Idaho’s variable weather makes late spring the ideal window for planting nasturtium seeds. Knowing the Best Time To Plant Nasturtium In Idaho can mean the difference between a vibrant garden and a disappointing patch of leaves.
Nasturtiums are one of the easiest flowers to grow. They add color to your garden and spice to your salad. But timing matters, especially in Idaho’s unpredictable climate.
This guide walks you through exactly when to plant. We cover frost dates, soil temperatures, and even some tricks for a longer bloom season.
Understanding Idaho’s Climate Zones
Idaho is not a one-size-fits-all state. The climate changes a lot from north to south. You need to know your zone first.
Northern Idaho Growing Conditions
Northern Idaho has colder winters and cooler springs. The last frost often comes in late May. Some areas even see frost in early June.
Planting too early here is risky. The soil stays cold and wet. Nasturtium seeds can rot before they sprout.
Southern Idaho Growing Conditions
Southern Idaho is drier and warmer. The last frost usually happens in mid-to-late April. But don’t trust the calendar alone.
Cold snaps can happen. A late frost in May is not uncommon. Always check the 10-day forecast before planting.
Mountain And High Elevation Areas
If you live above 5,000 feet, your growing season is short. The last frost can be as late as June 15. Your best bet is to start seeds indoors.
Even then, wait until the soil warms up. Cold mountain soil can stunt nasturtium growth.
Best Time To Plant Nasturtium In Idaho
The exact timing depends on your location. But here is the general rule: wait until after the last frost date. Then, make sure the soil is at least 55°F (13°C).
For Direct Sowing Outdoors
Direct sowing is the easiest method. Nasturtiums don’t like having their roots disturbed. So planting them straight in the ground works best.
- Northern Idaho: Aim for late May to early June
- Southern Idaho: Aim for mid-April to early May
- Mountain areas: Aim for mid-June to late June
But these are just guidelines. Watch your local weather. If a cold spell is coming, wait a few more days.
For Starting Seeds Indoors
Starting indoors gives you a head start. You can plant seeds 4 to 6 weeks before the last frost. Use peat pots to avoid root disturbance.
- Fill pots with seed-starting mix
- Plant seeds ½ inch deep
- Water lightly and cover with plastic
- Place in a warm spot (65-70°F)
- Remove plastic once seedlings appear
- Harden off plants for a week before transplanting
Transplanting nasturtiums can be tricky. They have delicate roots. Handle them gently or you might kill them.
For Fall Planting
Fall planting is possible in warmer parts of Idaho. But it’s not common. Nasturtiums are frost-tender. A hard freeze will kill them.
If you want fall blooms, plant in late summer. Aim for August. This gives them time to grow before the first frost in October.
Checking Soil Temperature
Soil temperature matters more than air temperature. Nasturtium seeds need warmth to germinate. Cold soil leads to rot and poor growth.
How To Test Soil Temperature
You can buy a soil thermometer for cheap. Stick it 2 inches into the ground. Take the reading in the morning for accuracy.
No thermometer? Use this trick. Press your hand on the soil. If it feels cold and damp, it’s too early. Wait until the soil feels warm and crumbly.
Ideal Soil Temperature Range
Nasturtiums germinate best between 55°F and 65°F. They can handle a bit cooler, but growth will be slow. Above 70°F, they germinate fast but may get leggy.
If your soil is too cold, warm it up. Cover the planting area with black plastic for a week. This traps heat and speeds up warming.
Frost Dates Across Idaho
Knowing your local frost dates is crucial. Here are average dates for major Idaho cities.
Boise And Treasure Valley
Last spring frost: April 15 to April 25. First fall frost: October 10 to October 20. This gives you a long growing season.
Plant nasturtiums in late April. You can push it to early May if the weather is cool.
Idaho Falls And Eastern Idaho
Last spring frost: May 15 to May 25. First fall frost: September 15 to September 25. The season is shorter here.
Plant in late May or early June. Use fast-growing varieties for best results.
Coeur D’Alene And Northern Idaho
Last spring frost: May 20 to June 1. First fall frost: September 25 to October 5. You have a narrow window.
