Lemon Balm in Zone 9B — Desert Southwest

Lemon balm is a fantastic addition to any Desert Southwest garden. Its lemony flavor brightens teas and dishes, and it's incredibly satisfying to harvest fresh herbs right from your own yard. Plus, in our climate, it's a perennial that can provide years of enjoyment.

Desert gardening has its challenges, with our extreme heat and alkaline soil. But with careful timing around our two growing seasons and a little extra attention to watering, you can successfully grow lemon balm here. Our long, 313-day growing season gives you plenty of time.

Starting lemon balm indoors is an option, giving you a head start on the growing season, especially if you want a larger, more established plant right away. Sow seeds indoors from mid-December through early January, about six weeks before our last frost. This is also useful if you want to get a head start on planting before the very-early spring.

Use seed trays with a good seed-starting mix. Keep them warm (around 70°F) and provide plenty of light – a grow light works wonders. Don't forget to water from the bottom to avoid damping off.

Transplant your lemon balm seedlings outdoors from early February through early March, after the last expected frost. Be sure to harden them off first by gradually exposing them to outdoor conditions for about a week. This prevents transplant shock from the temperature swing.

Space them 18-24 inches apart to allow for their mature size. Keep an eye on the weather; those early weeks can still bring unexpected dips in temperature, so be prepared to cover them if needed.

Direct sowing lemon balm is easy, especially if you want a more naturalized look in your garden. Sow seeds from early February through late September, taking advantage of our two growing seasons. You have about a 3-week window.

Prepare the soil by loosening it and amending with compost to improve drainage and fertility. Lemon balm needs temperatures around 60-70°F to germinate, so time your sowing accordingly. Thin seedlings to 18-24 inches apart once they emerge.

Lemon balm needs consistent moisture, especially in our arid Desert Southwest climate. While it can tolerate more moisture than other herbs, it's not drought-tolerant. Finding the right balance is key for summer survival.

During our active growing seasons (spring and fall), water deeply about 2-3 times per week, providing about 1 inch of water each time. Use the "finger test" – if the top 2 inches of soil feel dry, it's time to water. During the extreme heat of summer, you might need to water daily, especially if your lemon balm is in full sun. Reduce watering to once a week or less during the cooler winter months, depending on rainfall.

Water at the base of the plant to avoid wetting the leaves, which can encourage fungal diseases in our monsoon season. Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to root rot, indicated by yellowing leaves and a mushy stem base. A layer of mulch around your lemon balm helps retain moisture and regulate soil temperature, especially important in our harsh climate.

Lemon balm is a pretty low-maintenance plant, but a little pruning helps keep it healthy and productive. In midsummer, when the extreme heat can stress the plant, cut it back by about half to prevent it from getting leggy. This also encourages new, bushier growth.

Remove any flower stalks as they appear, unless you want it to self-seed (it can be aggressive!). As our first frost approaches in mid- December, give your lemon balm a final light trim to remove any dead or damaged foliage. This prepares it for winter dormancy.

You can start harvesting lemon balm leaves about 70 days after planting, typically from mid-April through late December in our region. Look for healthy, green leaves that are at least a few inches long. The flavor is best before the plant flowers.

Harvest by snipping off the top few inches of the stems, taking care not to remove more than one-third of the plant at a time. This encourages continued production. Throughout the season, regular harvesting encourages bushier growth and prevents the plant from becoming too leggy. As the first frost approaches in mid- December, harvest any remaining leaves to dry or freeze for later use.

Lemon balm is generally easy to grow, but here are a few common problems to watch out for in the Desert Southwest:

Aggressive Spreading

• What it looks like: Lemon balm pops up in unwanted areas of your garden, spreading beyond its intended space.
• What causes it: Lemon balm readily self-seeds, and its roots can also spread. This is made worse by our long growing season, where seeds have plenty of time to mature and sprout.
• How to fix/prevent it: Remove flower stalks before they go to seed. Consider growing lemon balm 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. Leaves become bitter or tough.
• What causes it: Bolting is triggered by heat stress, especially in our extreme summer heat. Drought stress can also contribute.
• How to fix/prevent it: Provide afternoon shade during the hottest part of the day. Ensure consistent watering to prevent drought stress. Harvest leaves regularly to encourage continued vegetative growth.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems, and sometimes fruit. Leaves curl, yellow, and die.
• What causes it: Powdery mildew thrives in warm days, cool nights, and moderate humidity. It's more common during our monsoon season, although the dry leaf surfaces in our arid climate are also favorable to it.
• How to fix/prevent it: Improve air circulation by spacing plants adequately and pruning dense growth. Remove and dispose of affected leaves. Apply neem oil or potassium bicarbonate sprays.

Desert Southwest Specific Challenges: Our extreme heat and low humidity can stress lemon balm, making it more susceptible to bolting and powdery mildew. Consistent watering and providing afternoon shade are crucial for summer survival. The monsoon season can increase the risk of powdery mildew, so good air circulation and preventative treatments are essential.

Lemon balm makes a great companion plant for several vegetables in the Desert Southwest garden. It helps repel pests from tomatoes and squash. Plant near broccoli and cauliflower to deter cabbage moths.

Avoid planting lemon balm near rue, as it can inhibit its growth.