How to Grow Alyssum from Seed in South Africa
Sweet alyssum is a low, fragrant bedding plant for edging, pots, hanging baskets and pollinator-friendly garden gaps. This guide is scoped only to the four active GARDENING.co.za seed products verified below. All four are Lobularia maritima (historically sold as Alyssum maritimum), but their seed forms and mature growth forms differ.
Quick Grow Facts
| Product | Seed form | Depth and light | Germination | Spacing | Growth form |
|---|---|---|---|---|---|
| Clear Crystal® Mixture | Coated | Fine cover, maximum 1 mm; breeder says cover; light not required in Stage 1 | Packet 8–10 days; controlled breeder range can begin in 3–4 days at 21–22°C | 15 cm dense edging; 20–25 cm for fuller mounds | Mounded, 15–25 cm high and 30–36 cm wide |
| Clear Crystal® White | Coated | Fine cover, maximum 1 mm; breeder says cover; light not required in Stage 1 | Packet 8–10 days; controlled breeder range can begin in 3–4 days at 21–22°C | 15 cm dense edging; 20–25 cm for fuller mounds | Mounded, 15–25 cm high and 30–36 cm wide |
| Snow Cloth | Raw | Surface press or the thinnest cover, never deeper than the packet's 1 mm; keep in bright ambient light | Packet 8–10 days; allow about 5–14 days in ordinary home conditions | 15 cm dense carpet; 20–30 cm for separate mounds | Low, spreading white carpet, about 12–20 cm high |
| Snow Crystals | Raw | Fine light cover, maximum 1 mm; breeder lists Stage 1 light as optional | Packet 8–10 days; controlled breeder range can begin in 3–4 days at 21–22°C | 15 cm dense carpet; 30–40 cm for a full trailing plant | Spreading and trailing, 15–25 cm high and 30–36 cm wide |
- Botanical name: Lobularia maritima; Alyssum maritimum is a historical synonym.
- Position: Full sun in cool to mild weather; light afternoon shade helps in very hot districts.
- Best sowing window: Cool to mild regional windows. “Year round” on the packet is possible only where heat, frost, moisture and humidity are controlled.
- Flowering: Packet timing is about 8–10 weeks from sowing under favourable conditions. Heat, cold, low light or moisture stress can delay or interrupt bloom.
- Use: Ornamental edging, beds, rockeries, containers, hanging baskets and low pollinator planting.
Fine Seed Depth and Light: Do Not Bury Alyssum
The four packet labels state 1 mm. Treat that as a maximum fine cover, not a target burial depth. A heavy 1 mm crust of compact soil can block tiny seedlings. Use fine seedling mix or fine vermiculite, keep the cover loose and maintain even moisture from below or with a gentle mist.
Depth and light are not identical across these products. PanAmerican Seed says the coated Clear Crystal series should be covered and does not require light in Stage 1. Its single coated seed should be multiple-sown at five to six seeds per cell; the breeder's thick-vermiculite instruction applies to the separately sold multi-seed pellet form, not these GARDENING.co.za single coated-seed variants. Snow Crystals receives a light cover with optional Stage 1 light. For raw Snow Cloth, surface pressing under bright ambient light is safe where moisture can be held, or use only the thinnest cover up to the packet's 1 mm.
How to Sow Sweet Alyssum Seed
- Fill a clean tray or small cells with fine, free-draining seedling mix. Pre-moisten it and let surplus water drain.
- Sow the matching seed form. Use five to six coated Clear Crystal seeds or five to six raw Snow Crystals seeds per cell. Sow a small pinch of Snow Cloth for a transplantable clump.
- Apply the exact shallow cover in the table. Never compact the surface or bury the seed below 1 mm.
- Keep the mix evenly moist and aerated. Coated seed must become fully wet, but the cell must not stand in water.
- Aim for about 18–22°C. Clear Crystal and Snow Crystals breeder culture uses 21–22°C for Stage 1; Snow Cloth also germinates across a cooler 12–21°C home range.
- Give bright light immediately after emergence and lower humidity gradually. Weak light makes the tiny seedlings stretch.
Direct sow or trays? Direct sow into fine, settled soil during cool, reliable weather for informal carpets. Tray sowing gives better moisture control, protects costly coated seed and makes it easier to transplant small clumps. Do not try to separate every seedling in a clump.
Transplanting, Thinning and Hardening Off
Move clumps once they have several true leaves and the roots hold the plug together, usually about four weeks after emergence for the named breeder lines. Water first, lift by the plug rather than the stems and plant at the same depth. Harden seedlings over 5–7 days by increasing outdoor light and air movement while protecting them from hard frost, hot wind and driving rain.
Thin direct-sown plants early enough that remaining roots are not torn. Use the closer spacing for a quick dense edge and the wider spacing when you want each mound or trailing plant to reach its natural spread.
When to Sow Alyssum in South Africa
Winter-rainfall Western Cape
Sow from March to May for winter and spring colour, or again from August to September where irrigation is reliable. Protect trays from driving rain and give good airflow through wet spells. Plants in full sun flower best in cool weather; light afternoon shade and regular water help a late planting as summer approaches.
Eastern Cape Coast and Garden Route
Sow from late summer through autumn, or in late winter to spring. Use raised, free-draining soil in rainy districts and shelter small seedlings from coastal wind. Treat colder inland Eastern Cape gardens like the frost-prone interior.
Highveld, Gauteng, Free State, North West and Inland Mpumalanga
Sow from February to April for winter and spring colour where plants can be protected from hard frost, or sow from August to October after the worst freezes. Sweet alyssum tolerates cool weather and light frost better than heat, but tiny seedlings still need protection from severe frost and dry winter wind.
