Nurse Rocks

(Photograph = Echinocactus polycephalus var. xeranthemoides, Nancy Hussey)

Introduction

Sometimes desert seedlings start life under a shrub. The shrub provides protection from too-hot sun, drying wind, and even cold temperatures. These shrubs are nurse plants. But what about nurse rocks?

The Details

Some cacti grow in sandy soils—Opuntia polyacantha var. erinacea near Kingman, Arizona, for example—but many xeric (very dry-habitat) cacti and succulents are found mainly in rocky soils.

Moisture is held under rocks—the last rains might have been weeks ago, but a large surface rock can still trap a bit of moisture beneath it. Shallow, laterally spreading roots can collect that water. In fact, most cacti have shallow root systems—tailor-made for exploiting moisture under surface rocks.

The crevices between rocks also provide protected zones for tiny seedlings. They may germinate in small gaps where drying wind is reduced, shade is available during the hottest hours, and daytime heat stored by rocks can buffer freezing nights.

Even in harsh deserts, there are microclimates—spots slightly cooler than full sun and with other advantages. These tiny oases matter for tender seedlings. A mature cactus can take all the desert can throw at it, but seedlings need help. Nurse rocks can provide that help.

Additional Reading: Nurse Plants

Agave utahensis (nevadensis?), Nancy Hussey

ferocactus cylindraceus, Nancy Hussey

Echinocactus polycephalus xeranthemoides with rose, Nancy Hussey

Ferocactus, Echinocactus, and two yucca species, Nancy Hussey

Ferocactus cylindraceus with Fouqueria splendens, Nancy Hussey

Echinocereus engelmannii, Nancy Hussy

^{(Photograph = Echnocactus polycephalus xeranthemoides)}