Lemon Balm in Zone 10A — Southern California

Lemon Balm is a fantastic addition to any Southern California garden. Its bright, lemony flavor is perfect for teas, salads, and even adding a refreshing zing to your water during those long, hot summer days inland. Plus, the satisfaction of harvesting fresh herbs year-round in our mild climate is hard to beat.

While we enjoy a long growing season, we also face challenges like drought and occasional extreme heat. Luckily, with careful planning and attention to watering, you can easily incorporate Lemon Balm into your garden and enjoy a bountiful harvest throughout our 349-day growing season.

Starting Lemon Balm indoors isn't strictly necessary in our climate, but it can give you a head start, especially if you're aiming for an early harvest. Starting seeds indoors from late November through mid December, about six weeks before transplanting, will allow you to get a jump on the season.

Use seed trays with a good seed-starting mix and provide warmth and light. Bottom watering is ideal for seedlings to prevent damping off – just set the tray in a shallow dish of water until the soil surface is moist. Given our very-early spring character, a little indoor prep can make a difference.

Transplant your Lemon Balm seedlings outdoors from mid January through mid February. This gives them time to establish before the summer heat inland kicks in.

Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. Plant them 18-24 inches apart in a sunny or partially shaded spot. Keep an eye on the forecast – we can sometimes get unexpected cold snaps that time of year, so be prepared to cover them if necessary.

Direct sowing Lemon Balm is a simple and effective method in Southern California, thanks to our long growing season. You can direct sow from mid January through early October, giving you a wide window of opportunity.

Prepare the soil by loosening it and removing any weeds. Sow seeds directly into the soil, lightly cover them, and keep them consistently moist until they germinate. Thin seedlings to 18-24 inches apart once they emerge. Direct sowing is less work than starting indoors, but your harvest might be a bit later.

Lemon Balm prefers moderate watering, which is important to keep in mind, especially with our water restrictions here in Southern California. While it's more tolerant of moisture than some other herbs, it's not drought-tolerant.

During the cooler months, when we get some winter-wet rainfall, you might only need to supplement with watering once a week, if at all. In the summer heat inland, especially during Santa Ana winds, you'll likely need to water deeply two or three times a week. Use the "finger test" – 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, adjusting based on rainfall and temperature. Water at the base of the plant to avoid creating humid conditions that can lead to powdery mildew.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot. Applying a layer of mulch around the base of the plant helps retain moisture and regulate soil temperature, which is especially useful during our hot summers.

Pruning Lemon Balm is fairly straightforward and helps keep it productive. In midsummer, when the plant might start to look a little leggy, cut it back by about half to encourage bushier growth.

Regularly remove any flower stalks to prevent self-seeding, as Lemon Balm can be quite aggressive. Towards the end of the season, as our first frost approaches around late December, you can give it a final trim to tidy it up, but don't cut it back too severely.

You can expect your first harvest of Lemon Balm about 70 days after planting, typically from late March through early January in our zone. Look for healthy, vibrant leaves that are free from blemishes.

The best flavor comes from leaves harvested before the plant flowers. To harvest, simply snip off the stems with scissors or pruning shears, taking care not to damage the main plant. Regular harvesting encourages continued production. As late December approaches, harvest as much as you can before any potential frost.

Here are some common problems you might encounter with Lemon Balm in Southern California:

Aggressive Spreading

• What it looks like: Lemon Balm popping up in unwanted areas of your garden.
• What causes it: Lemon Balm spreads easily via seeds and roots.
• How to fix/prevent it: Remove flower stalks before they go to seed. Consider growing it in a container to contain its spread. 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: Bolting is often triggered by heat or drought stress, both common occurrences in our summer heat inland.
• How to fix/prevent it: Plant in a location with partial shade to protect it from the hottest afternoon sun. Keep the soil consistently moist. Remove flower stalks as soon as you see them to encourage leaf production.

Powdery Mildew

• What it looks like: A white or grayish powdery coating on the leaves and stems.
• What causes it: Powdery mildew thrives in warm days, cool nights, and moderate humidity. Despite our generally low-to-moderate humidity, coastal influence can still create favorable conditions.
• How to fix/prevent it: Improve air circulation by spacing plants adequately and pruning. Remove affected leaves promptly. Apply neem oil or potassium bicarbonate sprays. A milk spray (1 part milk to 9 parts water) can also be effective.

Southern California Specific Challenges: Our hot summers and potential for drought mean that Lemon Balm can be susceptible to bolting and drying out if not properly watered and shaded. The Santa Ana winds can also quickly dehydrate plants, so keep a close eye on moisture levels during those periods.

Lemon Balm can be a beneficial companion plant in your Southern California garden. It's said to repel certain pests and attract pollinators.

Good companions include tomatoes, squash, broccoli, and cauliflower. Lemon Balm may help repel tomato hornworms and cabbage moths, protecting your tomatoes and brassicas. It also attracts beneficial insects that can help pollinate your squash. There aren't any significant bad companions to be aware of, so you can generally plant it freely among your other garden vegetables.