What’s all the hoo-ha about xeriscaping and water-wise gardening? Why does one type of plant make it in our arid climate while another flounders?  Why are some types of plants able to live with seemingly little water while others crisp up and blow away? What is it that makes a plant drought tolerant?

It all starts with physiology. Paraphrasing Merriam-Webster, physiology deals with the functions and activities of living matter. In this case, it would mean the physical structures, activities and organic processes of a plant’s life.

Being that most water is absorbed through the root systems of plants, we'll start there: at the soil level. Averaging only 8 to 14 inches of rain per year, our soils aren't exactly moist. Some plants have the genetic ability to develop a deep root system.  If the soil type will allow, this enables the plant to penetrate soils deeply and extract more water by mining it from a greater volume of soil. A taproot provides food storage, strongly anchors the plant and often begins the development of a deep root system that can draw water from lower soil profiles. If the plant has the genetic makeup to grow deep roots, we can encourage deep root growth through proper irrigation practices.

Moving up from the roots and into the leaves: evapotranspiration (ET) is the loss of water through plant stomata and through evaporation from the soil surface. Stomata are tiny openings on the leaf surface, which are sometimes opened and closed by the plant to regulate water loss. Different plants have different "ET" rates based in part on the size and density of leaf stomata and other leaf features. Plants that can close their stomata, such as green ash, can often endure drought better than those that can not.

Leaf size and shape contribute to drought tolerance as well. Compare the leaves of the fabulously xeric apache plume to those of the east coast wimp, hosta. Apache plume leaves are tiny and rather thick.  Hosta leaves have a larger surface area that loses water more quickly. When supplemental water stops, so goes hosta’s fortitude. Not so the apache plume; arid abuse merely encourages stronger, more erect and robust growth.

One may notice the emerald green of the East and South gives way to a lot of silver, blue-greens and grays here on the Front Range. Physical traits of our drought tolerant plants contribute to this different color palette. These traits help to reflect sunlight, shade the leaf or reduce airflow over the leaf surface. Sage has "trichomes," fine silver hairs that give it a fuzzy texture. Others plants have scales, such as Rocky Mountain juniper. A glaucous sheen, such as seen on the frosted leaves of a sedum, also help to deflect sunlight.

Waxy leaf coverings, or cuticles, also help plants to endure drought. Three-leaf sumac has shiny, waxy green leaves. Pine trees have waxy cuticles. Enduring heat and winds, this waxy coating helps prevent leaf desiccation.

Sedums as well as other succulents like hens and chicks or prickly pear cactus are thick and meaty; drought can be endured through the water-storing leaves. By the end of a long and snowless winter, prickly pear might appear shriveled and deflated. However, it often survives drought partially through the water stored in its succulent structure and with spring snow or rain will plump up to fight another summer.

The more xeric bulbs, such as the tiny crocus and dwarf tulip species, endure drought through water storage in their bulbs. Not only do they endure drought, they also evade drought simply by growing and blooming in the moister spring weeks!

With all the talk about drought, we're besieged with info on drip irrigation systems, alternative turf grasses and water-wise plant lists. It can be overwhelming this flood of foreign information. What happened to Sunday mornings, ambling through the nurseries and mindlessly choosing plants because they look so cute in the pot?

Keep it up! Just focus on the stomatically advanced, tiny-leafed, blue-gray silver-haired fuzzy ones with waxy, shiny,  scaly stuff and fibrous roots shooting out the drain holes in a cloud of glaucousness. Then pray for rain and wish for luck!

For more information see gardening fact sheets and drought.colostate.edu

Q: Will the blizzard that we had in March take us out of the drought?

A:  Probably not. The moisture was very welcome and probably helped a lot in replenishing soil moisture. Our reservoirs, however, are still way below their normal depth for this time of year. Since we have been in a drought for so many years, it will take more than 31” of snow to get us back to average.

Q:  In the current drought situation, should I still aerate my lawn?

A: Yes. Lawn aeration is still a highly recommended spring lawn care practice. While deeper (2-3 inch) core holes provide the greatest benefit to the lawn, even shallow one-inch core holes will help to enhance water infiltration for the spring and summer watering periods.  It will also help to control thatch, an organic layer that often impedes proper water movement into the soil.

Q:  I am planning on putting in some new plants this spring.  What do I need to know about watering them?

A:  All plants, even xeriscape plants, need supplemental water for one to three years to get established.  Group the plants according to their water needs and water them appropriately. Be sure landscape water will be available before planting.

If you had any tree or shrub limb damage from the blizzard and are pruning the limbs yourself, remember NOT to put anything on the wound.  The tree will naturally attempt to close over the wound.  Any kind of wound paint could interfere with this process and create the perfect environment for disease and insects.

Even though the weather can be beautiful this time of year, remember we are only at the beginning of April. Colorado can experience dramatic temperature shifts resulting in freeze damage to new succulent plants.

If you have bulbs that are still covered with snow, push the snow away to allow the underlying bulbs to surface.  Bulbs need warm soil temperatures to shoot up. Colorado often gets heavy wet spring snows.  To protect trees and shrubs from breakage, gently lift up on branches to shake off snow.  Pulling down on branches could easily break already stressed limbs.

The authors have received training through Colorado State University Cooperative Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.

Gardening and Insect Fact Sheets are available on-line by clicking HERE.

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This page updated:  April 3, 2003