Looking at Plants

Acanthus montanus

COMMON NAMES

Alligator Plant, Bear’s Breeches, Mountain Thistle

Acanthus (uh-KAN-thus) – from Greek for “thorn” or “prickle”

montanus (mon-TAY-nus) – pertaining to mountains

GROUP 

Dicot

FAMILY 

Acanthaceae

ORIGIN

Tropical West Africa

DESCRIPTION

Alligator Plant is an herbaceous perennial that averages 4 to 6 feet in height with a 2 to 3 foot spread. It has an open shrubby form with spiny leaves and an aggressive root system. It has a fast growth rate.

Leaves are evergreen, glossy, oblong to lance-shaped, spiny with acuminate tips, deeply lobed, leathery, 10 to 12 inches in length with wavy margins, and dark green in color with silver markings. Some leaves will tend to arch down. The margins of the leaves have sharp spines that curl downward and the leaf ends in a very sharp terminal spine.

The pale pink to white flowers are  borne on 6 to 10 inch long spikes from the branch ends. It blooms summer to fall.

HARDINESS

Hardy in USDA Zones 9 to 11, down to about 20 degrees F. It can be grown as far north as zone 7 with some protection. Hard freezes will damage foliage, but it will usually resprout in the spring if ground temperatures don’t drop much below 15 to 16 degrees F.

LIGHT

Full sun/part shade – though it flowers less in the shade

SALT

Moderate Salt Spray Tolerance – it will tolerate some spray, but it is best to have more protection such as a fence or building as an additional barrier behind the first row of plantings or the first dunes.

SOIL

It will grow on a wide variety of well-drained soils. It doesn’t like overly wet soils.

WATERING

It has moderate drought tolerance once established, so some water is needed for survival in dry spells. As with most plants, though, ample irrigation in droughts keeps it healthier and looking better.

PROPAGATION

Seed; root cuttings taken in early spring

PRUNING

Prune off flower stalk once it is done flowering

FERTILIZING

It has no special fertilizer needs. Unless a soil test suggests otherwise, a slow-release balanced analysis fertilizer applied per the product label will work.

PESTS

Snails - University of California

Slugs - University of Florida

DISEASES

DEER

Resistant

There are very few totally “deer-proof” plants. There are also, relatively speaking, few plants that are considered a preferred food supply of deer. Most plants fall in the big gap between. One of the biggest variables is the available preferred food supply in a given area. If their preferred food is scarce, they will munch on most anything. Given its sharp terminal spines, Alligator Plant would probably not be very high on their list.

OTHER

It has an aggressive creeping root system sometimes making it hard to eradicate.

It is considered an aggressive weed in some areas.

USES

Specimen plant, erosion control, numerous medicinal uses in native land

TOXICITY

A search of ASPCA, Texas A&M University, Canadian Poisonous Plants Information System, University of Wisconsin, Poisonous Houseplants and Ornamentals - Merck Vet Manual, Purdue University - Guide to Toxic Plants in Forages, Poisonous Plants of the Southeastern United States - Alabama Cooperative Extension, Florida Poison Control, and The Cat Fanciers Association did not show this plant on any of their lists.

California Poison Control lists Acanthus spp. as non-toxic.