Idaho’s high elevation and cool nights demand a later planting schedule than most potato-growing regions. Finding the best time to plant potatoes in Idaho is crucial for a successful harvest, as the state’s unique climate can easily damage tender sprouts. You want to avoid both late frosts and summer heat, so timing is everything.
Potatoes are a cool-season crop, but they can’t handle freezing temperatures. In Idaho, the growing season is short in many areas, especially in the higher valleys. The key is to plant after the soil has warmed up enough and the danger of a hard frost has passed.
This guide will walk you through the exact timing for different parts of Idaho. We’ll cover soil temperature, frost dates, and variety selection. You’ll know exactly when to put those seed potatoes in the ground.
Best Time To Plant Potatoes In Idaho
The best time to plant potatoes in Idaho is generally from mid-April to late May. This window shifts depending on your specific location within the state. Southern Idaho, with its milder climate, can plant earlier than northern regions.
For most of the state, aim for soil temperatures around 45-50°F (7-10°C) at a depth of 4 inches. If the soil is too cold and wet, the seed pieces can rot before they sprout. If you plant too late, the potatoes will struggle to mature before the first fall frost.
Here is a simple breakdown by region:
- Southern Idaho (Boise, Twin Falls): Plant from mid-April to early May.
- Central Idaho (Sun Valley, McCall): Plant from early May to late May.
- Northern Idaho (Coeur d’Alene, Moscow): Plant from late May to early June.
- Eastern Idaho (Idaho Falls, Rexburg): Plant from early May to mid-May.
Understanding Your Local Frost Dates
Your last spring frost date is your starting point. Potatoes can handle a light frost once they are established, but young shoots are very vulnerable. Wait until at least two weeks after your average last frost date to plant.
You can find your local frost dates from the Idaho State University Extension office or online gardening tools. For example, Boise’s last frost is usually around April 20, while Driggs might be as late as June 10. Adjust your planting schedule accordingly.
A good rule is to plant when the soil is workable and not muddy. If you dig a hole and water pools in it, it’s too wet. Wait a few days for the soil to dry out.
Soil Temperature: The Real Key
Soil temperature is more reliable than the calendar. A soil thermometer is a cheap tool that pays for itself. Insert it 4 inches deep in your garden bed in the morning.
Potato seed pieces need soil above 45°F to start growing. If the soil is below 40°F, the seed can rot. If it’s above 80°F, the tubers may stop forming. The sweet spot is 50-65°F for planting.
In Idaho, the soil warms up slowly in spring. You can speed things up by covering your planting area with black plastic a few weeks before planting. This traps heat and dries out the soil.
Factors That Affect Planting Time In Idaho
Several factors can shift your planting window. You need to consider your elevation, microclimate, and the specific potato variety you are growing. Idaho is not a one-size-fits-all state for gardening.
Elevation And Microclimates
Higher elevations mean cooler temperatures and later planting. A garden at 5,000 feet in Stanley will be much colder than one at 2,500 feet in Lewiston. You might need to plant 3-4 weeks later at high elevations.
Microclimates also matter. A south-facing slope warms up faster than a north-facing one. A garden near a large body of water, like Lake Coeur d’Alene, will have a slightly longer frost-free season. Observe your own yard’s conditions.
Potato Variety Selection
Different potato varieties have different maturity times. Early-season varieties like ‘Yukon Gold’ or ‘Red Norland’ mature in 70-80 days. They are great for short growing seasons. You can plant them a bit later and still get a harvest.
Main-season varieties like ‘Russet Burbank’ take 90-110 days. These need a longer, warmer season. They are common in commercial Idaho potato fields but may struggle in high-elevation home gardens. Late-season varieties like ‘Kennebec’ take even longer.
For Idaho home gardens, stick with early to mid-season varieties. This gives you a buffer against early fall frosts. You can also plant a mix to extend your harvest window.
Preparing Seed Potatoes
Before planting, you need to prepare your seed potatoes. Buy certified disease-free seed potatoes from a garden center. Do not use grocery store potatoes, as they may carry diseases.
Cut larger seed potatoes into pieces, each with at least 2-3 eyes (sprouts). Let the cut pieces sit at room temperature for 1-2 days. This allows the cut surfaces to callus over, which prevents rotting in cold soil.
Small seed potatoes can be planted whole. Plant the pieces 2-4 inches deep, with the eyes facing up. Space them 12-15 inches apart in rows that are 2-3 feet apart.
Step-By-Step Planting Guide For Idaho
Here is a step-by-step process to follow for planting potatoes in Idaho. Follow these steps, and you will have a strong start to your potato crop.
- Choose a sunny spot: Potatoes need at least 6-8 hours of direct sunlight per day. Avoid shady areas near trees or buildings.
- Prepare the soil: Loosen the soil to a depth of 8-10 inches. Remove rocks and large clumps. Potatoes grow best in loose, well-drained soil.
- Add compost: Mix in 2-3 inches of well-rotted compost or aged manure. Do not use fresh manure, as it can burn the plants.
