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
| Product group | Seed form | Depth, temperature and time | Spacing and flowering outcome |
|---|---|---|---|
| Riviera Blue Eyes, Mix and White | Current Gardening variants and labels: pelleted seed. The breeder also offers Riviera as multi-seed pellets or raw seed; the purchased packet controls. Do not crush a pellet. | Surface-sow; do not cover. Keep at 21–22°C and evenly moist. The packet allows 14–21 days at home; the breeder records 4–5 days from 50% to maximum germination under controlled production. | 20–25 cm; current packets say 25 × 25 cm. Compact, ball-shaped, mounded plants about 13 cm high and 20 cm wide, with early blue-and-white, mixed or white flowers. |
| String Of Pearls Mix | Current Gardening variants and label: very fine raw seed sold by weight. Sow sparingly; no pellet coat is present. | Surface-sow; do not cover. Keep at 21–22°C and evenly moist. The packet allows 14–21 days at home; the breeder table gives 4–6 controlled days. | About 25 cm apart. A spreading/trailing annual with mixed light and deep blue, violet, white and related shades, some with white eyes; suited to edges, containers and baskets. |
Exact Varieties in This Guide
Riviera Blue Eyes — compact, mounded
Lobelia Riviera Blue Eyes Seeds produces sapphire-blue flowers with clear white centres. The current Gardening sale variants are pelleted. Sow one intact pellet as one sowing unit; the current label does not confirm how many seeds are inside each pellet. Expect the Riviera series' compact, ball-shaped growth form at about 13 cm high and 20 cm wide, using 20–25 cm final spacing.
Riviera Mix — compact, mounded colour mix
Lobelia Riviera Mix Seeds is the pelleted mixed-colour member of the same early Riviera series. Its propagation, 13 cm height, 20 cm spread and 20–25 cm spacing match the other Riviera products. The mix describes flower colour, not a mixture of species or growing methods.
Riviera White — compact, mounded white
Lobelia Riviera White Seeds produces clean white flowers on the same compact Riviera growth form. The current variants are pelleted. Give white lobelia the same light and airflow as the coloured selections; shade that is too deep reduces flowering and damp, crowded foliage encourages disease.
String Of Pearls Mix — spreading/trailing raw seed
Lobelia String Of Pearls Mix Seeds is different from Riviera: the current variants are fine raw seed sold in 1 g and 4 g packs, and the mature growth form spreads or trails rather than staying in a tight ball. The accepted cultivar profile describes mixed light and deep blue, purple and white flowers, some with white eyes, on plants that can reach about 25 cm high. Use it at the front of beds, over container edges or in baskets, with about 25 cm between planting centres.
When to Sow Lobelia in South Africa
Treat Lobelia erinus as a cool-to-mild-season, frost-tender flowering annual. The packet's broad “Spring to Autumn” line is not equally suitable in every 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. Light shading is specifically recommended by the Riviera breeder in hot weather and long late-spring days.
How to Sow the Fine Seed
- 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.
- 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.
- Press seed or pellet gently onto the surface for contact. Do not cover it with compost, vermiculite or sand. No chilling, soaking or other pretreatment is required.
- 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.
- Use a clear cover only to steady humidity, never to create saturated conditions. Vent it daily and remove it as soon as emergence begins.
- The current packet window is 14–21 days at home. Do not discard a sound tray early, and do not compare that window directly with the breeder's shorter controlled-production interval.
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
Riviera breeder production allows 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 unless the purchased packet explicitly says otherwise. 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 packet's 25 × 25 cm works for all four products; the lower end of the Riviera breeder 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. The current packets give 12–16 weeks to bloom. Riviera is bred for early flowering, and lobelia flowers more freely once days exceed about 12 hours, although excessive late-spring heat can shorten the display.
Why Germination or Establishment Fails
- Nothing emerges: the seed was buried under the packet's conflicting 2 mm instruction, 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.