Lobelia in Zone 7A — Southeast

Lobelia, with its masses of tiny blue flowers, is a wonderful addition to any Southeast garden. It's perfect for adding a pop of color to borders, containers, or hanging baskets. Plus, it's relatively easy to grow and its spreading habit makes it ideal for filling in gaps in your landscape.

Our hot and humid summers here in Zone 7A can be tough on some plants, but Lobelia, with a little attention, can thrive. The long growing season, around 225 days, gives you plenty of time to enjoy these beautiful blooms, and starting seeds indoors at the right time avoids the worst of the early spring weather.

Starting Lobelia from seed indoors in our region can be a bit tricky due to their tiny size and slow growth. It's often easier to buy starts from a local nursery. However, if you're up for the challenge, aim to sow seeds late January through mid February, about 10 weeks before you plan to transplant them outdoors.

Use seed trays with a good seed-starting mix, and gently press the seeds into the surface – don't bury them. Keep the soil consistently moist by bottom watering to avoid disturbing the tiny seeds. Provide warmth and plenty of light, either from a sunny window or a grow light. Our springs here in the Southeast are fairly moderate, so you won't need to worry too much about temperature fluctuations.

Transplant your Lobelia seedlings outdoors early April through early May, once the danger of frost has passed. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sunlight and temperatures.

Space your plants 4-6 inches apart in a location that receives full sun to part shade. Be mindful of late frosts or unexpected temperature swings, which sometimes happen in early spring here. Given how small they are, it can honestly be easier to just buy starts from your local nursery.

Consistent moisture is key for Lobelia, especially in our hot and humid Southeast summers. They don't tolerate drought well and can go dormant if allowed to dry out completely. However, they usually rebound when the weather cools down.

During the active growing season, from spring through fall, check the soil moisture regularly. Stick your finger about 2 inches deep into the soil; if it feels dry, it's time to water. Aim for about 1 inch of water per week, either from rainfall or irrigation. Given our humidity, water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases.

Signs of underwatering include wilting leaves and dry soil. Overwatering can lead to yellowing leaves and potentially root rot. Mulching around your Lobelia plants with a layer of pine straw or shredded bark helps retain moisture and suppress weeds, which is especially helpful in our climate.

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

Simply use a pair of scissors or pruning shears to trim back the stems and foliage. Don't be afraid to be fairly aggressive – they'll bounce back quickly. As the first frost approaches around early November, you can let the plants go. They are annuals, so will not survive the winter.

Lobelia is grown for its ornamental value, so there's no need to harvest anything in the traditional sense. Just enjoy the masses of tiny blue flowers in your garden from mid June through late July. The plants bloom continuously throughout the growing season, adding a splash of color to your landscape.

Keep an eye on the plants and deadhead spent flowers to encourage more blooms. As the season winds down and the first frost approaches in early November, you can simply let the plants fade away. Enjoy them while they last, and look forward to planting them again next year.

Lobelia can face a few common problems in our Southeast gardens:

Dies back in extreme heat:

• What it looks like: The plant wilts, leaves turn brown and crispy, and growth slows or stops during the hottest part of the summer.
• What causes it: Our intense summer heat can stress Lobelia, especially if they aren't getting enough water.
• How to fix/prevent it: Provide afternoon shade during the hottest part of the day. Ensure consistent watering and consider mulching to help retain soil moisture.

Damping off from overwatering:

• What it looks like: Seedlings or young plants suddenly collapse and die, often with a white or gray mold at the base.
• What causes it: Overwatering creates a humid environment that encourages fungal growth, particularly in our already humid climate.
• How to fix/prevent it: Use well-draining soil, avoid overwatering, and provide good air circulation. Water in the morning so the soil surface can dry out during the day.

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.

Southeast Specific Challenges: Our hot and humid summers, combined with frequent afternoon thunderstorms, create ideal conditions for fungal diseases. Be vigilant about watering at the base of the plants, providing good air circulation, and using well-draining soil to help prevent problems. Additionally, our clay soil can retain too much moisture, so amending it with organic matter is crucial for healthy Lobelia growth.

Lobelia makes a great companion plant for several vegetables in the Southeast garden. Plant them near tomatoes and peppers to attract pollinators, which can boost fruit production. The bright blue flowers also complement the green foliage of lettuce, and Lobelia can act as a ground cover to help retain moisture in the soil.

Avoid planting Lobelia near aggressive plants that might compete for resources or shade them out. You don't want anything stealing its sunlight or hogging water.