KwaZulu-Natal Coast
Autumn to early winter and late winter to early spring are the most reliable windows. Avoid the hottest, most humid part of summer. Use morning sun, light afternoon shade, wide spacing and early-day watering so foliage dries before night.
KwaZulu-Natal Midlands and Higher Inland Gardens
Sow in early autumn or from late winter into spring. Protect young plants from hard frost, persistent mist and saturated soil. Full sun is useful in cool conditions, but airflow and drainage are as important as temperature.
Lowveld, Limpopo and Hot Mpumalanga Districts
Sow from March to May and again from July to September. Establish plants before severe heat, give morning sun with light afternoon shade and never let containers bake dry. Flowering may pause in hot weather and resume after trimming when nights cool.
Northern Cape and Dry Inland Districts
Use late winter to early spring or an autumn window while nights are mild. Prepare irrigation before sowing and shelter trays from desiccating wind. A gravel mulch can reduce splash after establishment, but keep it away from tiny crowns.
Clear Crystal® Mixture: Mounded Mixed Colour
This product is coated Lobularia maritima Clear Crystal® Mixture, a tetraploid PanAmerican Seed series. Sow five to six coated seeds per cell, cover finely to a maximum 1 mm and keep the coating continuously moist without saturating the mix. Breeder culture uses 21–22°C and can reach maximum germination in 3–4 days; the current packet gives the more practical 8–10-day home window.
Space 15 cm apart for dense edging or 20–25 cm for fuller mounds. Plants are about 15–25 cm high and 30–36 cm wide, with fragrant, larger flowers and stronger container performance than standard diploid alyssums. The mixture contains separately coloured plants; one seed does not produce a multicoloured plant.
Clear Crystal® White: Controlled White Mounds
This coated Clear Crystal® White has the same sowing method as the Mixture: five to six coated seeds per cell, fine cover no deeper than 1 mm, 21–22°C and continuous moisture around the coating. Light is not required in Stage 1, but bright light is essential immediately after emergence.
Use 15 cm spacing for a quick white edge or 20–25 cm for separate mounds. Expect plants about 15–25 cm high and 30–36 cm wide, with fragrant large white blooms and a more controlled mounded form than Snow Crystals.
Snow Cloth: Low White Carpet
Snow Cloth is a raw-seed, low-spreading white Lobularia maritima cultivar rather than the Clear Crystal series. Press a small pinch onto the moist surface and either leave it exposed under bright ambient light where moisture can be maintained or apply only the thinnest cover, never deeper than the current packet's 1 mm. Aim for about 12–21°C and allow roughly 5–14 days; the current packet states 8–10 days.
Space clumps 15 cm apart for a fast carpet or 20–30 cm apart for distinct mounds. Expect a low, fragrant white groundcover about 12–20 cm high, useful beside paths, in containers and as low living mulch where competition and self-sowing are acceptable.
Snow Crystals: Vigorous Trailing White
Snow Crystals is a raw-seed tetraploid cultivar with extra-large pure-white fragrant flowers, vigorous growth and better heat tolerance than standard diploids. Multiple-sow five to six seeds per cell, apply a fine light cover up to 1 mm and keep at 21–22°C. Breeder culture lists Stage 1 light as optional and 3–4 controlled days; the current packet gives 8–10 days for home sowing.
Plant 15 cm apart for a dense carpet or 30–40 cm apart when each spreading or trailing plant should develop fully. Expect about 15–25 cm height and 30–36 cm spread. It suits beds, larger pots and container edges where its looser trailing form has room.
Soil, Water, Feeding and Flowering
- Soil: Use moderately fertile, well-drained soil or container mix. Heavy, saturated soil causes crown and root loss.
- Water: Keep seedlings evenly moist. Established plants tolerate short dry periods, but continuous flowering needs steady water; let surplus drain.
- Feeding: Feed lightly after establishment. Excess nitrogen produces soft leaves and fewer flowers. Avoid strong fertiliser on tiny seedlings.
- Airflow: Do not crowd humid plantings. Water at soil level early in the day and remove dead material.
- Flowers: Expect the first useful display in about 8–10 weeks under favourable conditions. Shear plants back by about one-third to one-half after a flush or when heat opens the centre; water, then allow cooler weather to drive fresh bloom.
Why Alyssum Germination or Establishment Fails
- No emergence: the seed was buried too deeply, the fine surface dried, temperature was outside the useful range or the packet was old.
- Coated seed stays hard: the coating never became fully wet. Re-wet gently and evenly without flooding the cell.
- Seed rots: the mix stayed saturated and airless, or trays stood in water. Use a clean porous medium and drain after every watering.
- Seedlings stretch: light was too weak after emergence. Move them into brighter conditions gradually and improve airflow.
- Clumps collapse: damping off, downy mildew or crown rot is favoured by crowding, wet foliage and poor drainage. Remove badly affected plants and clean trays.
- Leaves yellow but growth is soft: roots are too wet or nitrogen is excessive. Correct drainage before feeding.
- Flowering stops in heat: trim lightly, maintain root-zone moisture and wait for cooler nights; use afternoon shade in the hottest districts.
- Plants fail after transplanting: clumps were pulled apart, roots dried or plants were moved straight into frost, hot sun or wind without hardening.
Pests, Disease and Safe Use
Watch young plants for slugs, snails, flea beetles and aphids. Downy mildew and damping off are the main wet-condition risks. Improve drainage, airflow and hygiene first; use only controls registered for the crop and your region, exactly as labelled.
These products are sold as ornamental seed, not food seed. Do not eat seed or seed coating. Do not assume flowers are food-safe when plants may have received ornamental-crop treatments; keep packets and seed away from children and pets.