops have fallen, stop watering. After about a week, gently lift the bulbs with a fork on a dry, sunny day.

Curing and Storing Your Harvest

Proper curing is essential for onions that will last.

Lay bulbs in a single layer in a warm, dry, well-ventilated place out of direct sun. A garage or covered porch works well.
Let them cure for 2-3 weeks until the necks are tight and dry and the outer skins are papery.
Trim roots and cut tops back to about 1 inch.
Store in a cool, dry, dark place in mesh bags or a single layer in a box. Check periodically for soft onions.

Common Problems and Solutions

Watch out for these typical onion issues.

Small Bulbs: Usually caused by late planting, incorrect onion type (short-day), or overcrowding.
Bolting (Flowering): When an onion sends up a flower stalk, the bulb stops growing. This is often triggered by temperature fluctuations. Use sets less than 3/4 inch in diameter, as larger sets are more prone to bolt.
Pests: Onion thrips and onion maggots are the main culprits. Use row covers to prevent maggot flies, and spray a strong stream of water for thrips.
Diseases: Good air circulation, crop rotation (don’t plant onions in the same spot for 3 years), and avoiding overhead watering prevent most fungal issues like downy mildew.

FAQ: Planting Onions in Indiana

What is the latest you can plant onions in Indiana?

For bulb onions, you should get sets or transplants in the ground by early May at the absolute latest. Planting after this significantly reduces bulb size due to the shorter growing period before summer heat.

Can I plant onions in the same bed as last year?

It’s not recommended. Rotating your onion family crops (onions, garlic, leeks) helps prevent a buildup of soil-borne diseases and pests. Wait at least 2-3 years before replanting onions in the same spot.

How do I know if I bought the right type of onion for Indiana?

Always check the seed packet or plant tag. It should clearly state “Long-Day” or “Day-Neutral/Intermediate-Day.” If it says “Short-Day,” save it for a container experiment or use it exclusively for early green onions.

Do onions need a lot of sun?

Yes, they require full sun to develop properly. Aim for a minimum of 6 hours of direct sunlight, but 8 or more is ideal for good bulb formation.

Why are my onion tops turning yellow?

A little yellowing at the neck as bulbs mature is normal. Widespread yellowing earlier in the season could indicate overwatering, poor drainage, nitrogen deficiency, or a pest like onion thrips. Assess your watering and check the undersides of leaves for tiny insects.

By following this timing guide and care tips, you’ll be well on your way to harvesting a plentiful supply of homegrown onions. The sweet, crisp flavor of an onion you grew yourself is worth the wait. Just remember the golden rules: choose long-day varieties and get them in the ground early as soon as the spring soil is ready.