How to Plant, Grow, and Care for ‘Rosie O’Day’ Sweet Alyssum

Need to fill gaps in your garden or add a pop of color to retaining walls? ‘Rosie O'Day’ Sweet Alyssum is a low-growing, beautiful ground cover that boasts shades of pink and magenta. Join organic farmer Jenna Rich as she shares how to plant, grow, and care for this cheerful, pink flowering perennial.

Written by Jenna Rich Last updated: February 15, 2024 | 11 min read

Close-up of a blooming rosie o' day alyssum on a blurred green background. This variety forms low mounds of lush foliage adorned with clusters of tiny, four-petaled flowers. The blossoms feature a soft pink hue, creating a lovely contrast against the plant's dark green leaves.

Contents

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

Close-up of a flowering 'Rosie O'Day' Sweet Alyssum plant in a garden with a blurred background. The plant features dense clusters of tiny, fragrant flowers that bloom in delicate shades of pink. Its narrow, lance-shaped leaves form a lush backdrop to the profusion of blossoms.


Botanical Name Lobularia maritima Plant Type Perennial flowering ground cover often grown as an annual Family Brassicaceae (mustard) Attracts Pollinators, beneficials Special Characteristics Edible flowers, sweet fragrance, drought resistant	Native Area Mediterranean region Exposure Full sun to partial shade Height 4-12 inches Watering Requirements Moderate Alternate Name Alyssum, sweet Alison, carpet flowers	Pests Bagrada bug, caterpillars, aster leafhopper Diseases Root rot and wilt, downy mildew, botrytis blight, leaf blight Maintenance Low Hardiness Zones 5-9, perennial in 9-11 Bloom Time Spring until frost

Rosie O’Day Sweet Alyssum Seeds

Sweetly Scented Mini-Rosettes
Continuous Color
Edible Flowers
All-America Selections Award Winner
Versatile Garden Use

View at Botanicalinterests.com

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

Close-up of rosie o' day plants in bloom against a blurred green background. The blooms are enchanting, showcasing a plethora of dainty flowers adorning the plant in profuse clusters. Each bloom is petite and boasts soft, pastel pink petals that exude a delicate allure. These blooms form dense clusters atop short stems, creating a captivating display of color and fragrance against the backdrop of the plant's lush, lance-shaped foliage. — 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

Close-up of a small bee sitting on a flower in a sunny garden. The flowers are tiny, four-petaled, with small purple-pink petals and yellow stamens, borne in clusters on short stems. — 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

Close-up of 'Rosie O'Day' plants in bloom under sunlight in a garden. The clusters are exquisite, featuring an abundance of tiny, delicate flowers that form dense, rounded clusters atop short stems. Each cluster is composed of numerous small blooms and they are held closely together, creating a profusion of soft pink color. — 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

Macro of blooming inflorescence (Lobularia maritima) with water drops on a blurred garden background. The plant produces an upright small inflorescence of tiny pale pink four-petaled flowers with yellow stamens at the centers. — 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

Close-up of a man's hands holding soil in a garden bed. The soil is loose and dark brown. The gardener's hands are stained with soil. — 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

Close-up of flowering groundcover in a sunny garden. Its foliage consists of small, lance-shaped leaves that form dense mats, providing a lush backdrop for the abundant flowers. The flowers themselves are tiny, and they form dense clusters atop short stems. These blooms are a bright shade of pink. — 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

Close-up of a flower bed with a charming low-growing annual plant that delights with clusters of tiny, fragrant flowers. Its dense mats of delicate, lance-shaped foliage serve as a lovely backdrop for the profusion of small, soft pink blooms that cover the plant. — 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

Close-up of a gardener's hand in a yellow glove pouring liquid fertilizer from a yellow bottle into a blue watering can in a sunny garden. There is a watering can on the ground among the flowering Sweet Alyssum plants. — 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

Close-up of flowering 'Rosie O'Day' Lobularia maritima plants against a blurred background of a sunny garden. This cultivar showcases dense clusters of tiny, fragrant flowers in delicate shades of pink, creating a picturesque carpet effect. The narrow, lance-shaped leaves provide a verdant backdrop to the profusion of blossoms. — 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

Close-up of Lobularia maritima in bloom in a sunny garden. The clusters of flowers present a picturesque sight with their dense and abundant blooms. Each cluster consists of numerous tiny flowers that form a carpet-like effect when in full bloom. These delicate flowers come in various shades including soft pink and hot pink shades, with four petals arranged in a cross shape. — ‘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