- Check soil temperature: Use a thermometer to confirm the soil is at least 45°F at 4 inches deep. If not, wait a few more days.
- Dig trenches: Dig a trench about 4 inches deep. Place the seed potato pieces in the trench, eyes up, 12 inches apart.
- Cover lightly: Cover the seed pieces with 2-3 inches of soil. Do not fill the trench completely yet. You will mound soil later.
- Water gently: Water the area lightly after planting. Keep the soil moist but not waterlogged. Overwatering can cause rot.
- Monitor for sprouts: In 2-3 weeks, you should see green sprouts emerging. Once they are 6-8 inches tall, start hilling.
Hilling Potatoes
Hilling is the process of mounding soil around the stems as they grow. This encourages more tubers to form and prevents them from turning green from sunlight exposure. It also helps control weeds.
When the plants are 6-8 inches tall, use a hoe to pull soil from the sides of the row up around the stems. Leave only the top 2-3 inches of leaves exposed. Repeat this process every 2-3 weeks until the plants flower.
You can also use straw or mulch for hilling. This keeps the soil cooler in summer and makes harvesting easier. Just pile straw around the stems as they grow.
Common Mistakes To Avoid
Many Idaho gardeners make simple mistakes that reduce their potato yield. Avoid these common pitfalls to get a better harvest.
- Planting too early: Cold, wet soil causes seed rot. Wait until the soil is warm enough.
- Planting too deep: Deep planting delays emergence. Stick to 2-4 inches deep.
- Using grocery store potatoes: These may carry diseases or be treated with sprout inhibitors. Always use certified seed potatoes.
- Overwatering: Potatoes need consistent moisture, but soggy soil leads to rot. Water deeply once a week, not daily.
- Ignoring pests: Colorado potato beetles and aphids are common in Idaho. Check your plants weekly and hand-pick beetles or use insecticidal soap.
When To Harvest Potatoes In Idaho
Knowing when to harvest is just as important as planting at the right time. Potatoes are ready when the plants start to yellow and die back. This usually happens 70-110 days after planting, depending on the variety.
For new potatoes (small, tender ones), you can harvest them 2-3 weeks after the plants flower. Gently dig around the base of the plant and take a few tubers. Leave the rest to grow larger.
For full-sized storage potatoes, wait until the foliage has completely died back. Then, let the potatoes sit in the ground for another 2 weeks. This toughens their skins for storage.
Harvest on a dry day. Use a garden fork to gently lift the plants from the side, not from the top. Avoid stabbing the tubers. Brush off excess soil, but do not wash them until you are ready to use them.
Storing Your Potato Harvest
Proper storage extends the life of your potatoes. After harvesting, cure them in a dark, cool place (50-60°F) with high humidity for 1-2 weeks. This heals any minor cuts and thickens the skin.
After curing, store potatoes in a dark, cool location around 40-45°F. A root cellar, basement, or garage works well. Do not store them in the refrigerator, as cold temperatures turn starches into sugar.
Keep potatoes away from onions, as they release gases that cause spoilage. Check stored potatoes regularly and remove any that show signs of rot. Properly stored potatoes can last for several months.
Frequently Asked Questions
Here are some common questions about planting potatoes in Idaho.
Can I plant potatoes in Idaho in July?
It is not recommended. July is too late for most of Idaho. The growing season is too short, and the summer heat will stress the plants. Stick to spring planting for best results.
What is the best potato variety for Idaho home gardens?
Early varieties like ‘Yukon Gold’, ‘Red Norland’, and ‘Russian Banana’ are excellent choices. They mature quickly and handle Idaho’s variable weather well. ‘Russet Burbank’ is also good but needs a longer season.
How deep should I plant seed potatoes in Idaho?
Plant them 2-4 inches deep. In heavier clay soils, plant at 2 inches. In sandy loam soils, 4 inches is fine. The key is to not plant too deep, as it delays emergence.
Do I need to water potatoes in Idaho?
Yes, especially during dry spells. Idaho summers can be dry. Water deeply once a week, providing about 1-2 inches of water. Mulching helps retain moisture and keeps soil cool.
Can I grow potatoes in containers in Idaho?
Yes, containers work well. Use a large pot (at least 10 gallons) with drainage holes. Fill with loose potting soil and plant 2-3 seed pieces. Follow the same planting and hilling steps as in-ground gardens.
Final Tips For Idaho Potato Growers
Planting potatoes in Idaho is rewarding if you get the timing right. Remember that patience is key. Wait for the soil to warm up, and don’t rush the process.
Keep an eye on the weather forecast in spring. If a late frost is predicted, cover your young plants with row covers or old blankets. Remove the covers in the morning.
Rotate your potato planting location each year. Do not plant potatoes in the same spot more than once every 3-4 years. This prevents soil-borne diseases from building up.
With the right timing and care, you will enjoy a bountiful harvest of Idaho-grown potatoes. They taste much better than store-bought ones, and you control what goes into the soil. Happy planting!