Growing Sweet Alyssum
Sweet alyssum makes a colorful carpet of tiny flowers that you can use to blanket your garden or landscape. Native to Europe, the low-growing foliage grows quickly, covering the ground with tiny cross-shaped, four-petal flowers within two months of being sown from seed. Its gray-green leaves are slightly hairy, narrow, and lance-shaped.
Easy to grow from plant or seed, sweet alyssum is a cool-season flower that can be set out in early spring once all danger of frost has passed (in frost-free climates, sweet alyssum can also be grown throughout the fall and winter). Most varieties will fade in the heat but bloom again in the fall. It is an invasive plant in California and can grow aggressively in other parts of the U.S.
Sweet alyssum is nearly unmatched for ease of care. It tolerates cool temperatures, may slow flowering during summer’s heat, but bursts into bloom again when temperatures cool. The flowers have a lively, honey-like fragrance and are related to cabbage and mustard. They will self-sow and provide bright colors year after year in milder climates. Sweet alyssum is generally problem-free, although aphids will arrive on the scene when the plant’s under stress.
As sweet alyssum plants spread, they create a living mulch under taller plants. Use sweet alyssum along edges in the garden or fill nooks and crannies on walkways and walls. The tight, free-flowering plants are also great “spillers” for hanging baskets and containers.
Sweet alyssum loves full sun, but it does not like prolonged dry periods. If your region is sweltering and dry, an area with afternoon shade will work best for this plant, though you should remember that it can get stem rot or leaf blight if too much shade prevents the leaves and soil from completely drying out. Aim to plant your sweet alyssum somewhere where it can get six to eight hours of sunlight a day.
Sweet alyssum plants prefer soil that is moist and well-draining. They’re tolerant of many different planting locations and on sandy beaches and dunes. It can also grow on cultivated fields, walls, slopes, and even in cracks in sidewalks or walls. The plants will do poorly in boggy soil or where drainage is problematic.
Provide your sweet alyssum plants with at least an inch of water every week, watering them more frequently during hot weather days or dry spells. The water should drain well. Otherwise, the plant is susceptible to root rot. If you plant your sweet alyssum in a stony landscape (or anywhere that dries out quickly), provide extra water.
Temperature and Humidity
Gardeners can grow sweet alyssum in temperate weather all year long, although the plants are short-lived. Typically, they are vigorous self-seeders, however, hybrid varieties may not look like the parent plant. So, it may seem that the same plants are surviving all year long; the reality is that new seedlings are filling in. Although many varieties may stop flowering in heat, sweet alyssum plants repeat bloom. They will likely pick up again in the fall. In high humidity, compensate by reducing the amount of water given to plants.
Typically, in-ground sweet alyssum plants do not need fertilizer unless the soil is poor. Plants grown in containers will need monthly feedings using a water-soluble, well-balanced fertilizer. When starting seeds, add a time-release fertilizer to the soil at planting. When blooms are spent, apply again to stimulate new growth. Too much fertilizer can cause lush foliage and reduced blooms.
Deadheading sweet alyssum will keep the plants flowering and set new buds quickly. If you have a significant drift of plants, shearing them by one-third is an easier option than deadheading. Some varieties will readily re-seed themselves. The plants tend to become leggy and gangly, so pruning will keep the plants looking trim and neat.
Potting and Repotting Sweet Alyssum
Sweet alyssum grows well in containers. When growing in containers, use good quality potting soil and ensure there are drainage holes in the bottom of the pot for excess water to seep out. It’s favored for hanging baskets or window boxes, alone or as a companion to petunias and other similar-care plants. Make sure your container is at least 7 inches wide and deep. If transplanting, fill the container with soil, dig out a hole the size of the existing root ball, put the root ball in the hole, and fill the soil around it. Leave at least two inches between the soil line and the container’s rim.
To overwinter alyssum, cut it down in winter, cover it with frost cloth, or take containers inside. You can also leave it untouched. It’s a prolific self-seeder, so in late winter or early spring, as the ground begins to thaw, you can cut away the dead brush to make way for the seeds left behind from the previous growing season.
