Germination temperature
About 24 °C (75 °F) is ideal; seed-starting charts use up to 26-28 °C (78-82 °F).
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Sweet alyssum is one of the quickest annuals from seed: it needs light to germinate and flowers about 6-8 weeks after sowing. This guide covers shallow sowing, the cool season it prefers, and how to keep it flowering when the weather turns hot.
About 24 °C (75 °F) is ideal; seed-starting charts use up to 26-28 °C (78-82 °F).
On the surface or barely covered; do not bury the seed.
2-4 days in a warm, humid propagation space; up to about 2 weeks in ordinary conditions.
Light helps germination, so keep the seed at the surface.
None needed.
Both work. Sow a small pinch of seeds per cell or spot rather than single seeds.
Alyssum seed is very small. Sow it dry, and mix it with a little fine sand if you scatter it over a bed or border edge so it spreads thinly.
Not needed. The seed takes up water easily without nicking or rubbing.
Not needed. Alyssum has no cold requirement and germinates as soon as it is warm and moist.
Not needed, and soaked seed is tiny and hard to handle. Water the surface gently after sowing instead.
Professional growers germinate alyssum at about 24 °C (75 °F) with high humidity. The University of Alaska seed-starting chart uses 26-28 °C (78-82 °F). In a mild season it will also come up outdoors, just more slowly.
Press the seed onto the surface or cover it with only a dusting of fine compost or vermiculite. Extension services advise barely covering it because light helps it germinate.
A fine, well-drained seed compost. Alyssum is prone to damping off, so avoid heavy, waterlogged mixes and old, dirty trays.
Keep the surface evenly moist but not wet. Mist or water from below rather than flooding the tray, which washes the small seeds together.
Leave the seed exposed to light. Deep sowing is the most common reason for a patchy stand.
Roots and seed leaves can appear in 2-4 days at about 24 °C (75 °F). In the Alaska chart, germination took 8-15 days, so allow about two weeks before resowing.
Start seed indoors about 5-8 weeks before you want to plant out. Breeders sow 3-5 seeds per plug and grow them on as one clump; do not separate them. Harden transplants off before planting.
Grow seedlings cool: professional culture uses about 10-13 °C (50-55 °F) at night and 13-16 °C (55-60 °F) by day. Warmer temperatures make the shoots stretch.
Plants reach about 8-25 cm (3-10 in) tall and spread 15-30 cm (6-12 in), so give each clump room. Flowering begins about 6-8 weeks after sowing.
Cause: seed buried too deep, or the surface dried out. Fix: sow on the surface, cover only with a dusting of vermiculite, and keep the tray covered or misted until germination.
Cause: damping off in wet, poorly drained compost. Fix: use fresh, free-draining seed compost, water from below and give good air movement.
Cause: seed-grown alyssum slows down and can stop flowering in summer heat. Fix: give afternoon shade in hot climates, shear plants back lightly, water and feed lightly; they recover when it cools.
Cause: downy mildew, stem rot or crown rot in crowded, wet plantings. Fix: improve drainage, avoid overhead watering in the evening, and do not crowd plants.
Alyssum flowers best in cool weather. In the Indian plains grow it as a winter annual, sown as the monsoon ends and nights start to cool. In the hills, where summers are mild, sow it in spring for flowers through summer.
Average, well-drained soil is enough. Rich soil and heavy feeding give leafy plants with fewer flowers.
When plants look leggy or carry more seed pods than flowers, shear them back lightly. Deadheading or shearing increases flowering.
Alyssum flowers attract beneficial insects that help control aphids, so it is a useful edging for vegetable beds.
Choose a colour mix or Royal Carpet alyssum for fragrant edging, pots and hanging baskets.
Only very lightly. Light helps alyssum germinate, so press the seed onto the surface or give it a dusting of vermiculite to keep it moist.
Seed-grown alyssum often pauses in hot weather. Shear the plants back, water and feed them lightly, and they usually flower again when temperatures fall.
Yes. It is one of the easiest annuals to direct sow. Scatter the seed thinly on a fine, moist surface, press it in, and keep it moist until the seedlings appear.