Wyoming’s short growing season means tomatoes should be started indoors six to eight weeks before the last frost date. Knowing the best time to plant tomatoes in wyoming is the single most important step for a successful harvest. Get this wrong, and your plants might not have enough time to produce ripe fruit before the first fall frost arrives.
Tomatoes love warmth. They need soil temperatures above 60°F and nighttime air temperatures consistently above 50°F. In Wyoming, that warm window is narrow. The key is to plan backward from your area’s average last spring frost date.
Understanding Wyoming’s Climate Zones
Wyoming is not a one-size-fits-all state for gardening. Elevation and latitude create big differences in frost dates. The eastern plains, the western basins, and the mountain valleys all have unique growing windows.
Average Last Frost Dates By Region
- Eastern Wyoming (Cheyenne, Torrington, Wheatland): May 10 to May 20
- Central Wyoming (Casper, Riverton, Lander): May 15 to May 25
- Western Wyoming (Evanston, Rock Springs, Pinedale): May 25 to June 5
- Mountain Valleys (Jackson, Cody, Laramie): June 1 to June 10
These dates are averages. A late frost can happen after these dates. A warm spring might let you plant a bit earlier. Always watch the 10-day forecast before moving plants outside.
Best Time To Plant Tomatoes In Wyoming
The absolute best time to plant tomatoes outdoors in Wyoming is after the danger of frost has passed and the soil has warmed up. For most of the state, this means transplanting hardened-off seedlings into the garden between May 20 and June 10. In colder mountain areas, wait until mid-June.
But the real secret is starting seeds indoors at the right time. If you start too early, your seedlings become leggy and root-bound. If you start too late, they won’t be big enough to handle the short season.
When To Start Tomato Seeds Indoors
- Find your area’s average last frost date (see the list above).
- Count backward 6 to 8 weeks from that date.
- For eastern Wyoming, start seeds around March 20 to April 5.
- For central Wyoming, start seeds around March 25 to April 10.
- For western and mountain areas, start seeds around April 1 to April 15.
Mark your calendar. Write it down. This is the single most important date for your tomato season.
Hardening Off Your Seedlings
You cannot just take indoor seedlings and plop them in the ground. They need to adjust to wind, sun, and cooler temps. This process takes about 7 to 10 days.
- Start about two weeks before your planned outdoor planting date.
- Place seedlings outside in a shaded, sheltered spot for 1 hour on day one.
- Add 1 hour of outdoor time each day.
- Gradually move them into more direct sunlight over the week.
- Bring them indoors if a frost is forecasted.
Hardening off reduces transplant shock. It gives your plants a much better start.
Choosing The Right Tomato Varieties For Wyoming
Not all tomatoes are equal in a short season. You need varieties that mature quickly. Look for “days to maturity” on the seed packet or plant tag. This number tells you how many days from transplanting to first ripe fruit.
Early-Maturing Varieties (50-65 Days)
- Sub-Arctic Plenty: 45 days. Very reliable in cool summers.
- Stupice: 55 days. Great flavor for an early tomato.
- Oregon Spring: 58 days. Sets fruit in cool weather.
- Glacier: 56 days. Bred for short seasons.
- Early Girl: 59 days. A classic early slicer.
Mid-Season Varieties (65-75 Days)
- Celebrity: 70 days. Disease resistant and productive.
- Better Boy: 72 days. Large fruit, good flavor.
- Roma: 75 days. Perfect for sauces and canning.
Cherry And Small-Fruited Tomatoes
Cherry tomatoes often ripen faster than large beefsteaks. They are a smart choice for Wyoming.
- Sweet 100: 65 days. Produces clusters of sweet fruit.
- Sun Gold: 57 days. Super sweet and early.
- Yellow Pear: 70 days. Fun shape and good producer.
Stick with determinate or semi-determinate varieties if you want a concentrated harvest. Indeterminate types keep growing and producing until frost, but they need a long season to reach full potential.
Preparing Your Garden Soil
Tomatoes need rich, well-drained soil. Wyoming soil is often heavy clay or sandy. Both need ammendment.
Soil Testing
Get a simple soil test from your local extension office. It will tell you pH and nutrient levels. Tomatoes prefer a pH between 6.0 and 6.8. If your soil is too acidic or alkaline, you can adjust it.
Improving Your Soil
- Add 2 to 3 inches of compost or well-rotted manure.
- Work it into the top 8 to 10 inches of soil.
- If your soil is heavy clay, add coarse sand or perlite for drainage.
- If your soil is sandy, add more organic matter to hold moisture.
Do this a week or two before you plan to transplant. Give the soil time to settle.
Planting Your Tomatoes Outdoors
When the soil is warm and the nights are above 50°F, it is time to plant.
Step-By-Step Transplanting
- Choose a sunny spot. Tomatoes need at least 8 hours of direct sun daily.
- Dig a hole deep enough to bury two-thirds of the stem. Tomatoes can grow roots along the stem.
- Remove the lower leaves from the seedling.
- Place the plant in the hole, stem buried deep.
- Fill the hole with soil and press gently.
- Water thoroughly right after planting.
Planting deep helps the plant develop a strong root system. This is important for drought tolerance and nutrient uptake.
