How to Plant and Grow Tweedia

The sky-blue flowers of tweedia are tiny, but they’ll stop you in your tracks. Clear blue flowers are so rarely seen in the garden that these dainty beauties take center stage on many garden tours. Tweedia is native to South America, namely southern Brazil and Uruguay. It is a member of the milkweed or dogbane family (Apocynaceae) and also known as blue milkweed (the only one with blue flowers). It attracts pollinators and makes a striking cut flower. A common cultivar is ‘Heavenly Blue,' which was introduced in the 1980s. 

Tweedia is toxic to humans and pets.

Where to Plant Tweedia

Tweedia needs sun—full sun in northern climates and partial shade in southern climates. Whether you grow it in a container or in the garden, search for a spot that is protected from strong wind. The delicate flowers are easily damaged in heavy gusts and intense rain. A sunny, sheltered corner of a patio or the south or west side of an evergreen shrub often provides excellent shelter for delicate plants. Be sure to place it near the front of a border or near a path where you can admire the daisy-like flowers up close.

The soil should be moist but well-drained. In terms of pH, tweedia is adaptable and can grow in slightly acidic, neutral, and slightly alkaline soil.

How and When to Plant Tweedia

Whether it’s a plant from a nursery or tweedia that you started yourself from seed (more under How to Propagate Tweedia below), wait until after the last spring frost to plant it. Dig a hole at least twice the size of the nursery container and deep enough so that the top of the root ball is level with the soil surface. Backfill the hole and gently tamp down the soil around the base. Water it immediately and keep it moist for the first couple of weeks or so, until the plant is established.

Tweedia is a relatively short vining plant, but it still needs support. At planting time, place a trellis or teepee at its base. You can also insert small branches into the ground alongside the plant for extra support.

Tweedia Care Tips

Light

In climates with cooler summers, tweedia grows best in full sun with at least six hours of sunlight a day but in hot climates, some afternoon shade is preferable.

Soil and Water

As long as the soil is well-drained, tweedia is tolerant of a wide range of soils, including somewhat poor soils. It can grow in a wide pH range between 5.0 and 8.0.

The plant needs consistently moist soil, so water as needed in the absence of rain, about 1 inch per week, more in hot summer weather.

Temperature and Humidity

As a tropical plant, tweedia is not frost-tolerant. It is hardy in Zones 10 and 11 where it can be overwintered outdoors and grown as a perennial. Tweedia thrives in hot weather and has no issues with high humidity.

Fertilizer

Like all annuals that go through vigorous growth in their single-season lifespan, tweedia needs fertilizer. Start feeding it with complete all-purpose fertilizer every two weeks to encourage ongoing bloom. For the amount to use, follow product label directions.

Pruning

To help keep your blue tweedia plant looking full and bushy, pinch the stem tips of the young plants in the spring to encourage branching. 

Potting and Repotting Tweedia

Tweedia can be grown in containers. Make sure they have large drainage holes and fill them with well-draining potting mix. Remember that potted plants need more frequent watering and fertilizer than plants in the landscape. In colder climates, potted plants can be overwintered indoors when placed in a bright and warm location.

When the roots of the plant fill the container, it’s time to repot it.

Pests and Problems

Except for milkweed bugs, tweedia has no major pest or disease issues. Milkweed bugs appear towards the end of the summer, and they don’t do much damage. If there is a real infestation, you can treat it with horticultural soap. Do not use any pesticides, as these will kill the beneficial insects that will flock to your blue milkweed. 

How to Propagate Tweedia

Tweedia is best started from seeds. To get a head start on the growing season, start seeds indoors six to eight weeks before the last predicted frost in your area. Place the seeds on the surface of small pots filled with damp potting mix. Cover the seeds with a very thin layer of soil, only about 1/8 inch. Keep it moist and at a temperature around 70 degrees F. Germination will take 7 to 14 days.

Harden off the seedlings before transplanting them outdoors.

Types of Tweedia

 Tweedia 'Heavenly Blue'

Washed with a hint of turquoise blue and tiny freckles, ‘Heavenly Blue’ develops long, gracefully curving pods that enclose the seeds.

Tweedia 'Heaven Born'

Long-lasting as a cut flower, this twining subshrub usually grows 2-3 feet tall and wide. Leaves are a downy gray-green with an elongated heart shape—they turn red in the fall.

Companion Plants

Fragrant blue flowers combined with velvety-soft gray foliage make tweedia a favorite for a bouquet. Plant a handful of other annuals and perennials that boast great flowers and foliage and you'll be able to create your own bouquets right outside your door. Summer cutting flowers include: 

Purple Coneflower

With its flowers consisting of long, slender petals with a pinkish purple hue, perennial purple coneflower combines beautifully with the blue flowers of tweedia. Zone 3-9

 Sunflower

For cut flowers to be used with tweedia, choose a petite sunflower variety that only grows 2 feet tall. Sunflowers in all colors (orange, red, and yellow) can be combined in a bouquet with tweedia. 

Zinnia

There are so many zinnia varieties that match tweedia, you’ll be spoiled for choice. The soft colors of this annual flower such as dusty rose or mauve are especially attractive in bouquets.