Lemon Balm in Zone 7B — Pacific Northwest

Lemon balm is a fantastic addition to any Pacific Northwest garden. Its bright, lemony flavor shines in teas, salads, and even desserts, and its calming scent is a treat when you're working in the garden on those overcast spring days. Plus, the satisfaction of snipping fresh herbs from your own backyard, especially when our mild summers mean less watering, is hard to beat.

While we might struggle with heat-loving plants, lemon balm thrives here. Our 193-day growing season gives you plenty of time to enjoy it. Just keep an eye out for the challenges it can bring. You'll be harvesting fragrant leaves well into the fall.

Starting lemon balm indoors gives you a head start, but it's not strictly necessary in our Zone 7B climate. If you want a jump on the season, aim to sow seeds indoors from late February through mid March, about six weeks before you plan to transplant. Use seed trays with a good seed-starting mix, provide gentle warmth (a heat mat is helpful), and ensure they get plenty of light, either from a sunny window or a grow light.

Bottom watering is ideal; just set the tray in a shallow dish of water and let the soil soak it up. Starting early can be tricky, though. Overcast spring days mean seedlings can get leggy without supplemental light.

Transplant your lemon balm seedlings outdoors from mid April through mid May, once the danger of hard frost has passed. Before planting, harden them off 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 to allow for their mature size. Keep an eye on the weather forecast – those late spring cold snaps can still happen, so be prepared to cover your transplants if needed.

Direct sowing lemon balm is a simple and effective method here in the Pacific Northwest. Sow seeds from mid April through early August, once the soil has warmed up a bit. Choose a spot with full sun to partial shade.

Prepare the soil by loosening it and removing any weeds. Sow seeds thinly and cover them with a light layer of soil. Keep the soil consistently moist until germination. Remember to thin seedlings to 18-24 inches apart as they grow.

Lemon balm enjoys consistent moisture, but it doesn't like to be waterlogged. Our mild summers and dry-summer humidity mean you'll likely need to water less frequently than in hotter, more humid climates. During the wet springs, you may not need to water at all.

A good rule of thumb is to check the soil moisture about two inches deep – the "finger test." If it feels dry, it's time to water. Aim for about 1 inch of water per week during the dry summer months. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot. A layer of mulch around the base of the plants helps retain moisture and suppress weeds, especially during our dry summer months.

Lemon balm benefits from regular pruning to keep it from getting leggy and to encourage fresh growth. In midsummer, cut the plant back by about half to maintain a compact shape. This also helps prevent it from flowering, which can make the leaves taste bitter.

Remove any flower stalks as soon as you see them to keep the plant focused on leaf production. At the end of the season, around the time of our first frost in late October, you can give the plant a final trim to tidy it up. Don't cut it back too severely, though, as it needs some foliage to overwinter successfully.

You can start harvesting lemon balm leaves as early as late June, about 70 days after sowing. The best flavor is usually before the plant flowers, so harvest regularly to encourage leaf production. Look for healthy, vibrant green leaves.

To harvest, simply snip off stems with scissors or garden shears, taking care not to damage the main plant. Lemon balm is best used fresh, as it loses its flavor when dried. However, if you have a bumper crop, you can freeze the leaves for later use. As our first frost approaches in late October, harvest any remaining leaves to use or preserve.

Lemon balm, while generally easy to grow, can present a few challenges in the Pacific Northwest: aggressive spreading, bolting, and powdery mildew.

Aggressive Spreading

• What it looks like: Lemon balm spreads quickly via rhizomes (underground stems), popping up in unwanted areas of your garden.
• What causes it: It's a vigorous grower and can easily overtake nearby plants if not contained.
• How to fix/prevent it: Plant it in a container or raised bed to restrict its spread. Regularly pull up any unwanted shoots.

Bolting

• What it looks like: The plant sends up a flower stalk prematurely. Leaves become bitter or tough.
• What causes it: Triggered by heat. Even our mild summers can sometimes cause bolting if the plant is stressed.
• How to fix/prevent it: Provide afternoon shade during the hottest part of the day. Keep the soil consistently moist. Remove flower stalks as soon as you see them.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves and stems.
• What causes it: Fungi that thrive in warm days, cool nights, and moderate humidity.
• How to fix/prevent it: Improve air circulation by spacing plants adequately. Remove affected leaves. Apply neem oil or potassium bicarbonate sprays.

Pacific Northwest Specific Challenges: The dry-summer humidity can actually favor powdery mildew, so ensure good air circulation. While late blight is a major concern for tomatoes and potatoes, it doesn't directly affect lemon balm, but it's a reminder that good garden hygiene is always important.

Lemon balm is a helpful companion plant for several vegetables in the Pacific Northwest. It's a good neighbor to tomatoes because it repels tomato hornworms. Squash also benefits, as lemon balm deters squash bugs and vine borers.

Broccoli and cauliflower appreciate lemon balm nearby, as it can help repel cabbage moths. Avoid planting lemon balm near rue, as they can inhibit each other's growth.