How to Grow Lobelia from Seed in South Africa

Lobelia seed is extremely fine, and the difference between a flowering tray and an empty one is usually depth, temperature or moisture. This guide covers exactly four current GARDENING.co.za Lobelia erinus products: the compact, mounded Riviera Blue Eyes, Riviera Mix and Riviera White series selections, plus the spreading/trailing String Of Pearls Mix. It does not cover perennial cardinal flower or other Lobelia species.

Quick Grow Facts

Exact Varieties in This Guide

When to Sow Lobelia in South Africa

Treat Lobelia erinus as a cool-to-mild-season, frost-tender flowering annual. Adjust sowing to your region: choose a protected sowing period when a tray can remain near 21–22°C, then time planting out to avoid hard frost and extreme heat.

Winter-rainfall Western Cape

Sow under cover from late summer into autumn for a winter-to-spring display, or in late winter for spring colour. Protect shallow trays from driving rain and cold saturation. Plant in full winter sun or bright partial sun with free drainage; as late spring becomes hot and dry, give afternoon shade and never allow containers to dry completely.

Frost-prone interior

Sow in protected trays in late winter and plant out after the risk of hard frost. Autumn sowing is suitable only where seedlings and finished containers can be kept frost-free. Harden plants gradually to outdoor sun, wind and cooler nights. Frost-burned lobelia rarely makes a strong display, so replace badly damaged annual plants rather than forcing weak growth.

Humid coast and KZN Midlands

Use the coolest practical sowing window, usually autumn through the milder months. Give morning sun, bright afternoon shade, the widest listed spacing and strong airflow. Water the medium or soil early in the day without repeatedly wetting foliage. Avoid stagnant, enclosed positions where damping-off, Botrytis and root problems build quickly.

Hot-dry or subtropical interior

Grow lobelia through the mild season and avoid trying to establish it in peak summer heat. Use morning sun with afternoon shade, especially for containers and baskets. Keep the fine root zone evenly moist but drained; a single hot, dry afternoon can scorch a basket. Give Riviera light shade in hot weather and long late-spring days.

How to Sow the Fine Seed

1. Use a clean tray or plug cells and a fine, low-salt seedling medium around pH 5.8–6.2. Moisten it fully, let surplus water drain and level the surface before sowing.
2. For Riviera, place one intact pellet in each cell. Do not soak, split or crush it. For String Of Pearls, tap the fine raw seed sparingly from folded paper or mix a small measured portion with dry fine sand for more even distribution.
3. Press seed or pellet gently onto the surface for contact. Do not cover it with compost, vermiculite or sand. Sow as supplied without adding routine chilling or soaking.
4. Hold 21–22°C with bright filtered light and very even moisture. Pellets must stay moist enough for the coat to dissolve, while air remains in the medium. Bottom-watering or a very fine mist is safer than a stream that moves the seed.
5. Use a clear cover only to steady humidity, never to create saturated conditions. Vent it daily and remove it as soon as emergence begins.
6. Do not discard a sound tray early: controlled-production intervals are not guaranteed home emergence deadlines. Maintain steady moisture and temperature while checking for emergence.

Back to growing instructions

Light, Moisture and Seedling Care

After emergence, give bright light immediately and begin lowering humidity. Keep the medium evenly moist, not continuously wet. Seedlings that stay warm, dark and saturated stretch or collapse. Feed only after true leaves develop, using a weak, balanced seedling feed; excess salts and nitrogen damage the tiny roots and make soft growth. Good air movement is important, but do not point a drying fan directly at uncovered seedlings.

Transplanting and Spacing

Allow about four to five weeks for the plug stage. Transplant when true leaves can be handled and the roots hold the small plug together. Lift by a leaf or the root ball, never by the thin stem. Keep seedlings from a pellet together when transplanting. Prick out raw String Of Pearls seedlings as small, manageable clumps rather than tearing apart every thread-like plant.

Harden plants for roughly a week by gradually increasing outdoor light and air while protecting them from frost, harsh wind and hot afternoon sun. Plant at the same depth as the plug. Use 20–25 cm centres for Riviera and about 25 cm for String Of Pearls. The lower end of the Riviera spacing range makes a quicker solid edge, while 25 cm improves airflow in humid gardens.

Ongoing Care and Flowering

Use fertile, humus-rich soil that holds steady moisture but drains freely. In mild weather, full sun supports dense growth and flowers; in hot regions, morning sun or bright partial shade preserves the display. Water at soil level whenever the upper surface begins to dry. Baskets and small pots need more frequent checks than beds. Feed containers lightly and regularly, but stop increasing nitrogen if foliage becomes soft and flowering drops.

Riviera naturally makes a compact mound and normally needs no pinching. String Of Pearls should be allowed to spread or trail. After a heavy flush, trim tired stems lightly and water well to encourage renewed growth; do not cut a heat-stressed or frost-damaged plant hard. Flowering time varies with temperature, light and establishment. Riviera is bred for early flowering, and Riviera flowering can be delayed by daylengths shorter than 12 hours, although excessive late-spring heat can shorten the display.

Why Germination or Establishment Fails

• Nothing emerges: the seed was buried under a covering layer of mix, the surface dried, the tray was too cool or hot, or the seed is no longer viable. Surface-sow a small control at 21–22°C.
• Pellets stay hard: humidity or contact moisture was too low. Re-moisten gently without flooding; do not crush the coat.
• Raw seed forms one dense patch: too much String Of Pearls seed was tipped into one place. Thin early or lift small clumps; do not attempt to separate every microscopic seedling.
• Seedlings collapse at soil level: damping-off follows dirty containers, stagnant humidity and saturated medium. Improve hygiene, ventilation and drainage, and remove affected plants.
• Seedlings are pale and stretched: light is too weak, temperature is too high after emergence, or nitrogen is excessive. Increase bright light gradually and feed less.
• Plants wilt or stop flowering in heat: the fine roots dried or hot afternoon sun exceeded the plant's cool-season tolerance. Rehydrate slowly, provide afternoon shade and move containers out of reflected heat.
• Leaves or crowns rot on the humid coast: plants are crowded, foliage stays wet overnight or drainage is poor. Use 25 cm spacing, early-day soil-level watering and better airflow.
• Growth blackens after a cold night: lobelia is frost-tender. Protect containers and delay planting in frost-prone areas.

Inspect soft growth for aphids, mites, thrips, slugs and snails. Correct crowding, moisture and airflow first. If a pesticide or fungicide is needed, use only a product registered in South Africa for the crop and problem, and follow its label exactly.

Shop the Lobelia in This Guide

• Lobelia Riviera Blue Eyes Seeds
• Lobelia Riviera Mix Seeds
• Lobelia Riviera White Seeds
• Lobelia String Of Pearls Mix Seeds