Drought Tolerant Plants: Prickly Pears

In the introduction to this series about drought tolerant plants, I defended water efficient gardens by claiming they don’t have to be the “cacti-centric” gardens that many visualize upon hearing terms like “xeriscape,” “water-wise,” and “drought tolerant.” And this is absolutely true. However, that won’t stop me from suggesting that such landscapes include a cactus or two. Despite their menacing and potentially dangerous spines, they are actually quite beautiful, and a cactus in bloom is really a sight to behold. Together with a variety of grasses, herbaceous flowering plants, and shrubs, cactus can add unique forms, textures, and focal points that will enhance the look and function of a water-wise garden. This is why I recommend considering cactus, particularly (as far as this post is concerned) one of the many varieties of prickly pears.

The cactus family (Cactaceae) has a native range that is limited to the Americas. Within that range it is expansive, and cactus species can be found in diverse regions from Canada down to Patagonia. The genus Opuntia (the prickly pears) is the most widespread of any genus in the cactus family consisting of at least 300 species found throughout the Americas. Even a brief investigation into Opuntia will reveal that there is considerable controversy as to how many species there actually are and what to call them. This is partly due to the large ranges that species in this genus can have and the diverse habitats they can be found in within those ranges, resulting in a single species having many forms, varieties, and/or subspecies. Hybridization is also common in this genus where ranges overlap, augmenting the challenge of identification.

Generally, prickly pears have flattened stems with spines and glochids emerging from small bumps called areoles. Their flowers are large, showy and a shade of either yellow, orange, or pink and sometimes white. They form fruits that are either fleshy and juicy with a red or purple hue or hard, dry and a shade of brown or tan. The flattened stems are called pads or cladodes and can be quite large in some species, while diminutive and sometimes rounded in others. Some species are without spines, but all have glochids – tiny, barbed, hair-like structures found in clusters on the stems and fruits. While the spines can be painful when they penetrate skin, the glochids are far more irritating as they easily detach themselves from the plant and work their way into the skin of their victims. The fleshy fruits, called tunas, can be eaten after first taking care to remove the glochid-infested outer layer. The young stems of many species can also be eaten – they are referred to as nopales and are common in Mexican cuisine.

Flowers of Opuntia sp. with bee inside flower on the left

Flowers of Opuntia sp. with bee inside flower on the left

Again speaking generally, prickly pears are very easy to propagate and cultivate. Their two main preferences are full sun and well-drained soil. If you are worried that the soil you are planting them in is going to stay too wet for too long, amend it with some gravel. This is especially important if you live in a climate that receives lots of precipitation or that has cold, wet winters. Once established, prickly pears will move around the garden. If that becomes a problem, expanding plants are easily pruned and traveling plants are easily removed.

I live in a climate that requires the selection of cold hardy prickly pears, so I am taking my specific recommendations from two books: Cacti and Succulents for Cold Climates by Leo J. Chance and Hardy Succulents by Gwen Moore Kelaidis. If you live in a warmer climate, your options will be greater. Still, the options for cold regions are pretty numerous, so for the sake of space I am narrowing my list down to a handful that stand out to me at this particular moment.

Three eastern United States species of prickly pears (O. compressa, O. macrorhiza, and O. humifusa) are, according to Chance, “more capable of dealing with wet and cold conditions than almost any other members of the cactus family.” They still require well-drained soil though. An appealing trait is their large, juicy, red fruits that can add garden interest in late summer and fall. Opuntia engelmannii is another species with the potential to tolerate cold, wet conditions. Its size is appealing to me, with pads that reach a foot wide and plants that grow several feet tall. Chance advises finding “a clone that is known to be cold tolerant” and making some space for it, “as it becomes huge in time.” The most cold tolerant prickly pear may be Opuntia fragilis. It is a diminutive plant with a large native range and a variety of forms, some with rounded pads “shaped like marbles.”

Fruits ("tunas") of Opuntia engelmannii - photo credit: www.eol.org

Fruits (“tunas”) of Opuntia engelmannii – photo credit: www.eol.org

Opuntia fragilis 'Frankfurt' - photo credit: wikimedia commons

Opuntia fragilis ‘Frankfurt’ – photo credit: wikimedia commons

Opuntia polyacantha is a prickly pear native to my home state, Idaho. It is found at high elevations throughout the Intermountain West and is also found on the Great Plains. It has many forms and varieties, and its flowers are various shades of pink or yellow. It is a fast growing species and spreads around easily. Other cold hardy species include Opuntia macrocentra (which has a very attractive yellow flower with a red-orange center), Opuntia erinacea (commonly known as hedgehog prickly pear for its abundant, long spines that can obscure the pads), and Opuntia microdisca (a tiny Argentinian prickly pear with pads that barely reach an inch across but, as Chance says, “works very well in a dry rock garden with other miniatures”).

