Minnesota’s cold winters require waiting until late May or early June for nasturtium, when the soil has finally warmed and frost is no longer a threat. The best time to plant nasturtium in minnesota is a common question for gardeners here, and the answer hinges on our unpredictable spring weather. You want to get these colorful flowers into the ground, but rushing can kill them overnight.
Nasturtiums are tender annuals that simply cannot handle frost. Unlike some hardy vegetables, a single cold snap will turn your healthy seedlings into mushy stems. This guide will walk you through exactly when and how to plant them for success in the Land of 10,000 Lakes.
Best Time To Plant Nasturtium In Minnesota
The absolute safest window is from May 25th to June 5th for most of the state. This timing works for the Twin Cities, Rochester, and St. Cloud areas. If you live in northern Minnesota near Duluth or Bemidji, push that back by one to two weeks.
Here is the simple rule: wait until the soil temperature is consistently above 60°F (15°C). You can check this with a simple soil thermometer. Also, watch the 10-day forecast for any overnight lows below 40°F.
Why Timing Matters So Much
Nasturtiums are not just pretty faces. They are edible flowers with a peppery taste. But they are also very sensitive to cold soil. If you plant them when the ground is still chilly, the seeds will rot before they even sprout.
Planting too early leads to:
- Seed rot and no germination
- Stunted growth that never recovers
- Increased risk of pest problems like aphids
Understanding Your Minnesota Zone
Minnesota spans USDA hardiness zones 3a to 5a. The further north you go, the shorter your growing season. Your last frost date is the key number to know.
- Southern MN (Zone 5a): Last frost around May 10-15. Plant nasturtiums around May 20-25.
- Central MN (Zone 4b): Last frost around May 15-25. Plant around May 25-June 1.
- Northern MN (Zone 3b-4a): Last frost around May 25-June 5. Plant around June 1-10.
Always check your local extension office for the most accurate frost dates. They have data specific to your county.
Starting Seeds Indoors Vs Direct Sowing
You have two main options for planting nasturtiums in Minnesota. Each has its own benefits and drawbacks. Let’s look at both so you can choose what works for your situation.
Starting Nasturtium Seeds Indoors
This gives you a head start of about 4-6 weeks. It is great for impatient gardeners or those with very short summers. However, nasturtiums do not like root disturbance.
Follow these steps for indoor success:
- Use biodegradable pots like peat pots or newspaper pots.
- Plant seeds 1 inch deep, two seeds per pot.
- Keep soil moist but not soggy.
- Provide bright light immediately after sprouting.
- Harden off seedlings for 7-10 days before moving outside.
The best time to start indoors is mid-April for most of Minnesota. This gives you plants ready for late May transplanting. Remember to pinch off the first few flowers to encourage bushier growth.
Direct Sowing Nasturtium Seeds
This is the easier method and often produces stronger plants. Nasturtiums actually prefer to be left alone once planted. Direct sowing avoids transplant shock completely.
For direct sowing:
- Wait until soil temperature reaches 60°F.
- Soak seeds in water overnight to speed germination.
- Plant seeds 1 inch deep and 10-12 inches apart.
- Water gently after planting.
- Expect sprouts in 10-14 days.
Direct sowing is the most reliable method for Minnesota gardeners. The seeds are large and easy to handle. Just be patient and wait for the right conditions.
Preparing Your Minnesota Garden Soil
Nasturtiums actually prefer poor soil. Too much nitrogen makes them grow lots of leaves but very few flowers. This is a common mistake for new gardeners.
Here is what your soil needs:
- Well-draining soil that does not hold water
- Moderate fertility, not rich compost
- Neutral to slightly acidic pH (6.0-7.0)
- Full sun to partial shade
If your soil is heavy clay, mix in some sand or perlite. Nasturtiums hate wet feet. Raised beds or containers work wonderfully for them in Minnesota.
Choosing The Right Location
Nasturtiums need at least 4-6 hours of direct sunlight daily. In southern Minnesota, afternoon shade can help them survive hot July days. In northern areas, full sun is best.
Good locations include:
- Along garden borders
- In hanging baskets
- Around vegetable gardens as companion plants
- In window boxes
These plants also make excellent ground covers. They spread quickly and suppress weeds naturally.
Planting Nasturtium Step By Step
Now that you know the best time to plant nasturtium in minnesota, let’s walk through the actual planting process. Follow these steps for the best results.
Step 1: Check The Weather
Look at the 10-day forecast before planting. Avoid planting if rain is expected for several days. Wet soil plus cold nights is a recipe for disaster.
Ideal conditions are:
- Daytime temperatures above 65°F
- Nighttime temperatures above 50°F
- No frost in the forecast
- Soil that is dry enough to crumble
Step 2: Prepare The Seeds
Nasturtium seeds have a hard outer shell. Soaking them helps speed up germination. Place seeds in a bowl of warm water for 12-24 hours before planting.
You will see them swell slightly. This is normal and good. Plant them immediately after soaking. Do not let them dry out again.
Step 3: Plant At The Right Depth
Plant seeds 1 inch deep in the soil. Cover them lightly and pat down gently. Do not pack the soil too tightly. Seeds need air to germinate.
Space seeds 10-12 inches apart for bush varieties. Trailing varieties can be spaced 18-24 inches apart. They will fill in quickly.
Step 4: Water Carefully
Water the planting area gently after sowing. Use a watering can with a rose attachment to avoid washing seeds away. Keep the soil consistently moist until sprouts appear.
Once plants are established, water only when the top inch of soil feels dry. Overwatering leads to root rot and fewer flowers.
