When To Plant Potatoes In Illinois

If you’re planning your garden in Illinois, knowing when to plant potatoes is your first step to a great harvest. Getting the timing right makes all the difference for a healthy crop.

Potatoes are a cool-season vegetable, which means they like to start in cool soil. Planting too early risks frost damage to the sprouts. Planting too late exposes the plants to our hot Illinois summers too soon, which can halt tuber growth. The key is to watch the weather, not just the calendar.

For most of Illinois, the optimal planting window is from late March to mid-April. This targets the period a few weeks before your last expected spring frost. The soil temperature is the best guide—it should be consistently at least 45°F (7°C). You can check this with a simple soil thermometer.

Illinois has a big range in climate from north to south. This means planting dates shift significantly depending on where you live.

Northern Illinois (Zones 5a-5b)

This includes areas like Chicago, Rockford, and Galena. Springs are cooler and last frosts come later.

Optimal Planting Time: Early to late April.
Last Frost Date: Typically around May 15th.
Tip: Wait for soil to dry out a bit from spring snowmelt and rain. Wet, cold soil will cause seed potatoes to rot.

Central Illinois (Zones 5b-6a)

This covers cities like Springfield, Peoria, and Bloomington. This region has a bit more flexibility.

Optimal Planting Time: Late March to mid-April.
Last Frost Date: Typically around April 15th to April 30th.
Tip: This is the most common timing for the state. Gardeners here often have great success with St. Patrick’s Day as a traditional starting point to prepare.

Southern Illinois (Zones 6a-6b)

This includes Carbondale, Mt. Vernon, and Cairo. Winters are milder and springs warm up faster.

Optimal Planting Time: Mid-March to early April.
Last Frost Date: Typically around April 7th to April 15th.
Tip: You can plant earliest here, but be prepared to hill soil or use straw to protect early foliage from a surprise late frost.

How to Prepare Seed Potatoes

You don’t plant potatoes from the grocery store. You use “seed potatoes” certified disease-free from a garden center. Here’s how to get them ready, a process called chitting.

Buy your seed potatoes 2-3 weeks before your planting date.
Place them in a cool, bright spot (like a windowsill) with the “eyes” facing up. The eyes are the little dimples where sprouts grow from.
Small, sturdy green sprouts about ½-inch to 1-inch long will form. This gives them a head start.
One or two days before planting, cut larger seed potatoes into pieces. Each piece should be about the size of a golf ball and must have at least 2-3 strong eyes.
Let the cut pieces sit out so the cut surfaces dry and form a callus. This prevents rot in the ground.

Step-by-Step Planting Guide

Follow these steps for a successful planting day.

Choose a Sunny Spot: Potatoes need full sun—at least 6 hours of direct sunlight daily.
Prepare the Soil: They prefer loose, well-draining soil rich in organic matter. Work in some compost or aged manure. Avoid fresh manure, as it can cause scab disease on the tubers.
Dig Trenches or Holes: Dig trenches about 6 inches deep and 3 feet apart. You can also use individual holes for each seed piece.
Plant the Seeds: Place the seed potato pieces cut-side down, with the eyes pointing up. Space them about 12 inches apart in the trench.
Cover Gently: Cover with 4 inches of soil. Leave the remaining 2 inches of trench depth empty for later.
Water Lightly: Give them a good initial watering to settle the soil, but don’t soak it.

Caring for Your Potato Plants

Proper care after planting is simple but crucial.

Hilling

This is the most important task. When the green plants are about 6-8 inches tall, gently mound soil from around the plant up around the stems, leaving just the top few leaves exposed. Repeat this process every few weeks. Hilling protects developing tubers from sunlight (which turns them green and toxic), supports the plant, and increases your yield.

Watering

Potatoes need consistent moisture, especially once they start forming tubers. Aim for about 1-2 inches of water per week. Water deeply at the base of the plants. Try to keep the foliage dry to prevent disease. Inconsistent watering leads to knobby or cracked potatoes.

Fertilizing

Mix a balanced, slow-release fertilizer into the soil at planting. When plants are about halfway through their growth, you can side-dress with a low-nitrogen fertilizer. Too much nitrogen early on gives you lots of leaves but few potatoes.

When to Harvest in Illinois

Harvest times depend on the potato type and what you want.

New Potatoes: For small, tender “new” potatoes, you can carefully dig around the plant about 7-8 weeks after planting, just after flowering.
Mature Potatoes (for storage): Wait until the plant vines have completely yellowed and died back, usually in late July or August. Stop watering at this point. Dig carefully on a dry day, let them cure in a cool, dark place for 1-2 weeks, then store.

Common Problems and Solutions

Green Potatoes: Caused by tubers exposed to light. Hill your plants more thoroughly and store harvested potatoes in complete darkness.
Colorado Potato Beetle: Hand-pick the orange larvae and adults off plants. Row covers can also help.
Early/Late Blight: These are fungal diseases. Ensure good air circulation, water at the soil level, and rotate your potato crop to a new spot each year.

FAQ

Can I plant potatoes in the fall in Illinois?
Generally, no. Our winters are too cold for potatoes to survive in the ground. Spring planting is recommended for almost all gardeners.

What is the best potato variety for Illinois?
Early varieties like ‘Yukon Gold’ and ‘Red Norland’ do well to avoid the peak summer heat. Mid-season varieties like ‘Kennebec’ are also very reliable for a main crop.

How late is too late to plant potatoes?
If you plant after mid-May, the plants will hit tuber formation during the hottest part of summer. This stresses the plant and greatly reduces yield. Aim for that spring window.

Can I use store-bought potatoes to plant?
It’s not advised. They are often treated with sprout inhibitors and may carry disease that can persist in your soil for years. Certified seed potatoes are a safer investment.

Do potatoes need a lot of space?
They do need some room for hilling. If space is limited, you can grow them in large, deep containers or specially designed potato bags with great success.

By following this guide and paying attention to your local conditions, you’ll be on track for a succesful potato harvest. The simple act of digging up your own homegrown potatoes is a true garden joy.