Altitude and Wind Affect a Plant’s Water Needs

If you’ve ever gone skiing or hiking in the mountains of the Southwest, you’ve heard the warnings (or ignored them and learned the hard way). Drink lots of water, more water than you normally drink. You also might have noticed that you became breathless a little more quickly. All those warnings aren’t just designed to impress flat-landers or to make up for exertion. There’s science behind high-altitude dehydration of people and plants.

Low Pressure Causes Evaporation

Air pressure is lower at higher altitudes, and that means that moisture evaporates more quickly. It evaporates from lungs and from the soil and roots around plants. Add the fact that most high-desert and mountain climates also are low in humidity, and you’ve got to adapt to a new environment or nearly pass out. The same goes for your landscape, which is another reason to stick with native plants. These guys have toughed it out; they’re not just here for a weekend getaway! If you do choose non-native cultivars, plant them sparingly, and try to use them in protected areas, which leads to my next point.

 

snow on southwestern mountains
My daughter took this photo of snow on the mountains along the Arizona-New Mexico border one December. A holiday snow does not mean a humid climate.

Why Not Add Some Wind to the Mix?

Luckily, winds are worse in New Mexico on the plains than in the mountains. But how about in the high desert? Because of the wide temperature variations – warmer days and cool evenings, desert air can be a little unstable. Anyone driving through rural Arizona and New Mexico is likely to see a few wind farms, a smart renewable energy choice for our state.

Windy air contributes to evaporation. As wind speed increases, plants react by upping their rate of transpiration, which is the plant’s loss of water as it’s absorbed through the roots, up to the leaves, and out the leaves as it evaporates. More than 90 percent of the water a plant absorbs is lost by transpiration. It’s inevitable with photosynthesis.

wind spinner in New Mexico garden
This wind spinner is calm today, but we had to permanently shorten the stake to stabilize it because it almost took off in flight or bent in half a few times this spring.

It’s easy to imagine that wind makes plants drier, as anyone who lives in a windy, arid climate knows when they constantly apply lotion to their skin. Science also explains the effect of wind on evaporation. First, it’s helpful to recognize that plant evaporation increases humidity to an extent. If you’ve ever been in a greenhouse or a tropical plant exhibit, you can feel the humidity as you walk inside.

When the water that travels through a plant reaches a plant’s leaves, it seeps through tiny pores on the underside of the leaves. By hanging out there, the vapor adds to the relative humidity of the air close to the leaf. Kick up the wind, and the leaf moves around, so that it spends time in drier air. Of course, if the air outside is humid that day, the wind won’t have as much effect. But how often is it humid around here? Anyway, high wind, combined with low overall humidity and full sun, can rapidly dry out your vegetables or ornamentals before you know it!

xeric wild rose
No wonder so many xeric plants have smaller leaves. Less transpiration occurs and more energy can go into the plant’s health and blooms. I love this Wood’s rose (Rosa woodsii)., also called a wild rose or Fendler’s rose.

Native Plants Adapt

Native plants adapt to soil and climate. So what about succulents? I won’t get into a long biological discussion, mostly because I am not a biologist or botanist. But one reason that succulents often have small leaves and large stems is to reduce transpiration so they can survive in dry, hot deserts. Others, like the aloes, have a different type of epidermal layer that doesn’t allow for rapid transpiration. It’s amazing how well plants adapt to their environments; if only I could adapt to winter…

Aloe leaves
These aloes have larger leaves, but they lose less water to evaporation than do typical plants.

If you have a non-native that takes slightly more water, remember what I said earlier about protection. Place the higher water user where it’s more protected from wind. If it can take some shade, at least in the hottest afternoon sun of summer, that will help too. Check out past posts for more water-saving tips. And these tips apply to growing vegetables and other edibles in wind and high altitude. The good news for us is that our winds calm slightly by summer.

Favorite Low-water Container Herb: Rosemary

I love rosemary in a container for several reasons. First, I can keep it in a sunny location all year and leave it relatively close to my kitchen to snip stems for cooking. I don’t have to traipse out to the garden to get to it quickly. By leaving the pot close to a south-facing wall in winter, the plant, which is hardy to zones 6 through 8, receives some extra warmth.

rosemary-in-container
Established rosemary in pot that wintered over. I took a few cuttings, but it still has outgrown this narrow container and needs transplanting.

Cutting some rosemary stems for culinary use helps keep the plant compact enough for container living. Otherwise, it might begin to flower and outgrow the pot. When rosemary blooms, it’s an attractive, evergreen Mediterranean plant, and bees love the tiny bluish-lavender flowers. So I usually have at least one rosemary in the landscape, and one or two in containers purely for edible reasons.

Easy-Care Herb

Rosemary is best grown from a nursery transplant or cutting, not from seed. When preparing your container, be sure it has a hole for drainage and mix well-draining soil that’s slightly alkaline and not too fertile. You won’t need to fertilize your rosemary, either, but adding an organic fertilizer when transplanting or once a season shouldn’t harm the plant. Just keep it as warm as you can in winter if you live on the cooler side of the zones, and if you bring the container inside, place it in a sunny location.

rosemary in container
New rosemary plant in a container, ready to head outside for full sun exposure.

Rosemary is drought tolerant and one of the few problems you’ll encounter with rosemary is caused by wet roots when temperatures drop. Rosemary thrives in full sun, and in summer, container plants need some supplemental watering every few days in the heat. Transplant the rosemary to a new container when the plant becomes too large.

