When To Plant Potatoes In Montana

Knowing when to plant potatoes in Montana is the single most important factor for a successful harvest. Get the timing right, and you’ll be rewarded with a bounty of homegrown spuds perfect for storage. This guide will walk you through the simple steps to find your perfect planting window.

Montana’s climate varies dramatically, from the colder zones in the north and mountains to the slightly milder regions in the south. This means your planting date is a local decision. But don’t worry, we’ll make it easy to figure out.

Your main cue for planting potatoes is soil temperature, not just the last spring frost date. Potatoes are tough, but planting in cold, soggy soil can lead to rot.

Aim for a soil temperature of at least 45°F (7°C). You can check this with a simple soil thermometer. A good traditional rule is to plant 2-4 weeks before your area’s average last frost date. This allows the seed potato to establish roots before sending up shoots.

Finding Your Montana Planting Window

Use this general guide based on region, but always confirm with soil temp.

Western Montana & Mountain Valleys (Zones 4-5): Late April to late May. Cities like Missoula and Kalispell often plant in early to mid-May.
Central & Eastern Montana (Zones 4-5): Early to late May. For Billings, Bozeman, and Great Falls, mid-May is a common target.
Warmer Microclimates & Southern Areas (Zone 6): Mid-April to early May. Places like Helena can sometimes start a bit earlier.

If a late spring snow or hard freeze is forcasted after planting, you can protect emerging greens with a light covering of straw or a frost cloth.

Preparing Your Seed Potatoes

Start with certified disease-free seed potatoes from a garden center. Don’t use grocery store potatoes, as they are often treated to prevent sprouting.

Chitting (Pre-sprouting): About 2-4 weeks before planting, place your seed potatoes in a cool, bright spot indoors. This encourages short, sturdy green sprouts, giving them a head start.
Cutting: A day or two before planting, cut larger seed potatoes into pieces. Each piece should be about the size of a golf ball and have at least 1-2 strong “eyes” or sprouts. Let the cut pieces air-dry to form a protective callus over the cuts, which prevents rot.

Choosing the Right Potato Varieties for Montana

Selecting varieties suited to a shorter growing season and cooler nights will improve your harvest. Here are some excellent choices:

Early Season (65-80 days): ‘Yukon Gold’, ‘Red Norland’, ‘Irish Cobbler’. These are great for getting a harvest even if your summer is short.
Mid-Season (80-95 days): ‘Russet Burbank’, ‘Kennebec’, ‘Purple Majesty’. These are reliable workhorses for storage.
Late Season (95+ days): ‘Butte’, ‘Canela Russet’. Best for longer, warmer Montana valleys.

Step-by-Step Planting Guide

Site & Soil: Choose a sunny spot with well-drained soil. Potatoes thrive in loose, slightly acidic soil. Work in plenty of compost or well-rotted manure the fall before, if possible.
Trench Method: Dig a trench about 6-8 inches deep. Space trenches 2-3 feet apart.
Planting: Place seed potato pieces cut-side down, with eyes facing up, in the trench. Space them about 12 inches apart.
Covering: Cover the potatoes with 4 inches of soil. Do not fill the trench completely yet.
Watering: Water gently to settle the soil, but avoid making it soggy.

The Hilling Process: Key to Bigger Potatoes

Hilling is the practice of mounding soil around the growing stems. This protects developing tubers from sunlight (which turns them green and toxic) and encourages more potatoes to form along the buried stem.

When green shoots reach about 6-8 inches tall, gently mound soil from between the rows around the base of the plants, leaving just the top few inches exposed.
Repeat this process every few weeks until the plants begin to flower. By then, the hill should be about 6-12 inches high.
You can also use straw or shredded leaves for hilling, which makes harvest easier and keeps soil cooler.

Caring for Your Growing Potatoes

Watering: Provide 1-2 inches of water per week, especially during tuber formation (when plants flower). Consistent moisture prevents knobby potatoes. Reduce water as plants yellow and die back near harvest.
Weeding: Keep weeds down, especially early on. Hilling helps smother weeds.
Pests: Watch for Colorado potato beetles. Hand-pick them and their orange egg clusters off leaves. Crop rotation is your best defense against soil-borne dieseases.

Harvesting and Storing Your Bounty

Harvest time depends on what type of potato you want.

New Potatoes: For tender, thin-skinned “new” potatoes, you can gently dig around plants about 2-3 weeks after they stop flowering.
Storage Potatoes: For mature potatoes meant for winter storage, wait until the plant vines have completely yellowed and died back. This allows the skins to toughen up.

Choose a dry day to dig. Use a digging fork, starting far from the main stem to avoid spearing tubers. Let potatoes cure on the soil surface for a few hours, then brush off dirt and cure them in a dark, well-ventilated place at 45-60°F for 1-2 weeks. After curing, store in a cool, dark, humid place like a root cellar. Properly cured and stored potatoes can last for months.

Frequently Asked Questions (FAQ)

Can I plant potatoes in July in Montana?

Generally, no. Planting this late won’t give the tubers enough time to mature before the first fall frost, which can come early in Montana. For a fall harvest, you would need to plant a very early-season variety by early July at the absolute latest, and even that is risky.

What happens if I plant potatoes too early?

Planting in cold, wet soil is the main risk. The seed potato piece may rot before it sprouts, or the young plant’s growth will be stunted. It’s better to wait for the right soil conditions than to rush.

How do I protect potatoes from a late frost?

If green foliage emerges and a frost is predicted, cover the plants with straw, old blankets, or frost cloth overnight. The growing point is underground, so even if the tops get nipped, the plant will often send up new growth.

Can I grow potatoes in containers in Montana?

Absolutely! Using large pots or grow bags is a fantastic option, especially if you have limited space or poor soil. It also makes harvesting simple—just tip the container over. Ensure they have excellent drainage and consistent water, as containers dry out faster.

By following these guidelines and paying attention to your local conditions, you’ll master the art of timing your potato planting. The reward of digging up your own homegrown potatoes is well worth the wait. Remember, gardening is always a learning experience, so take notes on what works best in your specific Montana garden.