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Sweet Alyssum Care

Lobularia maritima or sweet alyssum, a plant species from the Brassicaceae family is native to Europe. Lobularia, in Greek means ‘small pod’, about the fruit shape, and Maritima, or the species name refers to its native coastal habitat, from sea level up to altitudes of 1000 feet.

These annual plants make a colorful carpet of tiny flowers that are utilized to blanket gardens or landscapes. This low-growing plant grows rapidly and can cover the ground within 2 months of being planted. Its narrow leaves are gray-green, slightly hairy, and lance-shaped. It grows 3–9 inches high and 6–12 inches wide.

The stem is branched and produces dense clusters of tiny flowers, the flowers are around 0.20 inches in diameter, with a honey-like fragrance, and have four rounded petals four sepals, six stamens with yellow anthers with petal colors of white, pink, red, yellow, violet, or lilac. The flowers bloom throughout their growing season, or all-year-round in temperate climates free from frost and are insect-pollinated. The fruits are oval to rounded elongated hairy seed pods with two seeds. Seeds are usually dispersed by wind or fall off by themselves.

They are easy to propagate from seed and can be started in early spring once winter has passed. In climates free from frost or snow, these plants can be grown all through the year. Most varieties tend to wilt and fade in hot weather but will bloom again in autumn. They are heat and drought-resistant. Plants with dark-colored flowers grow better in cool temperatures. These plants are considered to be invasive in California and tend to grow aggressively in other areas of the US due to their ability to self-sow.

These plants can be grown under taller plants like a living mulch or grown along garden edges or to fill empty spaces along walkways and walls. They also grow nicely in containers or hanging baskets.

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Sunlight

These plants love full sunlight but prefer some afternoon shade in hot and dry climates. However, they can develop blight or rot under too much shade as this prevents the soil and leaves from drying out completely. Ideally, plant them where they can get 6 or 8 hours of daily sunlight.

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Water

Water them once a week, with more frequent watering in hot weather. Ensure that water drains away and that the soil drains well since the plant can get root rot easily. If you’re growing them in stony soil, water them twice weekly.

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Humidity

If growing them under high humidity, you can reduce watering to prevent rot.

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Temperature

These plants can grow throughout the year in temperate climates, preferring temperatures below 85°F, with a minimum of 20°F. As mentioned, they can tolerate higher temperatures although flowering may slow down and resume when the weather turns cooler.

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Soil

They like moist soil that drains well although they are tolerant of different types of soil, even beaches, and dunes. The plants will not do well in water-logged soil.

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Repotting

They grow well in well-draining containers. When repotting, choose a new container about 7 inches deep, fill it with well-draining soil, and dig a hole to place the root ball in. Insert the root ball, filling in empty spaces with soil. The soil must be around two inches lower than the container’s rim. Water well when done.

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Propagation

These plants are easy to grow from harvested seeds, although you will have to purchase seeds for hybrid varieties. Scatter seeds on top of well-draining soil incorporated with slow-release fertilizer and press down lightly to ensure good contact with the soil. Don’t cover the seeds as they should be kept exposed to light. Keep watering the soil until germination. Go back to your usual watering plan when the seedlings appear.

Additional Care

Plants growing in the garden typically don’t need feeding while plants growing in containers need monthly feeding with a liquid balanced fertilizer. Avoid over-feeding as this can result in more foliage and reduced flowering.

Deadhead old flowers to keep the plants flowering continuously and help set new buds. However, if the plants cover a wide area, it would be easier to cut them down by one-third instead of deadheading. After some time, the plants will become gangly and leggy, so pruning is necessary to keep them looking neat.

In cold climates, cut the plants down in winter and protect them with frost cloth. You could also simply leave them alone since they are prolific self-seeders. After winter is done, you can cut away dead foliage to make space for the seeds from the previous season to start sprouting.

Common Problems

These plants are favored by beneficial insects like butterflies, bees, and others and rarely get bothered by insect pests. However, insects like cyclamen mites or bagrada bugs can infest the plants under adverse conditions. To avoid harming beneficial insects, spray the plants using diluted neem oil or insecticidal soap in the mornings or afternoons to avoid the sun’s intensity.

Bagrada bugs are more difficult to eradicate and usually have to be manually picked away. If there is a substantial infestation, simply remove the plant to prevent its spread. 

Powdery mildew or Botrytis blight can also affect these plants in cool, damp climates. Treat the plants with fungicide and avoid over-watering as this also leads to clubroot or swollen roots that will prevent water absorption. 

As mentioned, these plants generally don’t tolerate very hot weather and tend to wilt. If you have planted them in soil that drains well, you can increase your watering frequency. Wilted plants can be pruned down by one-third and fed with a water-soluble fertilizer to help encourage new growth.

Hot temperature, disease, transplant shock, under-watering, and lack of nutrients can also make the leaves turn yellow – examine the plant to identify the cause. One leaf or several leaves is a warning and, while not automatically a death sentence, the underlying cause should be identified and treated to prevent losing the entire plant. 

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