Benefits of Rosemary

The aromatic and flavorful leaves of rosemary have many uses. I love the scent of rosemary and lavender in those rice-filled neck warmers! The oil from rosemary leaves is said to help with heartburn and other digestive problems. The oil may also help soothe skin irritated by eczema. Of course, it’s widely used in perfumes, sachets and lotions.

rosemary stems and leaves
The only thing better than looking at a rosemary plant is running your finger over the stems, or cutting some for use in your kitchen!

Culinary Uses

Although rosemary smells great in patio containers and in the home, I love it even more with chicken. You can cut entire stems of fresh rosemary and place them inside a baking chicken or use them in kebobs along with chicken or steak. I love fresh or dried rosemary on potatoes, baked with olive oil, minced garlic and sea salt.

It doesn’t take much rosemary to achieve a lot of flavor, and I haven’t met anyone yet who dislikes the scent or taste of the herb. I often have add rosemary to garlic bread. That’s an easy way to get a little of the flavor of focaccia bread without having to bake!

Use Mulch To Conserve Water In Your Garden

When you put away a gallon of paint or the leftovers from dinner, you always cover the container. By sealing the paint can or plastic storage container, you lock in moisture. It keeps your paint from drying out. Same goes for your spaghetti with pesto (not to mention sealing in the “aroma”…).

Your plant roots can benefit from their own covers, and that’s where mulch enters the picture. Much like the top layer of paint in a can, air dries out the soil at ground level. Add wind and heat, and water can evaporate quickly from desert gardens in particular. Mulch helps insulate the soil to keep it cool and minimize evaporation. The layer of mulch also protects the area around the plant’s roots from the forces of nature. In other words, when the rain comes, it won’t pound the ground, eroding dirt away. Instead, it hits the layer of mulch, then trickles down to the ground. Use an organic mulch and each time it rains or you irrigate, the water carries some nutrients for the roots to take into the plant as well. Need more reasons? Mulching cuts down on weeds, and weeds compete with your plants for water. Plus, they are such a pain.

shredded bark mulch
Mulch cools and moistens barberry, photinia and ice plants in Albuquerque, N.M., bed.

To truly insulate and cool plants takes about three to four inches of mulch material. It depends on the type of material you want to use. If the mulch is fine, such as bark cut to smaller than an inch in size, go only about an inch or two deep. The same goes for grass clippings. Your roots also need some air to thrive! So be sure to avoid use of landscape plastic under your mulch in any areas where you will plant. The plastic is great in walkways, but not in your beds or under trees.

When piling mulch around plant or tree roots, cover the entire area to which the roots extend. For trees, you need to go out about as far as the tree’s canopy. And don’t place the mulch all the way up against the trunk of the tree or stem of the plant. Leave a small opening close to the plant.

mulch around tree
Water is less of a concern in this Northeastern garden/iris farm. But I would worry about how closely the mulch comes to this tree trunk.

Mulches also can look attractive and add to landscape design. Be careful about mulches you choose and social media posts with ideas for repurposing materials as mulches. Some are harmful if applied directly to vegetables and other plants or introduce weeds to your garden. And if your helpful neighbor offers fresh chicken or horse manure, remember that you shouldn’t apply it hot. Add it to your compost, and eventually to the vegetable garden.

gravel around yucca
In the desert of Tucson, the rock around this xeric yucca is probably more for looks, erosion control and night-time heat retention.

We’ll break down some types of mulch in a future post, but if in doubt, check with your local extension office or master gardeners.

Fall List of Water-saving Activities

The weather is cool and plants are going dormant, but there still is plenty homeowners can do to improve water saving and plant health for spring. It will keep you in the water-wise frame of mind and cut down on spring chores.

First, if you have automatic sprinklers or drip systems, be sure to adjust them for your plant’s new winter watering needs. I used to lose it when I would see my neighbors’ lawn sprinklers running full force on a windy and frosty November morning, partly because I nearly froze getting into my car, but mostly because of the wasted water. Watering plants too heavily in fall weather can soften them and make them more vulnerable to frost damage. And if you continue to water them too much in late winter or too soon in early spring so that they leaf out, they’re more vulnerable to late frost damage.

Another good fall project is to mulch around plants. Some xeric plants do better without mulching, but those that need a little more water can benefit from mulches that help retain the moisture. Mulching now also protects more sensitive plants from potential frost.

mulch in bed
Mulch in this bed helps hold in moisture. Note the manual sprinkler control near the home’s front door. It’s not much more work and avoids watering when unnecessary.

Well or shore up plants. Leaving a shallow depression, or tiny well, around low-water plants helps hold moisture in, especially right after they’re planted. If you have some trees and ornamentals that already are established, you can shore up some of the water by building up a ridge of soil around the plant’s base. This is particularly helpful for plants on grades to help prevent water from running off the plant instead of soaking in.

apple_tree_well_web
Tim built up a ridge around this small apple tree to help well the water.

If you’re really feeling industrious, start planning for spring by planning or setting up a water harvesting system. It might be as simple as diverting roof water into a flower bed against the home’s foundation or so that it runs through a dry-river bed (an assortment of rocks and gravel made to look like a river) that leads to a favorite tree. Or plan a new xeric layout for your yard.

calif_poppies
This post lacked color, so I had to add these. Called California or Mexican poppies, they’ll grow in the poorest, driest conditions.