Witchgrass (Panicum capillare L.)

↑Habitat

Witchgrass prefers average to dry disturbed sites in full sun, in relatively barren soil. A range of soil types are tolerated, including sand, gravel, rock, or hardpan. Natural habitats include disturbed sites in prairies, sand dunes, rocky barrens or outcroppings on limestone, sandstone, chert, or granite, and gravel bars along rivers. Witchgrass is also common in anthropogenic habitats including railroad along gravel (especially in limestone gravel), cropland, construction sites, cracks in cement or asphault along roads and in cities, and industrial areas.

It is largely indifferent to pH, tolerating both acidic and alkaline soil, and often more likely on the extremes as there is less competition from other plants. Although it is capable of growing on moister sites and in more fertile soils, it rarely reaches maturity on such soils because it gets out-competed by other plants.

↑Life Cycle

This species is a native warm-season annual grass.

Seeds germinate when on or near the surface of exposed soil at the start of the warm season, after a period of cold dormancy. Seeds that are not in suitably sunny conditions during this time may not germinate. Germination time is fairly flexible, ranging from spring into summer, and is triggered by a combination of temperatures above 20°C (about 68°F) and light. Seeds do not need light to germinate, but relatively few will germinate in darker conditions. Moisture does not appreciably affect germination.

Seeds that do not germinate may persist in the seed bank for up to 3-4 years, possibly longer, but viability decreases, particularly after the first year. Seeds buried deeper seem to retain viability longer, and typically germinate if the soil is disturbed so as to bring the seed up from the lower layers.

Seedlings tend to be drought-tolerant from the onset, but are highly sensitive to competition. As such they often establish better under conditions of drought stress. Established plants have some ability to push up through other plants to compete. Plants without competition and on drier sites typically develop a sprawling growth habit, low to the ground, often with a rosette pattern where many stems originate from the same point but each is unbranched. Plants with more competition, on richer sites will typically grow upright to reach more sunlight and may rely on competing vegetation for support.

When mature, the entire inflorescence breaks off and becomes a tumbleweed, helping distribute this grass to new locations; the grains are more loosely-attached to the inflorescence stalks, thus causing them to be shed gradually as the inflorescence blows around in the wind.

The size of plants at maturity is highly variable based on nutrient and moisture availability, typically ranging from under 1 foot to about 3 feet high.

↑Links & External Resources

• Panicum capillare (witchgrass) | USDA PLANTS Database (About This Site)

• Panicum capillare | Go Botany (About This Site)

• Panicum capillare | Biota of North America Project (BONAP) (About This Site)

• Panicum capillare | NatureServe Explorer (About This Site)

• Panicum capillare | Flora of North America (About This Site)

• Panicum capillare capillare (Witch Grass)† | Illinois Wildflowers (About This Site)

• Witchgrass | Maryland Biodiversity Project (About This Site)

• Panicum capillare L. ssp. capillare (Witch Grass) | Digital Atlas of the Virginia Flora (About This Site)