Mint in Zone 3B — Great Plains

Mint is a must-have for any Great Plains garden. Its refreshing flavor elevates everything from summer drinks to savory dishes, and the vigorous growth provides a constant supply. Plus, there's a simple satisfaction in growing something so useful in your own backyard.

Our short growing season and extreme weather can be a challenge, but starting mint indoors gives you a head start. With a little planning, you can enjoy fresh mint from mid-summer right up until the first frost. That 118-day growing season is plenty of time!

Starting mint from seed indoors in the Great Plains gives you a jump on our short season. It's especially helpful if you want a specific variety that's hard to find as starts. Otherwise, getting divisions from a gardening friend is the easier way to go.

Start your seeds indoors from mid-March through early April, about eight weeks before you plan to transplant. Use seed trays with a good seed-starting mix, and keep them warm and consistently moist. Bottom watering is a great way to avoid damping off – just set the tray in a shallow dish of water until the soil surface looks damp. Remember our springs often have temperature swings, so a heat mat can help maintain consistent warmth for germination.

Transplant your mint outdoors from mid-May through mid-June, 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 intense Plains sunshine and wind.

Space your mint plants 18-24 inches apart. Be warned: mint spreads aggressively! Consider planting it in containers to keep it from taking over your entire garden. Keep an eye on the weather forecast; even in late spring, we can get surprise hail or late frosts.

Mint loves consistent moisture, which can be a challenge in our variable Great Plains climate. While some years we get ample rain, others are dry, so monitoring soil moisture is key. Aim to keep the soil consistently moist, but not waterlogged.

During the hot summer months, you'll likely need to water your mint every few days, especially if it's in full sun. Use the "finger test" – stick your finger into the soil about two inches deep. If it feels dry, it's time to water. A good rule of thumb is to provide about 1 inch of water per week, either through rainfall or irrigation.

Water at the base of the plant to avoid wetting the leaves, especially later in the day. With our low-to-moderate humidity, overhead watering isn't as risky as in more humid climates, but it can still encourage fungal diseases. Mulching around your mint plants with straw or wood chips helps retain moisture and suppress weeds, which is especially helpful during dry spells.

If the leaves start to wilt and turn yellow, you're likely overwatering. If the leaves are dry and crispy, you're underwatering. Adjust your watering schedule accordingly.

Pruning mint is essential for controlling its spread and encouraging bushier growth. It's a vigorous plant, so don't be afraid to cut it back hard. Regular harvesting counts as pruning!

Throughout the growing season, harvest entire stems as needed, cutting them back to just above a leaf node. This encourages new growth from the nodes below. Pinch off any flower buds as they appear to keep the plant focused on producing leaves. As the first frost approaches in mid- September, give your mint a final haircut, removing any remaining stems. This encourages the plant to focus its energy on root growth for overwintering.

You can expect your first harvest of mint from mid-July through early September, about 60 days after transplanting. The leaves are most flavorful before the plant flowers. Pinching off flower buds keeps the plant producing leaves.

Harvest mint by cutting entire stems, leaving a few inches of growth at the base of the plant. This encourages new growth and keeps the plant productive. You can harvest mint continuously throughout the growing season.

As the first frost approaches in mid- September, harvest as much mint as you can and preserve it by drying, freezing, or making mint extract.

Mint is generally easy to grow, but here are some common problems you might encounter 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. Our variable weather can create these conditions.
• 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. The dry conditions we often experience in the Plains make mint susceptible.
• 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: Mint spreads aggressively via underground runners. If left unchecked, it will take over your garden.
• How to fix/prevent it: Plant mint in containers to restrict its spread. If planted in the ground, install a physical barrier around the planting area, burying it at least 12 inches deep. Regularly monitor for and remove any unwanted growth.

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). This combination of conditions can occur in our region.
• 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 mean that mint can be stressed by both drought and fungal diseases. Careful monitoring of soil moisture and good air circulation are key to keeping your mint healthy. The wind can also exacerbate drought stress, so consider providing some wind protection.

Mint is a great companion plant for many vegetables in the Great Plains garden. It repels pests like cabbage moths and aphids, which can be a problem for cabbage and broccoli. Planting mint near tomatoes and peppers can deter flea beetles and other pests. Plus, the strong scent of mint can help mask the scent of these plants, making them less attractive to pests.

Avoid planting mint near parsley and chamomile. Mint can inhibit the growth of parsley. Chamomile also prefers drier conditions than mint, so they don't make good companions.