Sweet alyssum is a dainty, low-growing ground cover. ‘Rosie O’Day’ is a mixed pink version of the classic white everyone knows and loves. In this article, I’ll discuss how to plant, grow, and care for it.
Let’s get started.
Overview
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Rosie O’Day Sweet Alyssum Seeds
What Is It?
Sweet alyssum is a short-lived perennial in zones 9-11 or an annual in zones 5-9. It’s a low-growing ground cover in the mustard family native to the Mediterranean regions that range in colors from white to shades of pink and purple.
Their tiny, dainty flowers are non-toxic and used as garnish on platters, soups, and desserts. ‘Rosie O’Day’ alyssum was an All-America Selections award winner in 1961. It’s a rosy pink version of everyone’s favorite companion plant.
Appearance
These plants form a lush carpet of pink-magenta flowers.
‘Rosie O’Day’ grows up to 12 inches in height with a 6-12 inch spread. It features tiny, four-petaled flowers ranging from soft pink to magenta with soft yellow centers, rightfully nicknamed carpet flower as it forms a carpet of lush florets. The leaves are medium green, long, oval, and narrow.
This flower grows well along retaining walls, in rock gardens, or in fairy gardens. ‘Rosie O’Day’ will spill over walls and rocks, fill in cracks and crevices, and be abuzz with pollinators, filling the air with a sweet fragrance.
Standout Feature
Attract diverse pollinators and beneficial insects like hoverflies and ladybugs with this pink ground cover.
Pollinators of all shapes and sizes are drawn to this plant, like hummingbirds, butterflies, bumblebees, and honeybees. However, little guys like hoverflies adore the tiny flowers because it’s easy for them to reach the sweet nectar.
‘Rosie’ serves as an insectary plant and attracts beneficial predators to the area, which will feed on pests like aphids.
How to Grow
Alyssum is low-maintenance and can adapt well to different types of soil and climates. It matures in 60-90 days from sowing. Let’s discuss how to care for this easy-growing plant.
Sunlight Requirements
Alyssum thrives in full sun to partial shade, growing throughout the season.
If you have a spot in your garden that receives full sun to partial shade, alyssum will thrive. Though it may peter out in the peak of summer, it will grow all season long with the right conditions. In warmer zones, some afternoon shade will benefit the plant. At least six hours of direct sun is needed in cooler zones.
Water Requirements
Drought-resistant ‘Rosie O’Day’ needs one inch of water per week.
While ‘Rosie O’Day’ is drought-resistant once established, it should receive one inch of irrigation per week if no rainfall has occurred. Perform the finger test by sticking two fingers into the soil as far down as you can. They should come out with about two inches of moist soil on them, and if not, it’s time to water.
Soil Requirements
Use well-draining soil, add garden grit if necessary, and maintain pH between 6.0-7.0.
Soil can be rich, sandy, or loamy, but it must be well-draining, or root rot can occur. Add a little garden grit to help with drainage if needed. Test the soil and amend it to get the pH between 6.0 and 7.0. Keep the soil moist throughout the season. It might not look like much during the summer, but blooms should return in the fall.
Alyssum won’t need amendments in its soil unless the soil is compacted and doesn’t drain well. Too much fertility is not good for the overall performance of this plant.
Mulch
Mulching ‘Rosie O’Day’ alyssum is optional but can suppress weeds and cool soil.
Providing mulch for ‘Rosie O’Day’ is not necessary unless it’s part of your garden design. Alyssum can serve as a mulch under other taller shrubs, trees, and perennial flowers once they start to cover the ground, suppressing weeds and keeping the soil cool.
Climate and Temperature Requirements
The blooms appear mainly in spring and fall.
Most flowering occurs in the cooler temperatures of spring and fall. The plant can withstand temperatures down to 28°F (-2°C). If a frost is in the forecast, add a layer of row cover to keep the plants protected. Preferred temperatures are between 50 and 60°F (10-16°C). ‘Rosie O’Day’ may peter out a bit in the peak of summer.
‘Rosie O’Day’, like most alyssum cultivars, is mostly grown as an annual in cooler regions. It’s easy to start from seed and may be best as an annual. That’s because it can get leggy in its second year when grown as a perennial. However, it can be grown as a winter-blooming perennial in zones 9-11.
Fertilizing
Apply phosphorus-rich, nitrogen-low organic liquid fertilizer every 3 weeks in spring and fall.
Alyssum responds best to fertilizer in the spring and fall to coincide with its peak bloom periods. Add an organic liquid fertilizer diluted to 1/4 strength one or two times in the season, stopping once temperatures go above 50°F (10°C) when it stops uptaking nutrients.
Choose one that’s high in phosphorus and low in nitrogen. Apply after irrigating or rainfall. Always refer to the instructions on the packaging of the fertilizer you are using.
Harvesting
Pick ‘Rosie O’Day’ by snipping full stems, creating a romantic backyard bouquet.
Harvest full stems of ’Rosie O’Day’ by snipping them near the base with clean, sharp shears. Add it to a mason jar with some sprigs of ornamental grass and a few bright, disc-shaped flowers for a romantic backyard bouquet.