Common Pests & Plant Diseases
Sweet alyssum is favored by bees, butterflies, and other pollinators. Since the flowers are accustomed to beneficial insects, it rarely falls victim to common insects. However, bagrada bugs or cyclamen mites are rarer insects, they will infest these plants if given a chance.
To treat the very tiny cyclamen mites, first, try neem oil. If that does not handle the problem, spray insecticidal soap on the plants (usually best in the morning or late afternoon—during less sun intensity). These two treatments are less harmful to beneficial insects.
Bagrada bugs are a type of stink bug invasive in California and Arizona. They are tougher to eradicate and can spread quickly. If you have a significant infestation, pull up the entire plant. The black bugs are also called painted bugs or shield bugs and have orange and white markings. Their shield-shaped body is about 1/4 inch long. Physically remove all the bugs you see, dropping them in warm soapy water. Remove all the egg clusters you see.
This plant is most often affected by fungi like powdery mildew or gray mold (Botrytis blight). These most often occur in cooler, more damp climates. This plant requires well-draining soil and responds to wet feet with clubroot, swollen roots that affect water absorption. Treat this condition by reducing water and applying fungicides regularly.
How to Get Sweet Alyssum to Bloom
Sweet alyssum, as its name suggests, has a sweet aroma, much like honey. Its flowers grow together in close clusters. It takes about two months for a seed to germinate, grow, and bloom. In certain regions, it will bloom all summer. Some frost tolerant varieties bloom in spring and then again in fall. Deadheading the spent flowers will help the plant continue to bloom. Applying a water-soluble fertilizer is the best way to encourage new growth when the blooms appear.
This plant can grow invasively in warmer climates—not needing much of anything to proliferate well on its own in those areas. However, growing outside of those areas can be more difficult. These conditions include the heat index, frost or freezing temps, excessive water, poor drainage, poor soil, or not enough light.
Wilting Flowers and Foliage
If you haven’t planted alyssum in well-drained soil or if it’s very hot, it could wilt. Alyssum does not tolerate intense heat well. Some cultivars have been developed to tolerate hot temperatures without wilting, although the most common types will shrink during the height of summer. You can counterbalance the heat with water, but ensure the soil drains well and efficiently. Bottom line: You should expect wilting. It may rebound in the fall when the temperatures level out some. You can also cut down the wilted plant by one-third, water it, and feed it a water-soluble fertilizer to encourage new growth.
Curling Flowers and Leaves
If you notice curling flowers and foliage, inspect under the leaves and flower petals for mini sap-sucking cyclamen mites. They are hardly visible to the naked eye, appearing like tiny oval spiders if you have a magnifying glass handy. Apply neem oil or insecticidal soap to rid your plant of an infestation.
If you notice your plant’s leaves beginning to yellow, a spike in temperatures can be the cause; either that, transplant shock, lack of water, or poor soil nutrients. Once a plant’s leaves turn yellow, that leaf is dying. One leaf or several yellow leaves is a warning sign and not necessarily a death sentence for the entire plant. Clubroot or another fungal disease can also be the cause. Try to isolate the cause and remedy the growing condition. Once the entire plant wilts, then flowers and foliage are dead. Cut back the plant and wait for more temperate climates or more favorable growing conditions for sweet alyssum to grow back.
Can sweet alyssum grow indoors?
Sweet alyssum can grow indoors. For overwintering, it’s common to bring this plant indoors. Place it in a sunny or partially shady windowsill. It prefers cooler temps; avoid heat sources and draw the shade during the midday sun.
Where should I put sweet alyssum in my home?
Potted sweet alyssum can live near a sunny window with western or eastern sun exposure.
What are alternatives to sweet alyssum?
Since sweet alyssum grows invasively in some warmer climate areas, another similar-looking ground cover that is not invasive in those same areas is a snow-in-summer plant. It also grows in mats like sweet alyssum, bearing tiny white flowers that are deer-resistant and blooms in spring. It is listed as an invasive plant in Alaska. Sweet alyssum and snow-in-winter are suitable substitutes for each other.
Information courtesy of TheSpruce.com