View of a flowering 'Rosie O'Day' plant with seeds. The flowers are charmingly delicate, presenting clusters of petite, soft pink blooms atop short stems. These clusters create a picturesque carpet of color against the backdrop of the plant's dense mats of lance-shaped foliage. As the blooms fade, they give way to slender seed pods, which develop in a green hue before maturing to a light brown color. — 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

Close-up of Alissum sprouts in a flower bed with wet soil. The sprouts have thin vertical stems with two green cotyledons, round in shape. — 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

Close-up of a Sweet Alyssum seedling in a small pot on a white background. Sweet Alyssum leaves are small, narrow, and lance-shaped, arranged alternately along the stem. They have a vibrant green color and a slightly fuzzy texture. — 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

Close-up of a flower bed with plants in bloom. The Alyssum plant, characterized by its low-growing and spreading habit, features dense clusters of tiny, fragrant flowers that bloom abundantly in various shades of white and pink, each with four petals forming a cross shape. These delicate blooms adorn the plant's lush foliage, which consists of small, narrow, and lance-shaped leaves arranged alternately along the stems. The flowerbed is fenced with stones. — 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

Top view of seedlings in black pots. The plant produces slender stems and lance-shaped leaves arranged alternately along the stem. The leaves are typically a vibrant green color and have a slightly fuzzy texture. it produces clusters of tiny flowers in white, soft and deep pink. — 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

Close-up of a woman's hand with red nails and a silver-black wristwatch holding an Alyssum seedling against a blurred background of flowering Alyssum plants. The seedling is young and consists of a root ball and several young flowering plants. The flowers are small, star-shaped, consisting of four tiny round petals in shades of white and purple. — 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

Close-up of a flowering plant in a large terracotta hanging pot in a sunny garden. Lobularia maritima, presents a picturesque sight with its dense clusters of tiny, delicately scented flowers in pink hues. The narrow, lance-shaped leaves provide a lush backdrop to the profusion of bloom. — 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

Close-up of a flowering plant Alysson maritime against the backdrop of growing spinach in a sunny garden. This plant features small, lance-shaped leaves that are densely packed along its stems, creating a lush and compact foliage. The plant produces clusters of tiny, fragrant flowers of delicate pink color. — 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

An overhead view of a blooming Rosie O'Day Alyssum among grey-green cineraria foliage. The clusters of Rosie O'Day Alyssum are abundant and compact, boasting a profusion of tiny, fragrant flowers in delicate shades of pink. Cineraria leaves are characterized by their soft, velvety texture and striking silver-gray coloration. The leaves are broad and rounded with scalloped edges. — 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

Close-up of a cluster of pink Alyssum flowers on a blurred green background. A cluster of pink Alyssum flowers presents a charming sight with its numerous small, delicate blooms tightly packed together, forming a profusion of soft pink hues. Each individual flower showcases four petals that create a dainty, star-like shape, complemented by a central cluster of yellow stamens. — 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)

Close-up of many painted bugs on green lanceolate leaves in the garden. Bagrada hilaris, commonly known as the painted bug or harlequin bug, is a small, brightly colored insect characterized by its striking black and orange-red markings on its shield-shaped body. — 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

Close-up of several Diamondback moth larvae on a green leaf in the garden. Diamondback moth larvae, referred to as cabbage worms, are small, pale green caterpillars with a distinctive diamond-shaped pattern along their backs, hence their name. These larvae have a cylindrical body with three pairs of true legs near the head and several pairs of prolegs along the abdomen. Their appearance is characterized by tiny hairs covering their bodies and a slightly tapered rear end. — 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)

Close-up of Macrosteles quadrilineatus, commonly known as the aster leafhopper, on a green leaf. This is a small insect with a slender body typically measuring around 4-5 millimeters in length. It features distinctive greenish-yellow coloring with four prominent dark lines running along its wings, giving it a striped appearance. The aster leafhopper's wings are clear with a delicate network of veins. — 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

View of Alysson maritime with yellowing leaves in the garden. 'Rosie O'Day' a delightful groundcover, boasts dense clusters of tiny, fragrant flowers in delicate shades of pink, creating a picturesque carpet effect. Its narrow, lance-shaped leaves form a dense green mat, providing an attractive backdrop to the profusion of blooms. — 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

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

Close-up of flowering plants whose leaves are affected by gray mold. A charming annual plant, showcases clusters of petite, delicately scented flowers of bright white color. Its small, lance-shaped leaves create a lush green backdrop, accentuating the profusion of blooms that adorn the plant. Some leaves are covered with a grayish-brown coating. — 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

Flower close up. The plant has a cluster of tiny purple-pink flowers with rounded petals. The leaves are narrow, lance-shaped, pale green. — 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.

This might be early signs of downy mildew.

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.