Cooler temperatures mean planting time in the Rio Grande Valley

Margined Calligrapher Hover Fly on the flower of a Trans-Pecos Spiderwort. (Photo by Anita Westervelt)

Published November 22, 2025, in the McAllen Monitor

Story and photos by Anita Westervelt

The cooler months are ideal for planting in the Rio Grande Valley. As Texas Master Naturalist members, we encourage planting native plants.

Nonnative plants carry the potential to become annoying, get out of control or worse, become invasive and disrupt or destroy the native habitat.

Although it is planting time, it is also a good time to be cautious. There are hundreds of beautiful plants for sale but be careful what you plant.

For instance, a genus of plants in the Commelinaceae family, commonly called the spiderwort family, have about 86 species that are considered native from southern Canada to northern Argentina and including the West Indies.

Four species of the spiderwort family are considered native to Texas, two of which are native to the Rio Grande Valley. Those two are Texas spiderwort, Tradescantia humilis; and prairie spiderwort, Tradescantia occidentalis. The plants in those two species have long, thin, blade-like leaves. Those plants most likely would only be found in the wild.

There are two popular nonnative species of spiderwort that certainly thrive in our special climate: Purple heart, Tradescantia pallida; and trans-Pecos spiderwort, Tradescantia brevifolia. Both species generally have tiny pink flowers with three petals forming a triangular shape about one-half inch in diameter. Their leaves are not blade like, they are short and oval, like an egg, broader in the middle, coming to a point at the tip. Trans-Pecos spiderwort leaves have a blue-green hue; purple heart leaves are darker, many are purple, purple edged or variegated. Flowers of spiderwort, depending on the species, can be white, pink, lavender or blue.

Purple Heart, Tradescantia pallida, Spiderwort plant. (Photo by Anita Westervelt)

Trans-Pecos, Tradescantia brevifolia, Spiderwort plant. (Photo by Anita Westervelt)

This is not a recommendation to add either of these plants to a landscape, but a caution. The plants are very well established in our area because they are not easy to contain nor remove. Their root system is tuberous, thick and fleshy, quickly forming dense clumps that can be quite deep.

Spiderworts spread aggressively through rhizomes and underground stems. Once they are in a landscape in what appears to be an ideal ground cover, they are extremely difficult to remove and to keep weeded of other volunteer plants. Those dense root clumps help the plants store water and nutrients, which give them great survivability. They can thrive in drought conditions.

Spiderworts, easy to spread, not easy to keep free of aggressive, common, volunteer plants, like dayflower, ferns and sorrels. (Photo by Anita Westervelt)

Spiderworts attract pollinators, like bees, wasps and flies. (Photo by Anita Westervelt)

With this month’s cooler temperatures, humidity, and dew-like mornings, the flowers are opening at a great rate. Unless a goal is to rid a garden of these aggressive plants – which is a good idea, but it is not all bad: their nectar and pollen attract bees and wasps and other pollinators, like the margined calligrapher, (see lead photo) a common species of hover fly that is found in many parts of North America, including in the northeast United States.

Margined calligrapher is a good fly. The tiny fly’s size is 0.20 – 0.24 inches. Adult flies feed on a wide range of flowers; its larvae are predators of thrips, aphids and small caterpillars. Interestingly, this species of fly is commonly found in cranberry fields – good news for those of us who love a traditional Thanksgiving meal.

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