Lobelia in Zone 3A — Mountain West

Lobelia, with its masses of vibrant blue flowers, is a fantastic addition to any Mountain West garden. It thrives in our intense sunlight and offers a welcome splash of color, especially useful for filling in gaps around taller plants. Plus, the cool nights we often have, even in summer, seem to intensify the flower color, making them even more stunning.

Growing Lobelia in our Zone 3A Mountain climate requires a bit of planning due to our short 96-day growing season and potential for late frosts. But by starting seeds indoors at the right time, or buying starts, you can absolutely enjoy these beauties in your garden from midsummer right up until our first frosts arrive in early September.

Starting Lobelia from seed indoors is optional, but can give you a head start if you want a specific variety. Begin in late March through mid April, about 10 weeks before you plan to transplant outdoors. The seeds are tiny, so sow them very shallowly in seed trays filled with a good quality seed starting mix.

Keep the soil consistently moist by bottom watering – setting the tray in a shallow dish of water until the surface of the soil is damp. Provide warmth with a heat mat and plenty of light, either from a grow light or a very sunny window. Our late spring can be deceiving, so don't rush things; patience is key in high altitude gardening.

Transplant your Lobelia seedlings outdoors around mid June, after all 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 our intense UV and fluctuating temperatures.

Space plants 4-6 inches apart in a location that receives full sun to partial shade. Honestly, given our short season, you might have the best luck just buying starts from a local nursery. Lobelia seeds are tiny, and they grow slowly, so a purchased transplant will give you a jump on the season.

Consistent moisture is crucial for Lobelia to thrive in our dry Mountain West climate. Aim to keep the soil consistently moist, but not waterlogged, throughout the growing season. The finger test is your friend: stick your finger about two inches into the soil; if it feels dry, it's time to water.

In general, during the peak of summer, your Lobelia might need about an inch of water per week, either from rainfall or supplemental watering. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases, even in our low humidity. Signs of underwatering include wilting leaves and dry, crispy edges. Overwatering can lead to yellowing leaves and root rot.

Mulching around your Lobelia plants with a layer of organic material, like compost or shredded bark, helps retain soil moisture and regulate soil temperature, which is especially important given our cool nights.

Lobelia requires minimal pruning, but a little attention can encourage more blooms. When flowering starts to slow down in midsummer – often in late July or early August – shear the plants back by about half. This stimulates fresh growth and a new flush of flowers as temperatures cool off again in late summer and early fall.

Simply use a pair of scissors or pruning shears to trim back the entire plant, removing spent flowers and any leggy growth. Don't be afraid to be a bit aggressive; Lobelia is resilient and will bounce back quickly. As our first frosts approach in early September, you can let the plants go and allow them to set seed, or simply remove them from the garden.

Lobelia is primarily grown for its beautiful flowers, so there's no real "harvest" in the traditional sense. However, you can enjoy the masses of tiny blue flowers from mid August through early September, or whenever your transplants start blooming. The blooms are continuous, so you'll have color for weeks.

Simply enjoy the blooms in your garden! To encourage continued production, deadhead spent flowers regularly by pinching or trimming them off. This prevents the plant from putting energy into seed production and encourages more flowers.

As the first frost approaches in early September, there's no need to do anything special. The frost will likely kill the plants, but they may self-seed if you leave the spent flowers in place.

Here are some common problems you might encounter with Lobelia in our Mountain West gardens:

Dies back in extreme heat

• What it looks like: The plant wilts, leaves turn brown and crispy, and flowering stops.
• What causes it: Even though our summers are moderate-at-altitude, Lobelia can suffer during brief periods of intense heat, especially when combined with our low humidity.
• How to fix/prevent it: Provide afternoon shade during the hottest part of the day. Water deeply and regularly to keep the soil consistently moist. Mulch around the plants to help retain soil moisture and keep the roots cool.

Damping off from overwatering

• What it looks like: Seedlings suddenly collapse and die. Stems may appear thin and water-soaked at the base.
• What causes it: Overwatering, especially in cool, poorly ventilated conditions, encourages fungal growth that attacks young seedlings.
• How to fix/prevent it: Use a well-draining seed starting mix. Avoid overwatering by bottom watering. Provide good air circulation. Sterilize seed trays before use.

Slugs

• What it looks like: Irregular holes in leaves, especially on low-growing plants. Silvery slime trails on leaves and soil. Damage is 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. Water in the morning so the soil surface dries by evening. Consider copper tape around beds or diatomaceous earth around plants.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity can be a double-edged sword for Lobelia. While the cool nights enhance the flower color, the dry air means you need to be vigilant about watering. The intense sun can also stress the plants, so providing some afternoon shade is often beneficial.

Lobelia makes a great companion plant for several vegetables in our Mountain West gardens. Planting it near tomatoes and peppers can attract beneficial insects that help control pests. The Lobelia also provides ground cover, helping to retain soil moisture and suppress weeds, which is especially helpful given our dry conditions.

Lobelia also pairs well with lettuce, providing shade and cooling the soil, which can help prevent bolting in hot weather. Avoid planting Lobelia near anything that requires very dry soil, as its need for consistent moisture could create an unfavorable environment for those plants.