Lobelia in Zone 10A — Desert Southwest

Lobelia, with its profusion of tiny blue flowers, brings a refreshing splash of color to our Desert Southwest gardens. It's perfect for edging borders, filling containers, or cascading from hanging baskets. The best part is that you can enjoy its beauty in both spring and fall here.

Even with our extreme heat and arid conditions, growing Lobelia is achievable thanks to our two distinct growing seasons. By timing your planting right, you can enjoy these beauties during the cooler months. With a 339-day growing season, we have plenty of time to make it work.

Starting Lobelia indoors in the Desert Southwest is possible, but given the tiny seeds and slow initial growth, many gardeners here opt for buying starts. If you're feeling ambitious, start your seeds indoors from mid-November through early December, about 10 weeks before you plan to transplant.

Use seed trays with a good seed-starting mix and provide warmth and light. Bottom watering is especially helpful for these tiny seeds to prevent disturbing them. Remember that our spring comes very early here, so timing is crucial.

Transplant your Lobelia seedlings outdoors from early February through early March. Before transplanting, harden them off for about a week by gradually exposing them to outdoor conditions.

Space them 4-6 inches apart in well-draining soil. Keep an eye on the weather; even though it's typically mild, we can still get unexpected temperature dips during this time. Given the tiny seeds and slow growth, buying established starts from a local nursery might be the easiest route.

Watering Lobelia correctly is crucial for success in our arid Desert Southwest climate. These plants prefer consistently moist soil and are not drought-tolerant.

During the spring and fall growing seasons, aim to water deeply 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, Lobelia often goes dormant, so reduce watering but don't let the soil completely dry out. Monsoon moisture can help but is often unpredictable.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our sometimes humid monsoon season. Signs of underwatering include wilting and dry, crispy leaves. Overwatering can lead to root rot, indicated by yellowing leaves and a soggy soil. A layer of organic mulch, like compost, helps retain moisture and regulate soil temperature.

Lobelia requires minimal pruning, but a little attention goes a long way. When flowering slows down in midsummer due to the heat, shear the plants back by about half.

This encourages fresh growth and a second flush of blooms when cooler weather arrives in the fall. Remove any dead or yellowing foliage to keep the plants tidy. As the first frost approaches in late December, you can let the plants die back naturally or trim them up for a tidier winter appearance.

Lobelia is primarily grown for its ornamental value, so there's no "harvest" in the traditional sense. Enjoy the masses of tiny blue flowers from early April through late May.

Deadheading spent blooms can encourage continued flowering throughout the season. Simply pinch off the faded flower spikes to keep the plants looking their best. As the first frost approaches in late December, the plants will naturally decline, signaling the end of their blooming season.

Here are some common problems you might encounter with Lobelia in the Desert Southwest:

Dies back in extreme heat

• What it looks like: The plant wilts, leaves turn brown and crispy, and overall growth stalls or declines during the hottest part of summer.
• What causes it: Lobelia struggles with our extreme heat and intense sun. The plants can't transpire fast enough to stay cool, leading to heat stress and dieback.
• How to fix/prevent it: Provide afternoon shade with shade cloth, especially during the hottest months. Ensure adequate watering, but avoid overwatering. Mulch around the base of the plant to help retain soil moisture and keep the roots cool. Consider moving container plants to a cooler location during the peak of summer.

Damping off from overwatering

• What it looks like: Seedlings suddenly collapse and die, often with a slimy or water-soaked appearance at the base of the stem.
• What causes it: Damping off is a fungal disease that thrives in overly moist conditions. It's especially problematic when starting seeds indoors.
• How to fix/prevent it: Use a sterile seed-starting mix and avoid overwatering. Ensure good air circulation around seedlings. Bottom watering can help prevent the soil surface from staying too wet. If damping off occurs, remove affected seedlings immediately to prevent the spread of the disease.

Slugs

• What it looks like: Irregular holes in leaves, especially on low-growing plants. Silvery slime trails on leaves and soil. Damage is often worse at night and in wet weather.
• What causes it: Slugs are gastropods that feed at night in moist conditions. They hide under mulch, boards, and debris during the day.
• How to fix/prevent it: Use beer traps (shallow dish of beer sunk into soil). Apply iron phosphate bait (pet-safe). Remove hiding spots like mulch, boards, and debris. Water in the morning so the soil surface dries by evening. Consider using copper tape around beds or applying diatomaceous earth around plants.

Desert Southwest Specific Challenges: The extreme heat and arid humidity of the Desert Southwest can be tough on Lobelia. While monsoon rainfall can be a welcome relief, it can also create conditions that favor fungal diseases and slug infestations. Providing shade, ensuring proper watering, and monitoring for pests and diseases are essential for growing healthy Lobelia here.

Lobelia makes a great companion plant for several vegetables in the Desert Southwest garden. Planting it near tomatoes and peppers can attract beneficial insects that help with pollination and pest control.

It also works well with lettuce, providing ground cover that helps retain moisture in our dry climate and keeps the soil cooler for the lettuce roots. Avoid planting Lobelia near plants that prefer very dry conditions, as its moderate watering needs might create an environment that's too moist for them.