Mint in Zone 5A — Great Plains

Mint is a fantastic addition to any Great Plains garden. Its refreshing flavor elevates everything from summer drinks to savory dishes, plus it's incredibly satisfying to snip fresh herbs right from your yard. Imagine a cool glass of mint-infused iced tea on a hot summer evening – grown with your own mint!

We know our region throws curveballs with extreme temperature swings and variable rainfall. But with careful timing and a little planning, you can absolutely grow thriving mint within our roughly 168-day growing season.

Starting mint indoors is an option, but honestly, it's often easier to buy a start from a local nursery or get a division from a gardening friend. If you're determined to start from seed, begin in late February through mid March, about eight weeks before you plan to transplant outdoors.

Use seed trays with a good seed-starting mix. Keep them warm and provide plenty of light, either from a sunny window or grow lights. Bottom watering helps prevent damping-off – set the tray in a shallow dish of water and let the soil soak it up from the bottom. Remember that our spring weather can be unpredictable, so keep an eye on the forecast.

Transplant your mint outdoors in late April through late May, after the last expected frost. Before planting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Space plants 18-24 inches apart. Mint is notorious for spreading, so consider planting it in a container to keep it contained. Our spring can bring late frosts, so be prepared to cover your young plants if necessary.

Mint likes consistent moisture, which can be a challenge with our variable Great Plains rainfall. Aim to keep the soil consistently moist, but not soggy. During the hottest parts of summer, you'll likely need to water deeply several times a week.

Use the "finger test" to check soil moisture – stick your finger about two inches into the soil. If it feels dry, it's time to water. Generally, aim for about 1-2 inches of water per week, depending on rainfall. Water at the base of the plant to avoid wetting the leaves, which can encourage fungal diseases in our sometimes humid conditions.

Watch for signs of underwatering, like wilting leaves, or overwatering, like yellowing leaves. A layer of mulch, like straw or shredded bark, can help retain moisture in the soil and suppress weeds, especially during our hot summers.

Pruning mint is essential, mostly to keep it from taking over your garden. Throughout the growing season, regularly harvest entire stems for use. This encourages bushier growth and prevents the plant from flowering, which can diminish the flavor of the leaves.

Don't be afraid to cut it back aggressively. In the fall, as the first frost approaches around early October, you can cut the entire plant back to a few inches above the ground. It will likely return the following spring.

You can expect your first harvest of mint in late June through mid August, about 60 days after transplanting. The best time to harvest is before the plant flowers, as the leaves are most flavorful then. Look for healthy, vibrant leaves.

Simply snip off stems as needed, leaving a few inches of growth at the base of the plant. Pinch off any flower buds to encourage continued leaf production. As the first frost approaches in early October, harvest as much mint as you can and preserve it by drying or freezing.

Here are some common problems you might encounter growing mint in the Great Plains:

Rust

• What it looks like: Rusty orange, yellow, or brown pustules on leaves and stems, mostly on undersides. Leaves yellow and drop prematurely.
• What causes it: Various rust fungi that spread via wind-borne spores. Favored by warm, humid conditions with moisture on leaves.
• How to fix/prevent it: Remove affected leaves. Avoid overhead watering. Improve air circulation. Apply sulfur or copper fungicide. Don't work among wet plants. Rotate crops.

Spider Mites

• What it looks like: Fine stippling on leaves (tiny white dots). Fine webbing on leaf undersides and between stems. Leaves turn bronze or yellow.
• What causes it: Tiny arachnids that thrive in hot, dry conditions. Populations explode in drought stress.
• How to fix/prevent it: Strong water spray (daily for a week) is the best treatment. Increase humidity around plants. Neem oil or insecticidal soap. Release predatory mites (Phytoseiulus persimilis). Avoid broad-spectrum pesticides that kill predators.

Invasive Spreading

• What it looks like: Mint popping up everywhere you don't want it.
• What causes it: Underground runners that spread aggressively.
• How to fix/prevent it: Plant in containers or raised beds to contain the spread. Regularly pull up unwanted shoots.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems, and sometimes fruit. Leaves curl, yellow, and die. Reduces plant vigor.
• What causes it: Various fungi that thrive in warm days, cool nights, and moderate humidity. Dry leaf surfaces actually favor it (unlike most fungi).
• How to fix/prevent it: Improve air circulation through spacing and pruning. Remove affected leaves. Neem oil or potassium bicarbonate sprays help. Milk spray (1 part milk to 9 parts water) is surprisingly effective. Plant resistant varieties.

Great Plains Specific Challenges: Our hot summers, low-to-moderate humidity, and variable rainfall can create conditions that favor both spider mites (during dry spells) and powdery mildew (when we have periods of humidity). Be vigilant about monitoring your plants and adjust your watering and pruning practices accordingly. Wind protection is essential to keep plants healthy and prevent spreading.

Mint is a helpful companion for tomatoes and peppers, as its strong scent can deter pests like aphids and flea beetles. It also benefits cabbage and broccoli by repelling cabbage moths.

Avoid planting mint near parsley or chamomile. Mint can inhibit the growth of parsley, and chamomile prefers drier conditions than mint. Keeping these plants separated will ensure they both thrive in your Great Plains garden.