Mint in Zone 3A — Mountain West

Mint is a fantastic addition to any high-altitude garden. Its refreshing flavor elevates everything from summer drinks to savory dishes, and the intense sunlight we get here in the Mountain West concentrates those oils, giving you an even more potent and delicious herb. Plus, the satisfaction of snipping fresh mint on a cool summer evening is hard to beat.

Our short growing season and occasional temperature swings can be a challenge, but mint is surprisingly resilient. By starting smart and paying attention to its needs, you can enjoy a bountiful harvest even with our 96-day season.

Starting mint from seed indoors is possible, but honestly, it can be a bit finicky. If you're set on it, aim to sow seeds from late March through mid April, about eight weeks before you plan to transplant. Use seed trays with a good seed-starting mix, and provide consistent warmth and bright light – a grow light is a great investment for our late spring starts.

Keep the soil consistently moist by bottom watering; this helps prevent damping-off. Given our late spring and the fact that you can easily get starts from other gardeners or even take divisions from established plants, you might find it easier to skip this step.

Transplant your mint outdoors from early to late June, once the risk of frost has passed. Before you plant, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to our intense UV and fluctuating temperatures.

Space your mint plants 18-24 inches apart. Keep in mind that mint spreads aggressively, so consider planting it in containers to keep it from taking over your garden. You can always sink the container in the ground to make it look more natural.

Mint thrives on consistent moisture, which can be a challenge in our dry Mountain climate. Aim to keep the soil consistently moist, but not waterlogged. During our moderate summer heat, that usually translates to about 1 inch of water per week, either from rainfall or irrigation.

Check the soil moisture by sticking your finger about 2 inches deep. If it feels dry, it's time to water. Water at the base of the plant to avoid wetting the leaves, which can encourage fungal diseases in some situations, even though our humidity is low.

Signs of underwatering include wilting and yellowing leaves. Overwatering can lead to root rot, indicated by yellowing leaves and a generally unhealthy appearance. Mulching around your mint plants with a layer of compost or wood chips will help retain moisture in our dry air and suppress weeds.

Pruning mint is essential for both maintaining its shape and encouraging new growth. Throughout the growing season, harvest entire stems regularly, cutting them back to just above a leaf node. This encourages the plant to produce more leaves and keeps it from getting leggy.

Don't be afraid to cut it back aggressively if it starts to spread too much. As the first frost approaches in early September, give your mint one final haircut, removing any remaining stems. This helps the plant conserve energy for winter.

You can expect your first harvest of mint from late July through mid September, about 60 days after transplanting. The leaves are most flavorful before the plant flowers, so pinch off any flower buds to encourage continued leaf production.

Harvest by snipping off leaves and stems as needed. For larger harvests, cut entire stems a few inches above the ground. This will encourage new growth and keep your mint plant productive throughout the season.

As the first frost approaches in early September, harvest any remaining mint leaves before they are damaged by the cold. You can dry or freeze them for use throughout the winter.

Here are some common problems you might encounter with mint in the Mountain West:

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 conditions with moisture on leaves.
• How to fix/prevent it: Remove affected leaves immediately. Avoid overhead watering. Improve air circulation by spacing plants adequately. Apply sulfur or copper fungicide if needed. Rotate crops each year.

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 often the best treatment. Increase humidity around plants. Neem oil or insecticidal soap can also be effective.

Invasive Spreading

• What it looks like: Mint popping up in unwanted areas of your garden, quickly taking over.
• What causes it: Mint spreads aggressively via underground rhizomes.
• How to fix/prevent it: Plant mint in containers to contain its spread. Sink the container in the ground for a more natural look, but make sure the rim is above soil level. Regularly monitor and remove any runners that escape the container.

Powdery Mildew

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

Mountain West Specific Challenges: Our moderate-at-altitude summer heat and low humidity can make mint susceptible to spider mites, so keep a close eye on your plants and water regularly. The intense sun also means that plants in full sun will need more consistent watering.

Mint is a great companion plant for tomatoes and peppers. Its strong scent can help deter pests like aphids and cabbage moths, which can be a real nuisance in our gardens. It also benefits cabbage and broccoli in much the same way.

Avoid planting mint near parsley or chamomile. Mint can inhibit the growth of parsley, and chamomile prefers drier conditions than mint.