Pads of Opuntia polyacantha

Pads and spines of Opuntia polyacantha

A post about Opuntia could go on indefinitely due to the sheer number of species and their diverse forms and attributes. This is meant merely to pique your interest. The flowers, if nothing else, should certainly interest you. In her book, Kelaidis calls them “improbably beautiful,” and goes on to say that they are “often papery, always glistening and showy.” Chance likens them to “any fancy rose” because they are “extraordinarily large, brightly colored, [and] eye catching.” Next week, as part of Awkward Botany’s Year of Pollination, I will present another reason to be fascinated with the flowers of Opuntia. For now, I will leave you to ponder this word, “thigmonasty.”

Want to learn more about prickly pears? Check out Opuntia Web.


Drought Tolerant Plants: An Introduction

Water is a precious natural resource and an essential element for life on earth. Demand for water increases dramatically as human population grows and fresh water sources become polluted. Awareness of our reliance on water is especially heightened during times of drought, like the one that California residents are currently experiencing. Some regions of the planet are inherently dry. The region where I live (Boise, Idaho) receives on average about 12 inches of precipitation annually. Compare that to a place like Pensacola, Florida which receives around 65 inches annually, or El Paso, Texas which is lucky to get around 8 inches of rain a year. So whether it is out of necessity (enduring a drought or living in a dry climate) or simply the desire to be a responsible citizen of planet earth, many people are choosing to incorporate more drought tolerant plants in their landscapes in an effort to conserve water.

In the early 1980’s, landscaping with drought tolerant plants was given the name xeriscaping by the Denver, Colorado water department. These days terms like water-wise gardening and water efficient landscaping seem to be more popular. The initial vision that many people may have of a landscape planted with water efficient plants is one filled with desert plants like cacti, yuccas, and other succulents along with drab shrubs like sagebrush. While landscapes like these can actually be quite attractive (see Plantasia Cactus Gardens), modern water-wise gardens do not have to be so cacti-centric. As interest in water efficient plants has grown in recent years, the horticulture industry has been busy introducing a wide variety of plants that are not only drought tolerant but are lush, green, and full of color.

Plantasia Cactus Gardens -Twin Falls, Idaho

Plantasia Cactus Gardens – Twin Falls, Idaho

Plants that live in regions with frequent or extended droughts are called xerophytes. They have developed a variety of mechanisms that allow them to survive and even thrive in these regions. Ecologists call these mechanisms strategies, or sets of coordinated adaptive traits. In future posts I intend to profile specific drought tolerant plants so that we can get to know them on a more individual basis. For now I will provide a brief overview of the strategies plants use to cope with low water environments.

-Alternate Photosynthetic Pathways: Conventional photosynthesis is inherently inefficient when temperatures are high and water availability is low. Plants that evolved in hot and/or dry environments have developed alternate photosynthetic pathways in order to overcome these inefficiencies. These alternate pathways involve utilizing a different protein to fix carbon, splitting the photosynthetic process into two separate cells, and collecting carbon dioxide at night then converting it to sugars during the day. Learn more about the different photosynthetic pathways here.

-Drought Avoidance: Many desert plants live most of their lives as seeds hanging out on the desert floor waiting for rain. These are seeds of short-lived annual plants that sprout and grow when the rainy season comes around. They flower and set seed and are gone by the time the dry season returns. Birdcage evening primrose (Oenothera deltoides) and desert sand verbena (Abronia villosa) are examples of these desert ephemerals.

-Drought Dormancy: Some desert trees and shrubs shed their leaves during dry periods, and then put out new leaves when rains return. This is called drought deciduous. Other desert plants live out the dry season as fleshy roots or underground stems, putting out foliage only when conditions are favorable. Arrowleaf balsamroot (Balsamorhiza sagitatta) is a good example of this; it spends much of the year as a taproot with little or no sign of its existence above ground.

Arrowleaf Balsamroot - Balsamorhiza sagittata

Arrowleaf Balsamroot – Balsamorhiza sagittata

-Physical Adaptations: Desert plants have many physical adaptations that allow them to survive in hot, dry climates. The thick, fleshy leaves of cacti and other succulents store water for future use. The roots of some desert plants are shallow but horizontally extensive in order to capture water more effectively when rains come. The roots of other desert plants extend deep into the ground, some (like the roots of mesquite, Prosopis spp.) even reach as deep as the water table. Palo verdes (Parkinsonia spp.) are drought deciduous trees or shrubs that have photosynthetic bark that can keep photosynthesizing even when leaves are not present. Other adaptations include small leaves, hairy leaves, dull colored leaves, and waxy leaves all of which help to reduce water loss and improve the efficiency of photosynthesis.

Drought tolerant sedums (Sedum spp.) with their shallow roots and succulent leaves are ideal for use on green roofs where temperatures are often high and water is limited.

Drought tolerant sedums (Sedum spp.) with their shallow roots and succulent leaves are ideal for use on green roofs where temperatures are often high and water is limited.

Learn more about how plants cope in low water environments from Arizona-Sonora Desert Museum.