Wyoming’s short, cool growing season demands careful timing for sweet potato planting. Knowing the best time to plant sweet potato in wyoming is the difference between a harvest of tender tubers and a pile of frost-killed vines. Sweet potatoes need warmth and a long frost-free window, which Wyoming’s high altitude and unpredictable weather don’t naturally provide. But with the right schedule, you can still grow them successfully.
This guide walks you through exactly when to plant, how to prepare, and what to do if your season runs short. You’ll get practical, step-by-step advice that works for Wyoming’s unique climate.
Understanding Wyoming’s Growing Season For Sweet Potatoes
Wyoming’s climate is tough on warm-season crops. Sweet potatoes are tropical plants that need soil temperatures above 60°F and air temperatures consistently above 50°F. Most of Wyoming falls in USDA hardiness zones 3 to 5, with last frost dates ranging from mid-May to early June and first frost dates arriving as early as mid-September.
That gives you roughly 90 to 110 frost-free days. Sweet potatoes typically need 100 to 140 days to mature. So you’re working with a tight window. The key is to start indoors and use season-extending techniques.
Key Climate Factors
- Last spring frost: May 15 to June 10, depending on your elevation
- First fall frost: September 10 to September 30
- Average growing season: 90 to 110 days
- Soil warming: Soil in Wyoming can stay cold well into June
Best Time To Plant Sweet Potato In Wyoming
The best time to plant sweet potato in wyoming is late May to early June, after the soil has warmed to at least 60°F and all danger of frost has passed. But you can’t just drop slips into cold ground. You need to start slips indoors 6 to 8 weeks before your planned outdoor planting date.
For most of Wyoming, that means starting slips in early to mid-April. If you’re in a warmer microclimate like the lower elevations near the North Platte River, you might push planting to late May. Higher elevations in the Rockies may need to wait until mid-June.
Step-By-Step Planting Timeline
- Order sweet potato slips from a reputable supplier 8 weeks before your last frost date.
- Start slips indoors 6 to 8 weeks before outdoor planting. Use a warm, sunny spot or grow lights.
- Harden off slips for 7 to 10 days before transplanting. Gradually expose them to outdoor conditions.
- Plant outdoors when soil temperature reaches 60°F and night temperatures stay above 50°F.
- Use black plastic mulch to warm the soil and retain heat.
- Cover plants with row covers or cloches if a late frost threatens.
Soil Preparation Tips
Sweet potatoes need loose, well-drained soil. Wyoming’s heavy clay or sandy soils need amending. Mix in 2 to 3 inches of compost or aged manure before planting. Avoid high-nitrogen fertilizers, which cause lush vines but small tubers.
Raised beds work well in Wyoming because they warm up faster in spring. Build beds 8 to 12 inches high and 3 to 4 feet wide. This improves drainage and soil temperature.
Choosing The Right Sweet Potato Varieties For Wyoming
Not all sweet potatoes mature fast enough for Wyoming. Stick with short-season varieties that mature in 90 to 110 days. Here are top picks:
- Beauregard: Matures in 90 to 100 days. Reliable and productive.
- Georgia Jet: Matures in 90 days. Tolerates cooler soil.
- Centennial: Matures in 100 to 110 days. Good for northern climates.
- Vardaman: Matures in 100 days. Compact bush habit.
- Porto Rico: Matures in 100 to 110 days. Good flavor.
Avoid long-season varieties like Jewel or Covington unless you have a greenhouse or high tunnel.
Where To Buy Slips
Buy slips from a local nursery or online supplier that ships to your area. Avoid grocery store sweet potatoes, which may carry diseases or be treated with sprout inhibitors. Look for certified disease-free slips.
Starting Sweet Potato Slips Indoors
Starting slips indoors is the most important step for Wyoming gardeners. Without it, your season is too short. Here’s how:
- About 8 weeks before your last frost date, place sweet potato roots in a jar of water, half submerged. Use toothpicks to hold them in place.
- Set the jar in a warm spot (75°F to 80°F) with bright indirect light.
- Change water every few days to prevent rot.
- After 2 to 3 weeks, slips (sprouts) will appear. When they reach 6 to 8 inches long, gently twist them off the root.
- Place slips in a glass of water to grow roots. Change water every 2 days.
- Once roots are 1 to 2 inches long, they’re ready to harden off.
Alternatively, you can buy pre-started slips from a garden center. Just make sure they arrive at the right time for your planting window.
Hardening Off Slips
Hardening off is critical. Wyoming’s sun and wind can shock tender slips. Start by placing them outdoors in a sheltered spot for 1 hour on the first day. Increase exposure by 1 hour each day over 7 to 10 days. Bring them indoors at night if temperatures drop below 50°F.
Planting Sweet Potatoes Outdoors
When soil temperature reaches 60°F, it’s time to plant. Use a soil thermometer to check at 4 inches deep. Wyoming soils warm slowly, so use black plastic mulch to speed things up. Lay the mulch 2 weeks before planting.