Plant in early June. Consider starting seeds indoors to extend the season.
Twin Falls And Magic Valley
Last spring frost: April 25 to May 5. First fall frost: October 1 to October 10. Similar to Boise but slightly cooler.
Plant in early May. Watch for late frosts in the higher elevations nearby.
Preparing Your Garden For Planting
Good preparation leads to healthy plants. Nasturtiums are not fussy, but they appreciate a little effort.
Choosing The Right Location
Nasturtiums need full sun for best blooms. They can handle partial shade, but you’ll get more leaves than flowers. Pick a spot with at least 6 hours of direct sunlight.
They also prefer poor to average soil. Rich soil makes them grow lots of leaves and few flowers. So don’t fertilize too much.
Soil Preparation Steps
Nasturtiums like well-draining soil. Heavy clay can cause root rot. If your soil is clay, mix in some sand or compost.
- Clear the area of weeds and rocks
- Loosen the soil to 6 inches deep
- Mix in a thin layer of compost (optional)
- Rake the surface smooth
- Water the area lightly before planting
Don’t add too much nitrogen. It encourages leaf growth at the expense of flowers. A balanced fertilizer is fine, but skip it if your soil is decent.
Seed Preparation Tips
Nasturtium seeds have a hard outer shell. Soaking them overnight can speed up germination. Place seeds in warm water for 12 to 24 hours.
Some gardeners nick the seed coat with a nail file. This helps water penetrate. But be careful not to damage the inner seed.
After soaking, plant immediately. Don’t let them dry out again.
Planting Nasturtiums Step By Step
Follow these steps for a successful planting. It’s simple and takes only a few minutes.
Spacing And Depth
Plant seeds ½ to 1 inch deep. Space them 10 to 12 inches apart. If you’re planting in rows, keep rows 12 inches apart.
For bush varieties, closer spacing works. For trailing types, give them more room. They can spread up to 3 feet wide.
Watering After Planting
Water the soil gently after planting. Use a spray nozzle to avoid washing seeds away. Keep the soil moist but not soggy.
Seeds usually germinate in 7 to 14 days. Keep watering if there’s no rain. Once seedlings appear, water less often.
Thinning Seedlings
If multiple seeds sprout in one spot, thin them out. Keep the strongest seedling. Cut the others at soil level with scissors.
Don’t pull them out. Pulling can disturb the roots of the remaining plant. Thinning gives each plant room to grow.
Caring For Nasturtiums After Planting
Nasturtiums are low-maintenance. But a little care goes a long way. Here’s what to do after they sprout.
Watering Schedule
Water deeply once a week. If it’s hot and dry, water twice a week. Nasturtiums prefer consistent moisture but not wet feet.
Check the soil before watering. Stick your finger 1 inch deep. If it feels dry, water. If it’s damp, wait a day.
Fertilizing Needs
Skip the fertilizer. Nasturtiums bloom best in lean soil. Too much fertilizer leads to lush leaves and few flowers.
If your soil is very poor, add a little compost at planting time. That’s usually enough for the whole season.
Deadheading For More Blooms
Remove spent flowers to encourage more blooms. Pinch them off at the stem. This tells the plant to keep producing flowers.
If you want seeds, leave some flowers to dry. The seeds are easy to collect and store for next year.
Pest And Disease Management
Aphids love nasturtiums. But that’s actually a good thing. They act as a trap crop, keeping aphids away from your vegetables.
If aphids get out of control, spray them off with water. Use insecticidal soap if needed. Nasturtiums rarely get serious diseases.
Watch for powdery mildew in humid weather. Space plants well for air circulation. Water at the base to keep leaves dry.
Common Mistakes When Planting In Idaho
Even experienced gardeners make errors. Here are the most common ones with nasturtiums in Idaho.
Planting Too Early
This is the biggest mistake. Idaho’s spring weather is fickle. A warm week in April can fool you into planting too soon.
Then a cold snap hits. Seeds rot or seedlings die. Always wait until the soil is warm and frost is past.
Overwatering
Nasturtiums don’t like soggy soil. Overwatering leads to yellow leaves and root rot. Water only when the top inch of soil is dry.
