Lemon Balm in Zone 9B — Southern California

Lemon Balm is a fantastic addition to any Southern California garden. Its lemony fragrance and flavor enhance teas, salads, and even desserts, and you can harvest almost year-round. Plus, growing your own herbs provides a satisfaction you just can't get from store-bought ones, especially when you're enjoying a homegrown herbal tea on a mild SoCal evening.

We definitely face challenges here in SoCal, from drought to the occasional heat wave, but with a long growing season of 334 days and mild winters, Lemon Balm thrives with a little planning. You'll find that the timing recommendations here help you navigate those potential problems and enjoy a bountiful harvest.

Starting Lemon Balm indoors gives you a head start, but it's honestly not always necessary here in Southern California, given our long growing season. If you're aiming for a particularly early harvest or want more control over germination, it's a fine option.

If you choose to start indoors, sow seeds early to late December, about six weeks before you'd like to transplant them outdoors. Use seed trays or small pots filled with a good seed-starting mix. Keep them consistently moist – bottom watering works great to prevent damping-off – and provide warmth and light, either with a heat mat and grow lights or a sunny windowsill. Remember, our spring comes very early in SoCal, so getting a jump start can be beneficial.

Transplant your Lemon Balm seedlings outdoors late January through late 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. Choose a spot with full sun to partial shade, and space the plants 18-24 inches apart. Keep in mind that we can still get some surprising temperature dips during this time of year, so be prepared to cover your young plants if a cold snap is predicted.

Direct sowing Lemon Balm is a simple and effective method here in Southern California, thanks to our mild climate. You can sow seeds directly into the garden late January through early October.

Prepare the soil by loosening it and amending with compost. Lemon Balm prefers a soil temperature of around 70°F for optimal germination. Sow seeds shallowly and keep the soil consistently moist until seedlings emerge. Thin seedlings to 18-24 inches apart once they are a few inches tall. The advantage of direct sowing is avoiding transplant shock, but the downside is less control over germination and early growth.

Lemon Balm needs moderate watering to thrive in our Southern California climate. While it's not drought-tolerant, it tolerates more moisture than many other herbs.

During the cooler months (late fall, winter, early spring), when we get some rainfall, you may only need to water once or twice a week, depending on how much rain we've had. In the hotter summer months, especially if you're inland, you'll likely need to water every other day, or even daily during extreme heat waves. Use the "finger test" – stick your finger about 2 inches into the soil. If it feels dry, it's time to water. Aim for about 1 inch of water per week, adjusting based on weather conditions.

Water at the base of the plant to avoid wetting the leaves, which can increase the risk of fungal diseases, even with our low-to-moderate humidity. 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 your plants helps retain moisture and regulate soil temperature, which is especially important during our hot summers.

Lemon Balm benefits from minimal pruning to keep it healthy and productive. It can get a bit leggy if left unmanaged.

In midsummer, cut back the plant by about half to encourage bushier growth and prevent it from becoming too sprawling. Regularly remove any flower stalks that appear, as this prevents the plant from self-seeding aggressively throughout your garden. As the first frost approaches in late December, you can give the plant a final trim, but don't cut it back too hard. Leave some foliage to protect the crown during the mild winter.

You can start harvesting Lemon Balm leaves as early as early April, about 70 days after planting, and continue harvesting through early January. The flavor is best before the plant flowers, so harvest frequently to encourage leaf production.

To harvest, simply snip off individual leaves or small stems with scissors or pruning shears. Avoid taking more than one-third of the plant at a time to ensure continued production. Lemon Balm is best used fresh, as it loses much of its flavor when dried. However, you can preserve it by freezing or infusing it in oil or vinegar. As the first frost approaches in late December, harvest any remaining leaves to use fresh or preserve for later.

Here are three 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 through seeds and rhizomes. In our mild climate, it can become quite invasive if not contained.
• How to fix/prevent it: Plant Lemon Balm in a container to restrict its spread. Remove flower stalks before they go to seed. Regularly pull up any unwanted seedlings.

Bolting

• What it looks like: The plant sends up a flower stalk prematurely. The leaves become bitter and tough.
• What causes it: Bolting is triggered by heat and drought stress. Our summer heat inland can definitely cause this.
• How to fix/prevent it: Provide afternoon shade during the hottest months. Keep the soil consistently moist. Regularly harvest leaves to delay bolting.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves and stems. Leaves may curl, yellow, and die.
• What causes it: Powdery mildew thrives in warm days, cool nights, and moderate humidity. While we don't have high humidity, the coastal influence can still create favorable conditions.
• How to fix/prevent it: Improve air circulation by spacing plants properly. Remove affected leaves. 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: The hot heat inland can stress Lemon Balm, making it more susceptible to bolting and powdery mildew. Our drought conditions and water restrictions mean you need to be mindful of watering, but avoid letting the plant dry out completely.

Lemon Balm makes a great companion plant for several vegetables in your Southern California garden.

Good companions:

• Tomatoes: Lemon Balm repels tomato hornworms and other pests that can damage tomato plants.
• Squash: It can deter squash bugs and vine borers.
• Broccoli and Cauliflower: Lemon Balm can help repel cabbage moths and other pests that target these brassicas.

I wouldn't recommend planting it near anything that needs very dry soil since Lemon Balm prefers moderate moisture.