When Do You Plant Onions In Michigan

If you’re planning your Michigan garden, knowing when do you plant onions in Michigan is the first step to a great harvest. Getting the timing right is crucial for those big, flavorful bulbs. Our springs can be unpredictable, but onions are tough once they get started. This guide will walk you through the best dates, varieties, and methods for success.

Onions are a cool-season crop, which means they thrive in the cooler temperatures of spring and fall. In Michigan, we can grow them from seeds, sets (small bulbs), or transplants. Each has it’s pros and cons. The goal is to get them in the ground early so they can grow lots of leaves before the long, warm days of summer trigger bulb formation.

For a spring harvest, the planting window in Michigan is generally from late March to early May. The exact date depends heavily on your location and the weather in a given year. The key is soil temperature and workability, not just the calendar.

You can plant as soon as the ground can be worked in the spring. This means the soil is no longer frozen and has dried out enough that it doesn’t clump when you dig. For most of Lower Michigan, this is often in early to mid-April. For the Upper Peninsula and colder areas, aim for late April or early May.

Understanding Your Michigan Growing Zone

Michigan spans USDA plant hardiness zones 4 through 6. This affects your precise timing:

Zones 6a & 6b (Southeast & Lake Michigan coast): You can often plant earliest, sometimes in late March or the first week of April if conditions allow.
Zones 5a & 5b (Most of Lower Michigan): Target mid-April. This includes cities like Lansing, Grand Rapids, and Flint.
Zone 4 (Northern Lower & UP): Plan for late April or early May. Wait for the soil to warm up a bit.

A simple rule is to plant onions around the same time you plant peas or lettuce. If you’re unsure, a soil thermometer is a great tool. Onion seeds will germinate in soil as cool as 35°F, but 50°F is ideal for faster growth.

Choosing Your Onion Type: Day Length is Key

This is the most important factor many gardeners miss. Onions form bulbs based on day length, and choosing the wrong type for our latitude leads to disappointment.

Long-Day Onions: These need 14-16 hours of daylight to form bulbs. They are perfect for Michigan and northern states. Plant these for your main spring harvest.
Short-Day Onions: These bulb up with only 10-12 hours of daylight. They’re suited for southern states and will not perform well here.
Day-Neutral (Intermediate-Day) Onions: These are flexible and form bulbs with 12-14 hours of daylight. They can also work well in Michigan and are often good for storage.

Always check the seed packet or plant tag to ensure you’re getting a long-day or day-neutral variety.

Recommended Onion Varieties for Michigan

Stick with proven performers. Here are some excellent long-day and day-neutral choices:

Yellow Storage: Patterson, Copra, Yellow Sweet Spanish
Red: Redwing, Red Zeppelin
White: White Sweet Spanish, Sterling
Sweet (best used fresh): Walla Walla (a day-neutral that does well here), Ailsa Craig

How to Plant Onions in Michigan Soil

Onions need loose, well-draining soil with plenty of organic matter. They are heavy feeders, especially on nitrogen early on. Follow these steps:

Step 1: Prepare the Bed

Choose a spot with full sun. Work the soil to a depth of about 8 inches, removing rocks and weeds. Mix in 2-3 inches of compost or well-rotted manure. You can also add a balanced fertilizer according to package directions.

Step 2: Planting Seeds, Sets, or Transplants

From Seed (started indoors): Start seeds indoors 10-12 weeks before your outdoor planting date. This gives you the widest variety choice. Harden off seedlings before transplanting.

From Sets: This is the easiest method. Select sets that are firm and about 3/4 inch in diameter. Larger sets can sometimes bolt (flower) too early.

From Transplants: These are young plants, often sold in bunches. They give you a head start and are a great option.

Step 3: Spacing and Depth

Seeds: Sow 1/4 inch deep, thin seedlings to 4 inches apart.
Sets & Transplants: Plant so the tip is just at the soil surface. Space them 4-6 inches apart in rows that are 12-18 inches apart. Don’t bury them to deep.

Caring for Your Growing Onions

Consistent care is simple but vital for good bulb development.

Watering: Onions have shallow roots. Provide about 1 inch of water per week, including rainfall. Keep the soil consistently moist but not soggy. Reduce watering as the bulbs mature and the tops begin to fall over.
Weeding: Weed carefully by hand. Onions don’t compete well with weeds, which can steal nutrients and water.
Fertilizing: Feed every few weeks with a nitrogen-rich fertilizer until bulbs begin to form. Then, stop fertilizing.
Mulching: A light layer of straw or grass clippings helps retain moisture, suppress weeds, and keep soil temperatures even.

Common Pests and Problems in Michigan

Onions are relatively pest-free, but a few issues can pop up:

Onion Maggots: The most common pest. The larvae feed on the roots and bulbs. Use floating row covers to prevent the fly from laying eggs. Rotate your onion family crops (garlic, leeks) each year.
Thrips: Tiny insects that cause silvery streaks on leaves. A strong spray of water or insecticidal soap can help manage them.
Bolting: When an onion sends up a flower stalk. The bulb stops growing and won’t store well. It’s often caused by temperature fluctuations. Use the right-sized sets and choose bolt-resistant varieties.
Rot: Caused by to much moisture in the soil. Ensure good drainage and avoid overwatering.

Harvesting and Curing for Storage

Your onions are ready when the tops turn yellow and begin to fall over. This usually happens in late July or August.

Gently lift the bulbs from the soil with a fork on a dry day.
Lay them out in a single layer in a warm, dry, airy place out of direct sun. A garage, covered porch, or well-ventilated shed is perfect.
Let them cure for 2-3 weeks until the necks are tight and dry and the outer skins are papery.
Trim the roots and cut the tops down to about 1 inch, unless you plan to braid them.
Store in a cool, dry, dark place in mesh bags or baskets. Properly cured long-day onions can store for many months.

FAQ: Planting Onions in Michigan

Can I plant onions in the fall in Michigan?

Yes, but for a different purpose. Fall-planted onions (using sets) are typically grown for early spring green onions or scallions. They rarely form large bulbs because they will bolt when days lengthen the following summer. For storage bulbs, spring planting is best.

What is the latest I can plant onions in spring?

You can plant into early May, but later planting means smaller bulbs. The plant needs enough time to grow green tops before the summer solstice triggers bulbing. After June, it’s to late for a good bulb harvest.

Why are my onion bulbs so small?

Small bulbs are usually caused by late planting, incorrect day-length variety (like using a short-day onion), overcrowding, insufficient water during growth, or poor soil fertility. Ensure you meet all the basic requirements listed above.

Can I grow onions in containers?

Absolutely. Choose a container at least 10 inches deep. Use a quality potting mix and ensure it has excellent drainage. Water more frequently, as containers dry out faster. Follow the same spacing and care guidelines.

Should I bend the onion tops over at harvest?

No, you shouldn’t force them. Let the tops fall over naturally. This is a sign the onion has stopped growing and is ready to begin the curing process. Bending them prematurely can damage the neck and lead to rot during storage.

With the right timing and care, growing onions in Michigan is very rewarding. By planting at the correct time in spring, choosing long-day varieties, and providing simple consistent care, you’ll be set for a successful harvest of homegrown onions that will last you through the winter.