In Idaho’s clay soils, drainage is key. Amend your soil if it holds water too long.
Using Rich Soil
Rich soil sounds good, but it’s not for nasturtiums. They respond to high nitrogen by growing huge leaves. Flowers become scarce.
Plant them in average soil. If your garden is heavily amended, plant nasturtiums in a less fertile spot.
Ignoring Sun Requirements
Nasturtiums need full sun for best blooms. Shade leads to leggy growth and few flowers. If your garden is shady, choose a different flower.
In Idaho’s high altitude, the sun is intense. Some afternoon shade can help in very hot areas. But morning sun is essential.
Extending The Bloom Season
You can enjoy nasturtiums longer with a few tricks. Here’s how to stretch the season from spring to fall.
Succession Planting
Plant seeds every 2 to 3 weeks. This ensures continuous blooms. When one batch fades, another is just starting.
Start in late spring and continue until mid-summer. The last planting should be in July for fall blooms.
Using Containers
Containers warm up faster than garden soil. You can plant nasturtiums in pots earlier in the season. Move them indoors if frost threatens.
Containers also let you control soil quality. Use a well-draining potting mix. Don’t use garden soil in pots.
Providing Shade In Hot Weather
Idaho summers can be hot. Nasturtiums may stop blooming in extreme heat. Provide light afternoon shade to keep them going.
Mulch around the base to keep roots cool. Water consistently during heat waves.
Overwintering Indoors
You can bring nasturtiums indoors for winter. Take cuttings in late summer. Root them in water and plant in pots.
Keep them in a sunny window. They’ll bloom through winter if given enough light. This works best with compact varieties.
Harvesting And Using Nasturtiums
Nasturtiums are edible and beautiful. Here’s how to use them in your kitchen and garden.
Harvesting Flowers And Leaves
Pick flowers in the morning when they’re fresh. Rinse gently and use immediately. They add a peppery kick to salads.
Leaves are also edible. Use young leaves for a milder flavor. Older leaves can be tough and spicy.
Collecting Seeds For Next Year
Let some flowers go to seed. The seeds are large and easy to collect. Wait until they turn brown and fall off easily.
Dry seeds for a week on a paper towel. Store in a cool, dark place. They stay viable for 3 to 5 years.
Culinary Uses
Nasturtium flowers are great in salads, sandwiches, and soups. They taste like watercress with a hint of sweetness. Use them as a garnish or mix into butter.
Pickled nasturtium seeds are a substitute for capers. Soak fresh seeds in vinegar for a week. They make a tangy addition to dishes.
Frequently Asked Questions
Can I Plant Nasturtiums In Idaho In July?
Yes, but you’ll have a shorter bloom season. July planting works best in southern Idaho. Choose fast-growing varieties and water regularly.
Do Nasturtiums Come Back Every Year In Idaho?
No, they are annuals in Idaho. They die with the first hard frost. But they self-seed easily. You might see volunteers next spring.
What Happens If I Plant Nasturtiums Too Early In Idaho?
Seeds may rot in cold, wet soil. Seedlings can be killed by a late frost. Always wait until the soil is warm and frost is past.
Should I Soak Nasturtium Seeds Before Planting In Idaho?
Soaking helps germination, especially in cool soil. Soak seeds for 12 to 24 hours in warm water. Plant immediately after soaking.
Can Nasturtiums Grow In Idaho’s High Altitude?
Yes, but with care. Start seeds indoors and transplant after frost. Choose compact varieties. Provide some wind protection.
Final Thoughts On Planting Nasturtiums In Idaho
Timing is everything with nasturtiums in Idaho. Wait for warm soil and safe frost dates. Your patience will be rewarded with vibrant blooms.
These flowers are forgiving and fun to grow. They add color to your garden and flavor to your meals. Follow this guide and you’ll have success.
Remember to check your local frost dates. Use a soil thermometer if you’re unsure. And don’t be afraid to experiment with different varieties.
Nasturtiums are a great choice for Idaho gardeners. They thrive in our climate with minimal effort. Plant them at the right time and enjoy the show.