Sweet alyssum (Lobularia maritime or Alyssum maritimum) is a woody stemmed perennial that spreads and forms mats, making it a good ground cover. It is originally from Europe and western Asia. Sweet alyssum rarely gets more than nine inches high. It can, however, grow as tall as a foot and spread as far as a foot. The leaves are narrow and have whitish hairs on them. The flowers are white or pinkish, small, honey-scented, and form dense clusters at the end of the stems. Sweet alyssum flowers in the summer and continues flowering until mid-autumn. Sweet alyssum is easy to start and will flower even if planted as late as July.
This plant needs full sun to grow best. Sweet alyssum performs best in cool weather. In hot climates, some afternoon shade is appreciated.
Sweet alyssum is aggressive but not invasive. This means it will spread in your flower bed or rock garden as far as it can but will not escape the garden and become a pest. It is also deer resistant. Butterflies are attracted by its sweet scent and nectar.
Keep the soil moist around your sweet alyssum but not soggy. Soggy soil can lead to rhizoctonia root and stem rot.
Sweet alyssum is generally treated as an annual when growing it, even though it is really a perennial. It will self seed every year once established. To do that, seeds should be sowed indoors six to eight weeks before the last frost. Do not cover the seeds as they need sunlight to germinate. They will germinate when the temperature is 65 to 70 degrees F. It takes the new plant around fourteen days to appear. Before planting the sweet alyssum in your flower bed, you need to harden off the plants.
To harden off your transplants, place them outside in a sheltered place for one or two hours, then bring them back in. Gradually, over a week’s time, leave the plants outside until they are outside all day.
After your plants are hardened off, plant one sweet alyssum every twelve inches in your garden bed. Water in well.
You can direct seed sweet alyssum in your flower bed after all danger of frost has passed. Again, do not cover the seeds as they need light to germinate. They will start to emerge after two weeks or so. Be sure to keep the flower bed moist but not soggy during this period.
Sweet alyssum does not need much maintenance. After the first bloom fades, shear off the stems to cause a second bloom.
Leaf hoppers and whitefly are both pests of sweet alyssum. To control leaf hoppers, you can introduce beneficial insects such as lady beetles, lacewings, and minute pirate bugs. They all love the egg and larvae stage of the leaf hoppers. Insecticidal soap will kill the adults. Be sure to cover the underside of the leaves when spraying to get the leaf hoppers where they live.
Insecticidal soap will also kill whitefly. The same beneficial insects you use to get rid of leaf hoppers will eat whitefly eggs and larvae.