Plant slips 12 to 18 inches apart in rows 3 to 4 feet apart. Bury the stem up to the first set of leaves. Water thoroughly after planting. Keep soil consistently moist but not waterlogged for the first 2 weeks.
Using Season Extenders
In Wyoming, season extenders are almost mandatory. Here are effective options:
- Black plastic mulch: Warms soil by 5°F to 10°F and suppresses weeds.
- Row covers: Floating fabric that traps heat and protects from wind and light frost.
- Cold frames: Mini-greenhouses that can add 2 to 4 weeks to your season.
- High tunnels: Large unheated structures that allow earlier planting and later harvest.
Caring For Sweet Potatoes During The Growing Season
Sweet potatoes need consistent care through Wyoming’s short summer. Here’s what to focus on:
Watering
Water deeply once a week, providing 1 to 2 inches of water. Drip irrigation is best because it keeps foliage dry and reduces disease. Reduce watering 2 to 3 weeks before harvest to prevent cracking.
Fertilizing
Sweet potatoes are light feeders. Apply a low-nitrogen fertilizer (5-10-10) at planting time. Side-dress with the same fertilizer 4 weeks later. Avoid too much nitrogen, which promotes leaves over tubers.
Weeding
Weeds compete for nutrients and water. Hand-weed carefully around the shallow roots. Mulch with straw or grass clippings to suppress weeds and retain moisture.
Pest And Disease Management
Common issues in Wyoming include:
- Wireworms: Soil-dwelling larvae that tunnel into tubers. Rotate crops and use beneficial nematodes.
- Flea beetles: Small holes in leaves. Use row covers or insecticidal soap.
- Root rot: Caused by overwatering or poor drainage. Plant in raised beds and avoid wet soil.
Harvesting Sweet Potatoes In Wyoming
Harvest before the first fall frost. In most of Wyoming, that’s mid-September to early October. Leaves will start to yellow, but don’t wait until they die back completely. Frost can damage tubers even if the vines look fine.
Use a garden fork to gently lift the tubers. Be careful not to bruise them. Cure the harvested sweet potatoes in a warm, humid place (80°F to 85°F, 85% humidity) for 10 to 14 days. This converts starches to sugars and heals minor wounds.
After curing, store them in a cool, dark place at 55°F to 60°F. They’ll keep for several months.
Signs It’s Time To Harvest
- Leaves begin to yellow or wilt
- Vines start to die back
- First frost is forecast within 10 days
- Tubers are at least 2 inches in diameter
Troubleshooting Common Problems
Even with perfect timing, things can go wrong. Here are fixes for common issues:
Small Tubers
If your sweet potatoes are tiny, the season was too short or soil was too cold. Next year, start slips earlier, use black plastic mulch, and choose an even faster-maturing variety like Georgia Jet.
Split Or Misshapen Tubers
Irregular watering causes cracking. Keep soil evenly moist, especially during tuber formation. Avoid heavy watering after a dry spell.
No Tubers At All
This usually means too much nitrogen or not enough sun. Sweet potatoes need full sun (8+ hours daily). Cut back on nitrogen fertilizer and ensure your site gets maximum light.
Frost Damage
If an early frost catches you, cover plants with row covers or blankets overnight. Harvest immediately after a frost, even if tubers are small. Damaged vines won’t recover.
Frequently Asked Questions
Can I plant sweet potatoes directly in the ground in Wyoming?
Yes, but only after soil warms to 60°F. Starting slips indoors is strongly recommended to extend the season.
What is the latest I can plant sweet potatoes in Wyoming?
Plant no later than June 15 to ensure enough time for tubers to mature before the first frost. In higher elevations, aim for June 1.
Do sweet potatoes need full sun in Wyoming?
Yes, they need at least 8 hours of direct sunlight daily. Less sun reduces yield and delays maturity.
Can I grow sweet potatoes in containers in Wyoming?
Yes, use a 10-gallon container with drainage holes. Fill with loose, sandy loam. Containers warm up faster than ground soil, which helps in cool climates.
How do I protect sweet potatoes from Wyoming’s wind?
Use windbreaks like fences or row covers. Wind dries out soil and damages leaves. Plant in a sheltered spot if possible.
Final Tips For Wyoming Sweet Potato Success
Growing sweet potatoes in Wyoming takes planning, but it’s doable. Start slips indoors, use black plastic mulch, and pick short-season varieties. Monitor soil temperature closely and be ready to cover plants if frost threatens.
Remember that microclimates matter. South-facing slopes, areas near buildings, or spots with reflected heat from rocks can give you an extra week or two. Experiment and keep notes on what works in your specific location.
With the right timing and a few season-extending tricks, you’ll enjoy homegrown sweet potatoes even in Wyoming’s short growing season. The effort is worth it for that first taste of a freshly dug, sweet tuber from your own garden.