Mint in Zone 7B — Pacific Northwest

Mint is a fantastic addition to any Pacific Northwest garden. Its refreshing flavor elevates everything from summer cocktails to lamb dishes, and the ease of growing it makes it incredibly rewarding. Plus, the cool nights we often get in our mild summers here in the PNW actually enhance the flavor of many herbs, including mint.

While we might not get the scorching heat of other regions, we still have to be mindful of our climate. Our wet springs and relatively dry summer months mean that careful watering and monitoring are key. With our 193-day growing season, you'll have plenty of time to enjoy your mint.

Starting mint indoors is certainly an option, but honestly, it's usually not necessary here. You can easily purchase starts from a local nursery, or even better, get a division from a gardening friend—mint is more than willing to share! However, if you're determined to start from seed, aim for mid-February through early March, about 8 weeks before you plan to transplant.

Use seed trays with a good seed-starting mix, provide warmth (a heat mat helps), and ensure they get plenty of light, especially with our overcast spring days. Bottom watering is a great way to keep the soil consistently moist without overwatering. Remember, our springs can be slow to warm up, so be patient.

Transplant your mint outdoors from mid-April through mid-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 cooler temperatures and stronger sunlight.

Space your mint plants about 18-24 inches apart. Be warned: mint spreads aggressively! Consider planting it in a container to keep it from taking over your garden beds. At transplant time, keep an eye on the weather; a late cold snap can still happen, so be ready to cover your young plants if needed.

Mint loves consistent moisture, but in the Pacific Northwest, we need to be smart about watering. During our wet springs, you might not need to water much at all. Let the rain do its job! Once the dry summer months arrive, check the soil regularly.

Stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Aim for about 1 inch of water per week, either from rainfall or irrigation. Water at the base of the plant to avoid wetting the leaves, which can encourage fungal diseases in our sometimes humid, dry-summer conditions.

Overwatering can lead to root rot, while underwatering will cause the leaves to wilt and turn yellow. A layer of mulch, like shredded bark or compost, can help retain moisture and keep the soil cool during the mild heat of summer.

Pruning mint is essential, not just for harvesting, but also for controlling its rampant growth. Throughout the growing season, regularly harvest entire stems, cutting them back to just above a leaf node. This encourages bushier growth and prevents flowering, which can diminish the flavor of the leaves.

Don't be afraid to cut it back aggressively! If you notice your mint starting to spread beyond its designated area, prune back the runners. As the first frost approaches around late October, give your mint a final trim. You can either leave it to overwinter or harvest the remaining leaves for drying or freezing.

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

To harvest, simply snip off stems with scissors or garden shears. Regular harvesting encourages continued production, so don't be shy! Pinch off any flower buds as they appear to keep the plant focused on leaf production.

As the end of the season approaches and the first frost threatens in late October, harvest as much mint as you can. You can dry the leaves, freeze them, or make mint-infused vinegar or oil to enjoy throughout the winter.

Here are some common problems you might encounter with mint in the Pacific Northwest:

Rust

• What it looks like: Rusty orange, yellow, or brown pustules on the leaves and stems, mostly on the undersides. The leaves will yellow and drop prematurely.
• What causes it: Rust fungi thrive in warm, humid conditions with moisture on the leaves.
• How to fix/prevent it: Remove affected leaves. Avoid overhead watering. Improve air circulation by spacing plants properly. Apply sulfur or copper fungicide if necessary. Don't work among wet plants to avoid spreading the spores. Rotate crops to prevent buildup in the soil.

Spider Mites

• What it looks like: Fine stippling (tiny white dots) on the leaves, fine webbing on leaf undersides and between stems. Leaves turn bronze or yellow.
• What causes it: These tiny arachnids thrive in hot, dry conditions, and populations can explode if the plant becomes drought stressed.
• How to fix/prevent it: A strong spray of water (daily for a week) is often the best treatment. Increase humidity around the plant. Neem oil or insecticidal soap can also be used. You can even release predatory mites to control the population.

Invasive Spreading

• What it looks like: Mint popping up everywhere you don't want it!
• What causes it: Mint sends out underground runners that can quickly colonize a large area.
• How to fix/prevent it: The best prevention is to plant mint in a container, either above ground or buried in the garden. If it's already spreading, dig up the unwanted runners and be diligent about removing any new shoots that appear.

Powdery Mildew

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

Pacific Northwest Specific Challenges: While we avoid the extreme heat that can plague other regions, our mild summers and dry-summer rainfall can still present challenges for mint. The humidity, though lower than in other areas, can still create conditions favorable for rust and powdery mildew. Consistent monitoring and proper watering practices are key to keeping your mint healthy and productive in the PNW.

Mint is a great companion plant for tomatoes and peppers. Its strong scent can help deter pests like aphids and flea beetles. It also benefits cabbage and broccoli, as it can repel cabbage moths.

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