Knowing when to plant sweet corn in Missouri is the first step to a successful harvest. Getting the timing right means you’ll enjoy the sweetest, fullest ears from your own backyard.
This guide will walk you through the best dates, soil tips, and simple steps for a great crop. We’ll cover everything from the last frost to picking the perfect variety for your garden.
When to Plant Sweet Corn in Missouri
For most of Missouri, the optimal planting window is from mid-April to late May. The key is soil temperature, not just the calendar.
You should plant your seeds after the danger of a hard frost has passed and when the soil has warmed up. Corn is a warm-season crop that doesn’t like cold, wet feet.
Understanding Your Missouri Planting Zone
Missouri spans USDA plant hardiness zones 5b to 7a. This means planting times can vary by a couple weeks across the state.
- Southern Missouri (Zones 6b-7a): You can often start planting in early to mid-April. The ground warms up a bit faster here.
- Central Missouri (Zones 6a-6b): Aim for late April through mid-May. This is the sweet spot for cities like Columbia and Jefferson City.
- Northern Missouri (Zones 5b-6a): Wait until early to mid-May. Frost threats linger longer in areas like Kirksville and St. Joseph.
A good general rule is to plant when soil temperatures are consistently at least 50°F (10°C). For the best germination, aim for 55-60°F. You can check this with a simple soil thermometer.
Why Soil Temperature Matters More Than Air Temperature
Corn seeds planted in cold soil are likely to rot or germinate very poorly. They just sit their and wait for warmth, vulnerable to disease and pests.
Warm soil triggers quick germination and strong seedling growth. This gives your corn a healthy head start. You can warm soil faster by using black plastic mulch a week or two before planting.
The Last Frost Date Guide
While soil temp is critical, aligning with your average last frost date is a safe practice. Here’s a quick reference:
- Southern MO: Last frost around April 10-15
- Central MO: Last frost around April 15-25
- Northern MO: Last frost around April 25 – May 5
Planting about 1-2 weeks after your area’s average last frost date is usually a safe bet. Always keep an eye on the local forcast.
How to Plant Sweet Corn for Success
Follow these steps to get your corn off to the best possible start. Proper planting technique makes a huge difference in your yield.
Step 1: Choose Your Varieties
Select types based on your taste and garden size. Consider planting a few varieties with staggered maturity dates for a longer harvest.
- Early Season (65-75 days): ‘Swift’, ‘Spring Treat’. Good for getting a early start.
- Main Season (75-85 days): ‘Bodacious’, ‘Kandy Korn’. Excellent, reliable sweetness.
- Late Season (85-95 days): ‘Argent’, ‘Peaches and Cream’. For planting later in the season.
Remember, sweet corn is pollinated by wind. Plant in blocks of at least 4 rows rather than one long row for good kernel development.
Step 2: Prepare the Soil
Corn needs rich, well-drained soil. Work in 2-3 inches of compost or well-rotted manure before planting.
It’s also a heavy feeder. You can mix in a balanced organic fertilizer according to package directions. A soil test from your local extension office is the best way to know what your soil needs.
Step 3: Planting the Seeds
- Plant seeds 1 to 1.5 inches deep.
- Space seeds about 9-12 inches apart within the row.
- Space rows 30-36 inches apart. This gives plants room to grow and allows for easy weeding.
- Water the seeds in well after planting to ensure good soil contact.
For a continuous harvest, plant a new block every 10-14 days until early summer. Just make sure your last planting has enough time to mature before fall frost.
Caring for Your Sweet Corn Crop
Consistent care after planting ensures healthy stalks and full ears. The main tasks are watering, weeding, and feeding.
Watering Requirements
Corn needs about 1 inch of water per week, more during hot, dry spells or when the tassels and ears are forming. Water deeply at the soil level, not with a light sprinkling from above.
Drought stress during pollination is a common cause of poorly filled ears. Using a soaker hose or drip irrigation is a great way to deliver water efficently.
Weeding and Fertilizing
Keep the area around your corn free of weeds, especially when plants are young. Weeds compete heavily for water and nutrients.
When corn is about knee-high (12 inches tall), side-dress it with a nitrogen-rich fertilizer. This gives it a boost for the rapid growth stage ahead. Simply scratch the fertilizer into the soil along the sides of the rows and water it in.
Common Pests and Problems
Watch out for a few typical issues:
- Corn Earworm: A caterpillar that feeds on the tips of ears. An organic control is to put a few drops of mineral oil on the silk just as it starts to brown.
- Raccoons & Birds: They love ripe corn. Some gardeners find motion-activated lights or sprinklers helpful, or they harvest just as the corn ripens.
- Poor Pollination: Leads to ears with missing kernels. Always plant in blocks, not single rows, to ensure the wind can move pollen from the tassels to the silks.
Harvesting Your Missouri Sweet Corn
Your corn is ready about 18-24 days after the first silks appear. The silks will be brown and dry, and the ears will feel plump.
Peel back a small part of the husk and poke a kernel with your fingernail. If the liquid inside is milky, it’s perfect. If it’s clear, it’s not ready. If it’s thick, you’ve waited to long.
For the best flavor, harvest in the morning and get the ears into cool water or your cooking pot immediately. The sugars in sweet corn begin converting to starch as soon as its picked.
Frequently Asked Questions
Can I plant sweet corn in early April in Missouri?
In southern Missouri, early April is sometimes possible if soil is warm. In central and northern Missouri, it’s usually to risky due to cold soil and late frosts. Mid to late April is safer.
What is the latest I can plant sweet corn?
You can plant until early July in most areas, but you must choose an early-maturing variety (65-75 days). Count back from your average first fall frost to ensure it has time to mature.
How do I check my soil temperature?
Use a soil thermometer. Insert it 4 inches deep in the area you plan to plant, preferably in the morning. Check for several consecutive days to get a consistent reading.
Why did my corn not produce full ears?
This is most often due to poor pollination. Remember to plant in blocks of short rows, not one or two long rows. Also, avoid planting during very hot, dry weather which can dessicate the silks.
Can I grow sweet corn in a small garden?
Yes. Choose a space that gets full sun and plant in a block (e.g., 4 plants by 4 plants) instead of rows. Some shorter varieties are also bred for small spaces. Hand pollination can help if you only have a few plants.
Following this guide for when to plant sweet corn in Missouri will set you up for a rewarding season. With the right timing, a little soil preparation, and consistant care, you’ll be enjoying the incredible taste of homegrown sweet corn all summer long. There’s nothing quite like it.