(Blue Milkweed) It's not unusual to see the sky-blue, star-shaped flowers
of Tweedia caerulea tucked into bridal bouquets. Yet they are
members of the humble milkweed family Asclepiadaceae.
Blue Milkweed is a heat-loving species that grows best in a location with full sun and access to a bit of shade. It is native to Uruguay and Southern Brazil and can be planted as a perennial in USDA Cold Hardiness Zones with moderate winter weather. However, it works well as an annual in other zones. You can encourage branching by pinching the flower buds back when growth is young.
Other common names for Blue Milkweed include Southern Star, Star of the Argentine, Silkpods and Star Flower. Another scientific synonym is Oxypetalum coeruleum. Sometimes its petals have lovely purple speckles.
This milkweed is widely grown in New Zealand to provide nectar and host caterpillars for Monarch butterflies.
Caerulea is Latin for blue. In contrast, the genus name honors James Tweedie (1775-1862), the Scottish gardener and plant explorer who found the species in South America during the first half of the 19th century. At the age of 50, Tweedie immigrated to South America and traveled throughout the continent collecting plants to send back to Scotland. He is best known for introducing wild petunias to Europe, which became wildly popular hybrids worldwide.
Here are some guidelines for success with this plant in your garden.
Click on an individual icon for more detailed information.
This plant needs or tolerates more than six hours of intense sunlight daily. Many Salvias only thrive in wide-open locations where they receive long hours of full sun. However, full-sun species sometimes tolerate a bit of partial shade. Or a Salvia that loves partial shade may be amenable to spending part of its time in full sun.
In general, this sun/shade adaptability shows up in Salvias that do best in cooler climates when grown in full sun and thrive in hot climates when partial shade is available. So full-sun Salvias sometimes are also categorized as partial-shade plants and vice versa.
This plant can handle extreme heat.
Full-sun Salvias that don’t like any shade are among the most heat tolerant. Heat-loving Salvias also are often drought tolerant. Moisture-conserving features, such as fuzzy leaves, help them stay perky at high temperatures.
Heat-tolerant Salvias are fine choices for western and southern exposures.
This plant grows well in an outdoor container, such as on a patio.
Some containerized Salvias leaf out and flower year after year following a period of dormancy. Annuals in containers may die back and appear to grow again when they reseed.
During extreme heat, check the soil in container plantings once or twice daily to be sure it doesn't completely dry out. Feel its surface for coolness, then gently poke a finger into the soil to check for dryness.
Plant hardiness Zones defined by the U.S. Department of Agriculture tell you the minimum temperatures a plant can withstand in your garden. The USDA divides the nation into winter climate areas from coldest (Zone 1) to warmest (Zone 11).
However, it is sometimes possible to grow a Zone 6 Salvia as a perennial in Zone 5 if you provide preferential care, such as winter mulching and a location sheltered from harsh winds. In contrast, a Zone 9 Salvia may act like a perennial in Zone 10 if given a bit of shade or extra water.
To create a harmonious landscape plan, it is important to consider the heights of individual plants.
Height also affects function. Short Salvias often make excellent ground covers that conserve soil moisture and discourage weeds while also brightening your yard. Medium-height Salvias, such as ones 36 inches tall, often are ideal border plants. A tall Salvia planted singly can highlight a landscape; multiple plantings can form an attractive screen.
By considering the width of a plant, you can determine how many to place in a row or what other plants to grow with it.
For example, a narrow, moderate-height Salvia may look good interplanted with bushier species, kind of like Mutt and Jeff.
In contrast, wide-spreading Salvias are economical for hiding lengths of wall and fence or for creating hedge-like divisions in a yard.
Plant this herbaceous species in the USDA Zones where it grows as a perennial, returning year after year.
After dying back to the ground at frost, herbaceous perennials emerge in the Spring with soft, new growth. A Salvia that is perennial in one region, may be an annual in another depending on local conditions, such as winter temperatures.
If you live in USDA Zone 5, for example, Salvias in our catalog cited as growing well in Zone 5 or lower will be perennial. Those cited as doing well in Zones 6 or higher may do well in Zone 5, but generally will act like annuals coming back from seed instead of the parent plant’s roots.
This plant needs regular watering based on what is appropriate to your local conditions.
In some extremely hot, arid climates, this may mean daily watering in Summer. Although many drought-resistant Salvias survive on little to no watering due to local rainfall and deep roots meeting their moisture needs, others need regular doses. The size and frequency of the dose depends on your climate.
In the right locale, this plant survives and thrives despite minimal summer water.
Drought resistance is an important characteristic of xeriscapic – dry landscape – plants, a category that includes a multitude of Salvias. Many low-water Salvias are native to parts of the world with little rainfall all year or regions where summers are dry and winters are wet.
Nevertheless, there are also drought-resistant Salvias for places such as Florida where winters are dry and summers are wet.
This plant reaches peak bloom in Fall or flowers for much of the season.
It may begin flowering much earlier in the year. Bloom time for some Salvias lasts from Spring till first frost. Others begin flowering in Summer and continue into Fall. There are also Salvias that don’t bloom until late Fall and continue into Winter if grown in mild-Winter areas.
There is a great deal of overlap in blooming seasons for Salvias.
This plant reaches peak bloom during Spring or flowers for much of the season.
However, it may begin flowering sooner. Some Spring-blooming Salvias begin flowering in Winter; others start in Spring, keep producing color through summer and may continue on into autumn and first frost. Still others flower only in Spring.
There is a great deal of overlap in blooming seasons for Salvias.
This plant attracts butterflies whether for nectar or as a host for their caterpillars. Some butterflies feed on a limited range of flowering plants and only lay eggs on one kind of host plant. Salvia nectar lures adult butterflies. Placing host plants, such as Milkweeds (Asclepias spp.), next to nectar plants builds butterfly habitat. In exchange, the butterflies improve fertility in your garden through pollination.
Unless local forage is in short supply, most deer likely will avoid this plant.
It appears that deer dislike Salvias, in general, due to their volatile oils that make the plants so fragrant and savory in cooking. However, the only completely deer-proof plants are the ones grown beyond reach.
(Caucasus Sage) This hardy ground cover sage grows 4 to 12 inches tall and 12 inches wide. The velvety white fur of its foliage aids moisture retention. Its soft, royal purple flowers make it stand out. We think this Salvia deserves to spread far and wide.
(Ember's Wish Sage) Bright coral-colored, tubular blossoms contrast handsomely with the deep maroon stems, rusty rose calyxes and mid-green foliage of Ember's Wish Sage.
(Scarlet Spires Sage) This is a brilliant cross between the sturdy D'Arcy's Sage (Salvia darcyi) and the beautifully colored 'Raspberry Delight' Littleleaf Sage (Salvia microphylla 'Raspberry Delight').
(Scorching Pink Mountain Sage) Compact and small, this Mountain Sage is another fine groundcover for Southern California, the Southwest and Texas. Similar to Salvia microphylla 'Heatwave Glimmer', it not only survives but thrives in extreme heat.
(Magic Wand Sage) Salvia x ‘Magic Wand’ is perky with vertical spikes of long blooming, rich purple flowers and dense, mid-green foliage. Overall, it reminds us of Salvia x ‘Big Blue’, but has smaller flowers and usually doesn’t grow as tall.