How to Grow and Care for Tweedia

Spruce up your garden with this blue-flowered milkweed

Star shaped blue flowers of tweedia caerulea planted outdoors.
naotoshinkai / Getty Images

Finding a plant with blue flowers is rare, but finding one whose flowers are also fragrant and whose foliage is attractive is even rarer. Tweedia has all three, which has made it a popular choice for gardens, floral arrangements, container gardens, and even bridal bouquets. It pairs nicely in gardens with other late-blooming plants such as lavender, sunflowers, black-eyed Susans, and purple coneflowers (Echinacea). As a part of the milkweed family, it is also beloved by butterflies and other pollinators. Be sure to plant your tweedia in a location where you can admire its beautiful flowers all day long!

Botanical Name Tweedia caerulea
Common Name Tweedia, Blue milkweed, Star of the argentine
Plant Type Perennial, annual
Mature Size 1 to 3 feet tall, 1 foot wide
Sun Exposure Part sun, sun
Soil Type Well-draining soil
Soil pH 5.5 - 7.5
Bloom Time Fall, summer
Flower Color Blue
Hardiness Zones 10-11
Native Area South America
A close up image of blue tweedia caerulea flowers.
chuck b. / Flickr / CC​ BY 2.0

How to Grow Tweedia

Tweedia is a tropical twining vine or subshrub that is native to Brazil and Uruguay. It is a member of the milkweed family and is the only milkweed variety with blue flowers. These flowers are extremely delicate and can be easily damaged by strong winds or intense rain. When choosing a spot in your garden to plant tweedia, ensure you choose a location that is protected from strong winds to ensure your tweedia maintains its gorgeous flowers throughout the whole blooming season.

Tweedia is a relatively easy plant to grow and does not require any special attention. Under the right conditions, tweedia can grow to be up to 3 feet tall and up to 1 foot wide. As a part of the milkweed family, it attracts various types of pollinators and makes a great addition to a butterfly garden.

Light

Tweedia grows best if it is grown in an area with full sun, especially in climates with cooler summers. It will also grow well in partial sun in areas with particularly hot summers.

Soil

Generally, tweedia can tolerate a wide range of soils including poor quality and nutrient-poor soils if necessary. For best results, plant tweedia in moist, well-drained soils. As with most plants, tweedia does not tolerate ‘wet feet,’ or having its roots sitting in water, so ensuring the soil has adequate drainage is important. Adding perlite or sand to the soil will help to increase drainage if needed.

Water

Tweedia requires regular watering in order to thrive. Well-established plants are slightly more drought-tolerant than young plants, but will still do best when watered regularly. If you live in an area that does not receive very much rain, you will need to supplement rainfall with additional watering to help your tweedia thrive.

Temperature and Humidity

Tweedia is a heat-loving plant and requires warm temperatures in order to stay evergreen year-round. In most temperate climates tweedia is grown as an annual, or overwintered indoors as a houseplant and moved outside during the summer.

Fertilizer

Tweedia plants should not be fertilized until they are well-established, at which point they can benefit from fertilization during the growing season to help encourage new growth. Fertilization in the spring and summer months can help to encourage more aggressive blooming in the fall and late summer. A standard all-purpose fertilizer is sufficient for tweedia.

Propagating

Tweedia can be propagated by seeds (see ‘Growing from Seeds’ below) and by taking softwood stem cuttings. To propagate from softwood cuttings, take four- to six-inch stem cuttings from your tweedia plant during the early to late spring. Cuttings should be taken with a sharp knife or pruning shears. Ensure that at least one node is present on the cutting. Remove the leaves and flowers from the lower part of the cutting, leaving at least two leaves at the top of the cutting. Make a fresh cut underneath the node closest to the bottom of the cutting and then dip the cutting in rooting hormone. Place your cuttings in an appropriate rooting medium, water them, and then place them in a location that receives bright (but not direct) sunlight. Roots should begin to grow within four to eight weeks.

Varieties of Tweedia

  • Tweedia caerulea ‘Alba’ is characterized by white flowers.
  • Tweedia caerulea ‘Rosea’ is adorned with beautiful pink flowers.

Toxicity of Tweedia

As with all plants in the milkweed family, tweedia is toxic to humans and pets if ingested. When consumed in large quantities, tweedia can cause cardiac arrest in animals and humans. Generally, homeowners do not have issues with pets ingesting tweedia from their gardens as it has a very strong taste that most animals will avoid.

Pruning

To help keep tweedia looking full and bushy, pinch the stem tips in the spring to encourage branching. In climates where tweedia can be grown outdoors throughout the winter, regular season-end pruning will help to encourage new growth in the spring. Cut back tweedia as you would with other shrubs, being sure not to prune more than a third of the branches off for best results.

Growing from Seeds

Tweedia can be easily grown from seeds, either by purchasing seeds directly or by harvesting seeds and planting them for the next growing season. Depending on the climate that you live in, tweedia seeds can be started in various different ways. When growing tweedia as an annual, seeds can be started indoors in late summer and overwintered until the next growing season. Seeds can also be sowed directly into the garden after the final frost in annual zones. If you are growing tweedia as a perennial, seeds can be sowed directly into the garden, or they can be started indoors and then moved outdoors once they are established. Heated seed mats are recommended for germinating tweedia seeds as they do well when heated from beneath during germination.