Spacing
- Determinate tomatoes: 18 to 24 inches apart.
- Indeterminate tomatoes: 24 to 36 inches apart.
- Rows: 3 to 4 feet apart.
Good air circulation prevents disease. Don’t crowd your plants.
Protecting Tomatoes From Wyoming Weather
Wyoming weather is unpredictable. You can get a frost in June or a hailstorm in July. Be prepared.
Frost Protection
Keep row covers, old sheets, or frost blankets handy. If a late frost is forecasted, cover your plants in the evening. Remove the covers in the morning when temps rise above 40°F.
Wind Protection
Wyoming wind can shred tomato leaves and break stems. Use stakes, cages, or a trellis system. A windbreak made of burlap or a fence can help.
Heat And Hail
Summer temperatures can spike. Mulch around your plants with straw or grass clippings to keep soil cool and moist. For hail, you can use floating row covers or even old buckets placed over plants temporarily.
Watering And Fertilizing
Tomatoes need consistent moisture. Inconsistent watering causes blossom end rot and cracked fruit.
Watering Schedule
- Water deeply once or twice a week, depending on rainfall.
- Give about 1 to 2 inches of water per week.
- Water at the base of the plant, not on the leaves. Wet leaves invite disease.
- Use a soaker hose or drip irrigation for best results.
Fertilizing
Tomatoes are heavy feeders. But too much nitrogen early on gives you lots of leaves and few fruit.
- At planting: Mix a balanced fertilizer (10-10-10) into the soil.
- After first fruit sets: Switch to a fertilizer lower in nitrogen and higher in phosphorus and potassium (like 5-10-10).
- Feed every 2 to 3 weeks during the growing season.
Stop fertilizing about 2 weeks before the first expected frost. This helps the plant focus on ripening existing fruit.
Common Problems In Wyoming Tomato Gardens
Even with perfect timing, problems can arise. Here are the most common issues and how to handle them.
Blossom End Rot
A dark, leathery spot on the bottom of the fruit. It is caused by calcium deficiency and inconsistent watering. Keep soil evenly moist. Add calcium to the soil if needed.
Early Blight
Brown spots on lower leaves with concentric rings. Remove affected leaves. Improve air circulation. Mulch to prevent soil splash.
Tomato Hornworms
Large green caterpillars that eat leaves and fruit. Handpick them off. Use Bt (Bacillus thuringiensis) if the infestation is bad.
Slow Ripening
If fruit is not turning red by late summer, you can speed things up. Remove some leaves to let more sun reach the fruit. Prune off new flowers and small fruit that won’t ripen before frost.
Extending The Season
Wyoming gardeners can use tricks to get more ripe tomatoes.
Use Season Extenders
- Wall O’ Water: A plastic teepee filled with water that warms the soil and protects from frost.
- Cold frames: A simple box with a glass or plastic top.
- Low tunnels: Hoops covered with row cover or plastic.
These can add 2 to 4 weeks to your growing season at both ends.
Plant In Containers
Containers warm up faster than ground soil. You can move them to a sheltered spot if frost threatens. Use large pots (at least 5 gallons) with drainage holes.
Choose Determinate Varieties
Determinate tomatoes set all their fruit at once and ripen over a few weeks. This is perfect for a short season. You get a big harvest before frost.
Harvesting And Ripening
Harvest tomatoes when they are fully colored and slightly soft to the touch. If frost is coming, pick all fruit, even green ones.
How To Ripen Green Tomatoes
- Place them in a single layer in a cardboard box.
- Add a ripe banana or apple. The ethylene gas helps ripening.
- Store in a cool, dark place (55-70°F).
- Check every few days and remove ripe ones.
Green tomatoes can also be fried, pickled, or used in relishes. Don’t let them go to waste.
Frequently Asked Questions
Can I plant tomatoes in Wyoming in July?
It is possible but risky. You need a very early-maturing variety (under 60 days) and a warm fall. Most gardeners find June planting gives better results.
What is the best tomato variety for high altitude in Wyoming?
Sub-Arctic Plenty, Glacier, and Stupice are proven winners at high elevations. They set fruit in cool temperatures and ripen quickly.
Should I use black plastic mulch for tomatoes in Wyoming?
Yes. Black plastic warms the soil faster, suppresses weeds, and conserves moisture. It is a great tool for short-season gardens.
How do I know when soil is warm enough for tomatoes?
Use a soil thermometer. Insert it 4 inches deep. If the reading is consistently above 60°F for several days, it is safe to plant.
Can I grow tomatoes from seed directly in the ground in Wyoming?
It is not recommended. The growing season is too short. Start seeds indoors or buy transplants from a local nursery.
Final Tips For Success
Timing is everything. Mark your calendar for seed starting and transplanting. Watch the weather closely in spring and fall. Choose varieties bred for short seasons. Prepare your soil well. Protect your plants from wind and frost.
With the right plan, you can enjoy homegrown tomatoes even in Wyoming’s challenging climate. The taste of a sun-warmed tomato from your own garden is worth the effort.
Start your seeds on time. Harden them off carefully. Plant them deep after the last frost. Water consistently. Feed them right. And harvest before the first frost hits. That is the proven path to tomato success in the Cowboy State.