Lobelia in Zone 7A — Desert Southwest

Lobelia's profuse blooms of vibrant blue make it a welcome sight in our Desert Southwest gardens. This plant's delicate beauty belies its resilience, providing a burst of color during our milder seasons. It's perfect for adding a touch of cottage charm to containers or edging beds, and the cool blue hues offer a visual respite from our sun-baked landscapes.

Desert gardening presents unique challenges, but Lobelia can thrive here with careful attention to timing and watering. Our 230-day growing season gives you two opportunities to enjoy this beauty – spring and fall – if you avoid planting during the extreme heat of summer.

Starting Lobelia from seed indoors is possible, but given the tiny size of the seeds and the plant's slow initial growth, it's often more practical to buy established starts. If you're feeling ambitious, begin in late January through mid February, about 10 weeks before you plan to transplant.

Use seed trays with a fine-grained seed starting mix. Keep the soil consistently moist by bottom watering – setting the tray in a shallow container of water until the surface is damp. Provide warmth and plenty of light, as our very-early spring means these seedlings need a head start.

Transplant your Lobelia outdoors in early April through early May, after the last threat of frost has passed. Before planting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This prevents shock and ensures they adjust to our intense sunlight.

Space plants 4-6 inches apart in well-draining soil. Keep a close eye on the weather forecast during this period; temperature swings are common, and a late cold snap can damage tender transplants. Given the tiny seeds and slow growth, many Desert SW gardeners opt to purchase established transplants.

Watering is crucial for Lobelia's summer survival in our arid climate. This plant needs consistent moisture and doesn't tolerate drought, but avoid waterlogged soil, which can lead to root rot.

During the spring and fall growing seasons, aim to water deeply about twice a week, providing roughly 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 monsoon season, adjust your watering schedule based on rainfall, but remember that our alkaline soil drains quickly.

In the extreme heat of summer, Lobelia may go dormant. Reduce watering but don't let the soil dry out completely. Water at the base of the plant to avoid wetting the foliage, as our arid conditions still allow for some fungal issues if leaves stay wet. Signs of underwatering include wilting and browning leaf edges; overwatering can cause yellowing leaves and mushy stems. Applying a layer of organic mulch, such as shredded bark, helps retain moisture and regulate soil temperature.

Lobelia requires minimal pruning, but a little attention can keep it looking its best. When flowering slows down in midsummer due to the extreme heat, shear the plants back by about half.

This encourages fresh growth and a second flush of blooms when temperatures cool in the fall. Simply use sharp scissors or pruning shears to trim the foliage, leaving healthy growth intact. As the first frost approaches in early November, you can let the plants die back naturally.

Lobelia isn't typically harvested for consumption; it's grown for its ornamental value. Expect masses of tiny blue flowers from mid June through late July, adding a splash of color to your garden.

Enjoy the blooms as they appear, and deadhead spent flowers to encourage continuous production. Simply pinch off the faded blooms just below the flower head. As the season winds down and temperatures drop, the plant will naturally slow its flowering. There's no need to harvest anything before the first frost in early November; simply enjoy the display while it lasts.

Lobelia can face a few challenges in our Desert Southwest climate. Here are the most common problems and how to address them:

Dies back in extreme heat

• What it looks like: The plant wilts, leaves turn brown and crispy, and overall growth stops.
• What causes it: Our extreme heat and intense sun can overwhelm Lobelia, especially if it's not adequately watered.
• How to fix/prevent it: Provide afternoon shade with shade cloth, water deeply and regularly, and consider moving container plants to a cooler location during the hottest months.

Damping off from overwatering

• What it looks like: Seedlings or young plants suddenly collapse and die, often with a fuzzy, mold-like growth at the base.
• What causes it: Overwatering creates a favorable environment for fungal pathogens, especially in poorly draining soil.
• How to fix/prevent it: Use well-draining soil, avoid overwatering, and ensure good air circulation. Bottom watering seedlings can also help.

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: These gastropods feed at night in moist conditions. They 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 all affect Lobelia. The extreme heat can cause the plants to go dormant or even die back completely. Low humidity means you need to be diligent about watering, but monsoon moisture can create conditions favorable for fungal diseases.

Lobelia benefits from companion planting in the Desert Southwest. Plant it near tomatoes and peppers. The Lobelia attracts beneficial insects that help pollinate these crops. It can also be planted with lettuce, where it acts as a ground cover to keep the soil cool and moist.

Avoid planting Lobelia near aggressive plants that will compete for water and nutrients. These plants will quickly overwhelm the Lobelia.