Lobelia in Zone 7B — Desert Southwest

Lobelia is a fantastic addition to any desert garden, adding a splash of vibrant blue that thrives in our unique climate. The cascading habit of these flowers makes them perfect for hanging baskets, rock gardens, or spilling over the edges of containers, bringing a touch of cool color to your landscape.

While the Desert Southwest presents challenges like extreme heat and low humidity, Lobelia can flourish with proper care and timing. Our long 245-day growing season gives you ample opportunity to enjoy these beauties in spring and fall, bookending the intense summer heat.

Starting Lobelia from seed indoors is possible but requires patience. Begin in mid January through early February, about 10 weeks before you plan to transplant. Use seed trays with a good seed-starting mix, providing warmth and bright light – a grow light works wonders in our region, especially with our very-early spring start.

Keep the soil consistently moist but not soggy; bottom watering is an excellent way to prevent damping-off. Remember, Lobelia seeds are tiny and slow to grow, so many of us desert gardeners find it easier to purchase established transplants from a local nursery.

Transplant your Lobelia seedlings outdoors in late March through late April, once the danger of frost has passed. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them acclimate to our intense sunlight and temperature fluctuations.

Space plants 4-6 inches apart in well-draining soil. Be mindful of late-season temperature swings that can damage young plants. If you're using transplants, handle them gently as they can be delicate.

Consistent moisture is key for Lobelia survival in our arid Desert Southwest climate. Unlike some of our more drought-tolerant natives, Lobelia needs regular watering to thrive. During the hot spring and fall growing seasons, check the soil moisture daily, using the "finger test" – if the top 2 inches feel dry, it's time to water.

Aim for about 1 inch of water per week, adjusting as needed based on rainfall (especially during monsoon season) and temperature. Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our warm, arid environment. Signs of underwatering include wilting and dry, crispy leaves, while overwatering can lead to yellowing leaves and root rot.

A layer of organic mulch, like shredded bark or compost, can help retain soil moisture and regulate soil temperature, providing a much-needed buffer against our extreme heat. Remember, Lobelia is not drought-tolerant and will likely go dormant if allowed to dry out for too long. But don't worry, they often bounce back when the weather cools!

Lobelia requires minimal pruning, but a little attention can keep them looking their best. When flowering slows down in midsummer due to the extreme heat, shear back the plants by about half. This encourages fresh growth and a second flush of blooms when the weather cools down in the fall.

Simply use sharp scissors or pruning shears to trim back the stems, removing any spent flowers or yellowing foliage. As the first frost approaches around mid- November, you can let the plants die back naturally, or trim them down for a tidier appearance.

Since Lobelia is grown for its beautiful blooms, there's no real "harvest" in the traditional sense. You'll see the first masses of tiny blue flowers sometime in early June through late July, about 65 days after transplanting. Enjoy the continuous display of color in your garden.

Deadheading (removing spent flowers) isn't necessary, as the plants naturally produce new blooms throughout the growing season. Simply appreciate the vibrant blue flowers as they cascade from your containers or garden beds. As the first frost approaches in mid- November, the plants will naturally fade, marking the end of their season.

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

Dies back in extreme heat

• What it looks like: The plant stops flowering and begins to wilt, even with regular watering. Leaves may turn brown and crispy.
• What causes it: Our extreme summer heat stresses the plants, causing them to go dormant as a survival mechanism.
• How to fix/prevent it: Provide afternoon shade with shade cloth or plant in a location that receives morning sun only. Ensure consistent moisture and good air circulation. Don't be alarmed; they often revive when temperatures cool down in the fall.

Damping off from overwatering

• What it looks like: Seedlings suddenly collapse and die, often with a fuzzy, mold-like growth at the base of the stem.
• What causes it: Overwatering creates a damp environment that encourages fungal diseases, especially when starting seeds indoors.
• How to fix/prevent it: Use a well-draining seed-starting mix and avoid overwatering. Provide good air circulation and consider bottom watering to keep the foliage dry.

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 create unique challenges for growing Lobelia. The key is to provide consistent moisture, afternoon shade, and good air circulation to help these delicate plants thrive in our demanding climate.

Lobelia makes a great companion plant for several vegetables in the Desert Southwest garden. Plant them near tomatoes and peppers; their delicate flowers attract pollinators, which can improve fruit set. The shade provided by taller tomato plants can also offer some protection from our intense sun.

Lettuce also benefits from being planted near Lobelia. The Lobelia can act as a ground cover, helping to retain moisture in the soil and suppress weeds, which is especially helpful during our hot, dry spring and fall growing seasons. Avoid planting Lobelia near plants that prefer very dry conditions, as their need for consistent moisture can create an unsuitable environment for drought-tolerant species.