Lobelia in Zone 9B — Desert Southwest

Lobelia, with its masses of tiny blue flowers, is a delightful addition to any Desert Southwest garden. It's perfect for adding a touch of cool color to borders, containers, or hanging baskets. These plants are easy to enjoy as flowers.

Our extreme heat and arid conditions can be tough, but with careful timing, Lobelia can thrive during our two growing seasons. Starting indoors at the right time and paying close attention to watering will set you up for success. With a 313-day growing season, you have plenty of opportunity to enjoy these beauties.

Starting Lobelia from seed indoors is an option, but be warned: the seeds are tiny, and the seedlings are slow to grow. Honestly, you might find it easier to buy starts from a local nursery. But if you're up for the challenge...

Start your seeds indoors in early to late December, about 10 weeks before you want to transplant them outside. Use seed trays and a good seed-starting mix. Keep the soil consistently moist, and provide warmth and plenty of light. Bottom watering can help prevent damping off. Remember, our very-early spring means you need to get a head start indoors.

Transplant your Lobelia seedlings outdoors from mid February through mid March. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the Desert Southwest's intense sunlight and temperature fluctuations.

Space the plants 4-6 inches apart in well-draining soil. Even though we're past the typical frost date, keep an eye on the forecast for any unexpected cold snaps. Buying starts is smart, given how delicate these plants are, and how many our region looses.

Lobelia needs consistent moisture to thrive, which can be tricky in our arid Desert Southwest climate. Aim to keep the soil consistently moist, but not soggy. These plants are NOT drought-tolerant and will quickly suffer if allowed to dry out.

During the spring and fall growing seasons, water deeply about 2-3 times per week, providing about 1 inch of water each time. Use the "finger test" – stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. During the monsoon season, adjust your watering schedule based on rainfall. In the extreme heat of summer, Lobelia may go dormant if stressed, but will return when the weather cools down.

Water at the base of the plant to avoid wetting the foliage, which can increase the risk of fungal diseases. Signs of underwatering include wilting leaves and dry soil. Overwatering can lead to root rot, so watch for yellowing leaves and soggy soil. Mulching around the base of the plants can help retain moisture and regulate soil temperature.

Lobelia requires minimal pruning, but a little maintenance can keep them looking their best. When flowering slows down in midsummer, shear back the plants by about half. This encourages fresh growth and a new flush of flowers in the cooler fall weather.

Simply use sharp scissors or pruning shears to trim back the stems. Don't be afraid to be a little aggressive – Lobelia is resilient and will bounce back quickly. As the first frost approaches in mid- December, you can let the plants die back naturally.

Lobelia is grown for its beautiful flowers, not for edible parts, so there's no traditional harvest. The "harvest" is enjoying the masses of tiny blue flowers in your garden!

Expect the first flush of blooms in late April through mid June, about 65 days after transplanting. To encourage continued production, deadhead spent flowers regularly. Simply pinch or snip off the faded blooms just below the flower head.

As the weather cools in the fall, you can expect another round of blooms. As the first frost approaches in mid- December, simply enjoy the last of the flowers before the plants die back for the season.

Lobelia can face a few challenges in the Desert Southwest:

Dies back in extreme heat

• What it looks like: Wilting, browning, and eventual death of the plant during the hottest part of the summer.
• What causes it: The extreme heat of our summers can stress Lobelia, especially when combined with low humidity.
• How to fix/prevent it: Provide afternoon shade with shade cloth. Ensure adequate watering. Mulch around the base of the plant to keep the soil cooler. Consider moving container plants to a cooler location during the hottest months.

Damping off from overwatering

• What it looks like: Seedlings suddenly collapse and die, often with a white, fuzzy mold visible on the soil surface.
• What causes it: Overwatering creates a favorable environment for fungal pathogens that attack young seedlings.
• How to fix/prevent it: Use a well-draining seed-starting mix. Water from the bottom to avoid wetting the foliage. Ensure good air circulation. Avoid overwatering.

Slugs

• What it looks like: Irregular holes in leaves, especially low-growing plants. Silvery slime trails on leaves and soil. Damage worse at night and in wet weather.
• What causes it: Gastropods that feed at night in moist conditions. Hide under mulch, boards, and debris during the day.
• How to fix/prevent it: Beer traps (shallow dish of beer sunk into soil). Iron phosphate bait (pet-safe). Remove hiding spots. Water in morning so soil surface dries by evening. Copper tape around beds. Diatomaceous earth around plants.

Desert Southwest Specific Challenges: The extreme heat, arid humidity, and occasional monsoon rainfall of the Desert Southwest can make growing Lobelia a challenge. Consistent watering, afternoon shade, and well-draining soil are essential for success.

Lobelia makes a great companion plant for many vegetables and herbs in the Desert Southwest. Planting them near tomatoes and peppers can help attract pollinators, leading to better fruit set. The flowers also attract beneficial insects that prey on common garden pests.

Lobelia also pairs well with lettuce, providing shade and helping to keep the soil cool and moist. Avoid planting Lobelia near aggressive plants that might outcompete them for water and nutrients.