Caring For Nasturtiums After Planting
Nasturtiums are low-maintenance plants. Once they are growing, they mostly take care of themselves. However, a little care goes a long way in Minnesota.
Watering Needs
These plants are drought-tolerant once established. In Minnesota’s summer heat, water deeply once a week. More frequent watering may be needed in containers.
Signs of underwatering:
- Wilting leaves during the day
- Yellowing lower leaves
- Fewer flowers
Signs of overwatering:
- Yellow leaves that feel mushy
- Mold on soil surface
- Stunted growth
Fertilizing
Do not fertilize nasturtiums. They bloom best in poor soil. If you must feed them, use a phosphorus-rich fertilizer (the middle number) and avoid nitrogen-heavy formulas.
Too much fertilizer causes:
- Lots of leaves, few flowers
- Leggy, weak stems
- Increased aphid problems
Deadheading And Pruning
Remove spent flowers to encourage more blooms. This is called deadheading. It is simple and takes only a few minutes each week.
If plants get too leggy, trim them back by one-third. This promotes bushier growth and more flowers. Use clean scissors or pruning shears.
Common Problems With Nasturtiums In Minnesota
Even with perfect timing, problems can arise. Here are the most common issues and how to handle them.
Aphids
Nasturtiums are aphid magnets. This is actually a good thing if you use them as trap plants for your vegetables. But heavy infestations can weaken the plants.
Solutions:
- Spray with a strong stream of water
- Use insecticidal soap
- Introduce ladybugs
- Remove heavily infested leaves
Powdery Mildew
This fungal disease appears as white powder on leaves. It happens in humid conditions with poor air circulation. Minnesota summers can be humid enough to cause this.
Prevention:
- Space plants properly for air flow
- Water at soil level, not on leaves
- Plant in full sun
Slugs And Snails
These pests love tender nasturtium leaves. They are most active at night and after rain. Minnesota’s wet springs can bring them out in force.
Control methods:
- Hand pick at night
- Use beer traps
- Apply diatomaceous earth around plants
- Encourage birds and frogs in your garden
Harvesting And Using Nasturtiums
One of the best parts of growing nasturtiums is eating them. Both flowers and leaves are edible. They have a peppery, radish-like flavor.
When To Harvest
Pick flowers when they are fully open. Harvest leaves when they are young and tender. Older leaves can be tough and too spicy.
Best time to harvest:
- Early morning after dew dries
- Before the heat of the day
- When flowers are fresh and bright
How To Use Them
Nasturtiums are versatile in the kitchen. Add them to salads for color and spice. Use them as garnishes on plates. Stuff the flowers with soft cheese for appetizers.
The seeds can also be pickled and used as a caper substitute. This is a fun project for late summer when seed pods form.
Extending The Blooming Season
Minnesota’s growing season is short. You want to enjoy your nasturtiums as long as possible. Here are tips to extend their bloom time.
Plant In Succession
Plant a second batch of seeds 2-3 weeks after the first. This ensures continuous blooms from July through September. The second planting will flower later into fall.
This works well because nasturtiums grow quickly from seed. You will have fresh plants coming into bloom as the first ones start to fade.
Protect From Early Frost
Cover plants with row covers or old sheets if frost is predicted. This can extend your season by several weeks. Remove covers during the day.
Container plants can be moved indoors or to a sheltered location. This is a great option for gardeners with limited space.
Companion Planting With Nasturtiums
Nasturtiums are excellent companion plants. They repel certain pests and attract beneficial insects. Use them strategically in your vegetable garden.
Good Companions
- Tomatoes – repels whiteflies and aphids
- Cucumbers – deters cucumber beetles
- Squash – protects against squash bugs
- Broccoli – confuses cabbage moths
- Beans – attracts pollinators
Bad Companions
Avoid planting nasturtiums near:
- Potatoes – may compete for nutrients
- Fennel – inhibits growth of nearby plants
Most vegetables benefit from having nasturtiums nearby. They are like bodyguards for your garden.
Frequently Asked Questions
Can I plant nasturtium seeds in July in Minnesota?
Yes, but they may not bloom before frost. Plant by mid-July for best results. Choose fast-growing varieties for late planting.
Do nasturtiums come back every year in Minnesota?
No, they are annuals and die with frost. However, they often self-seed if you leave some seed pods on the plant. You may get volunteers next spring.
What is the latest time to plant nasturtium in Minnesota?
Early July is the latest for reliable blooms. Later than that, you risk frost before flowers appear. Stick to early June for best results.
Should I soak nasturtium seeds before planting?
Yes, soaking for 12-24 hours speeds germination. It softens the hard seed coat. Do not soak longer than 24 hours or seeds may rot.
Can nasturtiums grow in partial shade in Minnesota?
Yes, they tolerate partial shade but bloom less. Full sun is best for maximum flowers. Afternoon shade helps in hot southern areas.
Final Tips For Minnesota Gardeners
Growing nasturtiums in Minnesota is rewarding and easy. The key is patience. Wait for warm soil and frost-free nights. Your plants will thank you with months of color.
Remember these key points:
- Plant after May 25th in most areas
- Check soil temperature before planting
- Use poor soil for more flowers
- Water deeply but infrequently
- Harvest flowers and leaves for salads
Nasturtiums are forgiving plants. Even if you plant a bit late, they grow quickly and produce beautiful blooms. They are perfect for beginner gardeners and experienced pros alike.
One last tip: save some seeds from your plants at the end of the season. They are easy to collect and store. You will have free seeds for next year’s garden. Just let the seed pods dry on the plant, then collect them before they fall.
With the right timing and care, your Minnesota garden will be filled with vibrant nasturtiums all summer long. Enjoy the process and the beautiful results. Happy planting.