How to grow Sweet Alyssum

Where to plant

Grow sweet alyssum along bed edges, between stepping stones, under roses and among vegetables, or spilling from pots and hanging baskets. It grows well in full sun where summers are cool, and does better with some afternoon shade where they are hot. It needs average, well drained soil, and a bed that is too rich gives leaves at the expense of flowers.

Timing follows the heat. In Florida, the Gulf South, Texas, the desert and Southern California, sow from fall into late winter for flowers through the cool months. In the Mid-South and Mid-Atlantic, sow in late winter to spring and again in late summer for fall. In the Northeast, Midwest, Mountain West, Northern Plains and Alaska, sow or plant out in spring for flowers from early summer until hard frost.

• In coastal California, sweet alyssum has escaped from gardens into dunes, bluffs and coastal scrub, and the California Invasive Plant Council rates it as a limited invader. Near wild coastal land, shear it before it sets seed.

Choosing a variety

Seed grown types such as Carpet of Snow make a low, white, strongly scented mat. White forms tend to be the most vigorous and fragrant, while pink, rose and purple seed mixes are a little less robust. Sterile hybrids sold as plants, such as Snow Princess and the Stream series, are bigger (up to about a foot tall and 2 to 3 feet across), handle summer heat much better and keep flowering through summer in the South. They do not set seed, so they are only sold as plants.

How to plant

1. Sow directly where the plants are to grow, or start seed indoors 6 to 8 weeks before planting out.
2. Press the tiny seed onto the surface or cover it with only a dusting of soil, since it needs light to germinate.
3. Keep the surface moist until seedlings appear, usually within one to two weeks.
4. Thin or plant out hardened seedlings about 8 inches (20 cm) apart. Hardened plants can go out a week or two before the last frost.
5. Do not crowd the plants. Dense, wet growth can rot.

Watering and feeding

Sweet alyssum tolerates a short dry spell but flowers best with steady moisture, so water when the top inch of soil dries, especially in pots and baskets. Water at the base in the morning so the foliage dries quickly.

Feed lightly. Extension sources differ: Clemson suggests a monthly all purpose fertilizer through the growing season, while the University of Wisconsin warns that rich soil gives foliage instead of flowers. A light feed in pots and little or none in garden beds is a sensible middle course.

Pruning and care through the year

• When flowering slows in summer heat or the plants are leggy and full of seed pods, shear them back by about a third. They regrow and flower again when the weather cools.
• Sweet alyssum reseeds, though not aggressively. Seedlings from named varieties usually come up white and a little taller than the parent.
• In the South, plants often fade in the summer heat. Pull them out and sow again in fall.

Flowers and cutting back

Sweet alyssum is grown for its flowers and the beneficial insects they feed rather than for picking. A short shear after each flush keeps it tidy and flowering. The small sprigs can go into posies, and the scent is strongest in the evening.

Growing in pots

Alyssum is a classic filler for pots, window boxes and hanging baskets, where it spills over the edge. Use a good potting mix and a pot with drainage holes, and water more often than in the ground, as small pots dry quickly in warm weather.