Lemon Balm in Zone 8A — Northern California

Lemon balm is a fantastic addition to any Northern California garden. Its bright, lemony flavor is delicious in teas, salads, and even cocktails, and it's incredibly easy to grow in our Mediterranean climate. Plus, the bees absolutely love it, which is always a bonus for a healthy garden ecosystem.

We all know gardening here comes with its own set of challenges, from drought to unpredictable heat spikes. But with a little planning, and understanding our long 255-day growing season, lemon balm is a rewarding and relatively low-maintenance herb to cultivate.

Starting lemon balm indoors gives you a head start, but it's not strictly necessary in our mild climate. If you want to get a jump on the season, sow seeds indoors from mid-January through early February, about six weeks before the last expected frost. Use seed trays filled with a good seed-starting mix, and keep them in a warm spot (around 70°F) with plenty of light – a sunny windowsill or under grow lights works well.

Remember to keep the soil consistently moist, but not soggy. Bottom watering can help prevent damping off. Our early springs mean you can get transplants in the ground early, giving them plenty of time to establish before the summer heat.

Transplanting lemon balm outdoors is best done from early March through early April. Before planting, be sure to harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind, preventing transplant shock.

When planting, space your lemon balm plants 18-24 inches apart to give them room to grow. Keep an eye on the weather forecast – those early spring temperature swings can still happen, so be prepared to cover your seedlings if a late frost is predicted.

Direct sowing lemon balm is a simple and effective method in our region. Sow seeds directly into the garden from early March through late August. Choose a spot with well-drained soil and either full sun or partial shade. Prepare the soil by loosening it and removing any weeds or debris.

Keep the soil consistently moist until the seedlings emerge, which usually takes about a week or two. Thin the seedlings to 18-24 inches apart once they are a few inches tall. Direct sowing is a great option if you have limited space indoors or simply prefer a more hands-off approach.

Lemon balm appreciates consistent moisture, especially during our dry summers. While it's not as drought-tolerant as some other Mediterranean herbs, it's relatively easy to keep happy with a good watering routine. During the hotter months, you'll likely need to water deeply a couple of times a week.

The "finger test" is a reliable way to check if your lemon balm needs water. Stick your finger about two inches into the soil – if it feels dry, it's time to water. Aim for about an inch of water per week, adjusting based on rainfall and temperature. Water at the base of the plant to avoid wetting the leaves, which can increase the risk of fungal diseases in our low-humidity environment.

Signs of underwatering include wilting leaves and stunted growth. Overwatering, on the other hand, can lead to yellowing leaves and root rot. Applying a layer of mulch around your lemon balm plants helps retain moisture in the soil and suppress weeds.

Lemon balm is a vigorous grower and benefits from regular pruning to keep it tidy and productive. You can pinch off the tips of the stems throughout the growing season to encourage bushier growth. In midsummer, cut the plant back by about half to prevent it from becoming leggy and to stimulate new growth.

Be sure to remove flower stalks as they appear, unless you want the plant to self-seed. Lemon balm can be quite aggressive, so preventing it from flowering is a good way to keep it from spreading too much. As the first frost approaches in mid- November, you can cut the plant back to the ground. It will regrow in the spring.

You can start harvesting lemon balm leaves as soon as the plant is large enough, usually around mid May. The flavor is best before the plant flowers, so harvest frequently to encourage new growth and prevent flowering. Simply snip off the stems with scissors or pruning shears, taking care not to damage the plant.

Harvest in the morning, after the dew has dried, for the best flavor. Lemon balm is best used fresh, as it loses much of its flavor when dried. If you have a large harvest, consider making lemon balm tea, pesto, or infused oil. As the first frost approaches in mid- November, harvest any remaining leaves to use fresh or freeze for later use.

Here are a few common problems you might encounter with lemon balm in Northern California:

Aggressive Spreading

• What it looks like: Lemon balm popping up in unwanted areas of your garden.
• What causes it: Self-seeding and spreading through underground roots. In our mild climate, it has a long season to spread.
• How to fix/prevent it: Remove flower stalks before they set seed. Plant in a container or raised bed to contain the roots. Regularly pull up any unwanted seedlings.

Bolting

• What it looks like: The plant sends up a flower stalk prematurely, and the leaves become bitter or tough.
• What causes it: Heat stress, long days, or drought stress. Our summers can bring sudden heat spikes.
• How to fix/prevent it: Provide afternoon shade during the hottest part of the day. Keep the soil consistently moist. Harvest frequently to encourage new growth.

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. Although our humidity is low, microclimates can create pockets where powdery mildew thrives.
• How to fix/prevent it: Improve air circulation by spacing plants properly and pruning. Remove affected leaves. Apply neem oil or potassium bicarbonate spray.

Northern California Specific Challenges: Our moderate-to-hot, dry summers can stress lemon balm, making it more susceptible to bolting and powdery mildew. Consistent watering and providing afternoon shade are key to keeping your plants healthy and productive.

Lemon balm is a great companion plant for several vegetables in your Northern California garden. It repels certain pests and attracts beneficial insects.

Good companions include:

• Tomatoes: Lemon balm repels tomato hornworms and other pests.
• Squash: It attracts pollinators, which can improve squash yields.
• Broccoli and Cauliflower: Lemon balm can deter cabbage moths, which are a common pest of these brassicas.

Avoid planting lemon balm near rue, as it is said to inhibit its growth.