‘Rosie O’Day’ will add an earthy, mustardy flavor when used as an edible garnish. Harvest healthy-looking flower clusters when they’re in full bloom. You can also snip off whole stems, depending on how many you need.
Pruning
‘Rosie O’Day’ doesn’t need it but appreciates light pruning for new growth.
This plant does not require any pruning. However, if you notice lots of brown petals and want to freshen it up, a light prune will be appreciated and would encourage new growth. Any dead and diseased areas of plant should be pruned as you notice them.
Collecting Seeds
Collect mature seeds from lower clusters and store them in a dry place.
Scout for seeds on lower, more mature flower clusters as seed pods will form there first. They’ll be brown and dry, like small, slightly flatter coriander seeds. Gently tug the stem off the plant or snip it off. Roll the stems gently between your fingers to release the seeds from the pod. Do this over a colander, paper towel, or bowl to easily separate the seeds from the rest of the stems.
If it’s late in the season and the plant has started to die back, lift the plant stems, sweep the seeds out from the soil surface, and separate them from plant debris. Ensure seeds are 100% dried before adding them to a cloth bag, brown bag, or plastic container, and store them in a cool, dry place in your home. Label them with the variety and year.
Propagation
While dividing is not recommended, you can grow this plant by seed, cuttings, or allow the plants to self-seed. Having more alyssum to plant in your garden is always a plus!
Starting From Seed
Grow ‘Rosie O’Day’ seeds indoors before the last frost and provide light for germination.
Sow seeds indoors four to five weeks before the last frost and place them under lights or on a windowsill. Light is required for germination, which may take 5-15 days.
Bottom water your cell trays or containers to keep the seeds in place and keep the soil moist. Direct sow by sprinkling 15-20 seeds every foot. Thin as needed, but it’s really not necessary. The plant enjoys growing in masses of living mulch.
Pro tip: In mild climates, seeds can be sown in the fall for winter blooming.
From Cuttings
Snip stem cuttings, plant in fresh soil, keep moist, and transplant when rooted.
Create new plants from cuttings by snipping the top four inches from a few stems and placing them into fresh soil. Keep them well-watered and protected as they form new roots. When you tug the stem gently and there is resistance, roots have formed.
Transplant them outdoors when roots are ample and healthy, or place them in a container to allow them to continue growing. Cuttings are recommended for warmer regions where this plant grows as a perennial.
Self-Seeding
Remove unwanted self-seeded seedlings to prevent white flower reversion.
This is a prolific self-seeder, but most hybrids will revert to white flowers the following season. Pull up any unwanted shallow-rooted sweet alyssum seedlings that germinate. You should be diligent about this if you want to plant something else in that spot next season.
Planting
Alyssum isn’t fussy when transplanted and can be done in the spring or fall. Remember to harden off your seedlings and be gentle in the transplanting process. These plants don’t have extra sensitive roots, though.
Hardening Off
Ensure seedlings are hardened off at 50°F (10°C) and protect from late frosts to prevent damage.
Harden off seedlings at around 50°F (10°C) before transplanting so they can acclimate to outdoor conditions. Protect seedlings in the event of any late spring frost. They can handle temperatures down to 28°F (-2°C), but young seedlings are especially vulnerable to death by frost.
Spacing
Ideally, spacing of transplants should be six to eight inches. If you are using sweet alyssum to canopy the soil surface of annual vegetables such as tomatoes, more space will be appreciated for good airflow. Less is fine in gardens where you want to cover the soil quickly, but you’ll find upkeep requires more effort.
Transplanting
Transplant ‘Rosie O’Day’ after frost risk, relocate established plants to sunny, well-draining spots.
After properly hardening off, transplant ‘Rosie O’Day’ after the risk of frost has passed. Avoid doing so in the heat of summer as the roots won’t have time to adjust to the warm soil temperatures, and require extra water to establish.
You can move established plants to a new place in your garden or gift to a friend or neighbor. Ensure soil is well-draining and it receives Full sun. Fertilizer can be added at this time. Water well until it’s established.
Pro tip: Don’t let the soil get soggy when planting alyssum in containers.
Plant Uses
The delicate pink flowers of ‘Rosie O’Day’ will complement many flowers, plants, and trees you have growing in your garden. It does great in containers and on sloped land.
Design Ideas
Grow ‘Rosie O’Day’ in window boxes, containers, or on slopes for a fragrant, pollinator-friendly garden.
‘Rosie O’Day’ will create rolling folds of lovely pink flowers over retaining walls. This plant looks great in window boxes, and you’ll love smelling its fragrance when it’s placed in a container near your front door.
Try it as an understory in your cottage garden. Sprinkle seeds between large patio stepping stones, or add it to a pollinator garden. Got sloped land? Throw some seeds there instead of grass for a pollinator-friendly area. Grow it with various herbs such as lavender, rosemary, and Russian sage, or along a walkway or garden border.
Insectary Plant
Plant alyssum near vegetables to attract beneficial insects for pest control.
Place alyssum near vegetable crops, and you’ll notice them buzzing with parasitic wasps, hoverflies, and minute pirate bugs, all of which are extremely prolific predators of multiple damaging garden pests.
Studies show when sweet alyssum is intercropped with certain vegetables, the populations and overall health of some beneficials increase. This leads to better control of garden pests like aphids, spider mites, moths, mealy bugs, and various pest eggs.
Companion Plants
Boost pollination for peppers, eggplant, and tomatoes while deterring weeds and pests.
Sweet alyssum may increase the rate of pollination of annuals like peppers, eggplant, and tomatoes. Additionally, it will suppress weeds and attract pollinators and beneficials, which may lead to decreased pest pressure.
Edible Flowers
Use the flowers as a salad garnish, or in cakes, pasta, or cocktails.
This pretty flower is edible! Add the mustardy flowers as a garnish in salads or stews. They also add a delicate feature to a white cake, atop a summer pasta dish, or floating in a cocktail.
Common Problems
Here are a few pests and diseases to be aware of, although they aren’t huge threats to sweet alyssum. While these pests are typically a threat on young plants, and in large numbers, mature plants have little issue with them.
Pests
Painted bug or Bagrada bug (Bagrada hilaris)
The Bagrada bug, a smaller stink bug, harms mustardy crops, causing spotting and wilting.
This bug is a type of stink bug that loves mustardy crops. It looks like a tiny Harlequin bug with similar black, white, and orange markings, and a shield-shaped body, but about half the size. Nymphs resemble lady beetles nymphs, which hatch out in the spring and fall. This pest thrives in the heat of summer, hiding in the soil during cooler parts of the day.
Bagrada bugs pierce plant tissues to feed on the insides. Symptoms include spotting, stunted growth, wilting, or death. Scout early for early detection, keep your soil healthy, and use trap cropping to prevent an infestation. Infested plants should be promptly removed and the area kept weed-free.
Caterpillars
Scout early for diamondback moth larvae and cabbage loopers.
Any caterpillar can be damaging in the garden, but diamondback moth larvae and cabbage loopers are two that can cause some serious damage. They chew circular holes in leaves, giving them a shothole effect, and chew through the leaf tissue, respectively.
Scout early and toss any found into a jar of soapy water. Crop rotation, insect netting during the proper life cycles of various caterpillars, and a tidy garden should decrease the risk.
Aster leafhopper (Macrosteles quadrilineatus)
Watch out for tiny grayish-green hoppers that spread aster yellows, causing a mottled plant appearance.
These pesky hoppers can transmit Aster Yellows to healthy plants, and unfortunately, they’re hard to spot at ⅛ inch in size and grayish-green. Their preferred host plants range widely, so there are lots of things you have in the garden they’ll likely love to feed on. They cause a mottled appearance after sucking out the juices of plants.
Two to three generations of nymphs may hatch out per season, occurring in June and July. Remove possible weed hosts and look for symptoms of aster yellows in surrounding plants.
‘Rosie O’Day’ is safe from deer and rabbit damage.
Diseases
Root rot and wilt
Rhizoctonia solani causes root rot, leading to yellowing, wilting, and collapse.
Root rot is caused by Rhizoctonia solani, which proliferates when the root below the surface can’t breathe. This is due to compacted soil, too much water, or too dense of a planting. Above-ground symptoms include yellowing, wilting, and foliar collapse.
If you have heavier soil, minimize water and use a soil moisture meter to avoid overwatering. Plants will not likely survive root rot and should be removed.
Downy mildew
Yellowing leaves indicate DM by Peronospora, leading to fuzzy spots and potential plant death.
Upper leaf yellowing may indicate downy mildew, caused by Peronospora. Fuzzy mildew spots will form as the infection breaks through the leaves. Leaves will shrivel up, and if the infection persists, plants may die.
Keep plants healthy and water in the early morning to avoid wet foliage going into the night. This decreases the risk of fungal activity and fungal disease. Give plants ample space and provide good airflow.
Botrytis blight or gray mold
Botrytis cinerea causes gray mold in wet areas.
Gray mold is a risk when alyssum is grown in wet areas and is caused by Botrytis cinerea. When browning begins on the inner edge versus the outer edge of the flower, the plant is likely experiencing gray mold. You may also see large areas of fuzzy, gray spores, and some leaves may drop and die.
Practice good sanitation in your garden, including changing gloves and cleaning tools. Also, clean up garden debris, including fallen leaves and any infected plants.
Leaf blight
Prevent blight with quality seeds, humidity control, drip irrigation, and sanitation.
Generally caused by wet conditions and humidity, blight causes yellowing in all areas of a plant and can eventually cause death. Source your seeds from reputable sources, control humidity levels, use drip irrigation, and practice good sanitation in your garden to prevent it. Copper-based fungicides may be used as preventatives before extended periods of rain and humidity.
Frequently Asked Questions
Yellowing is likely caused by pests like mealybugs, aphids, and leafhoppers. Pay close attention though as yellowing is often a sign of something serious like downy mildew or root rot.
Final Thoughts
‘Rosie O’Day’ is a charming pink groundcover that can be grown as an annual or perennial, depending on your region. It’s versatile in its uses and is adaptable to different climates and soil types. Look no further for low-maintenance and beneficial ground cover.
