A Microclimate Experiment

Microclimates can be a farmer’s or gardener’s best friend. A few years ago, I wrote about how use of microclimates, or pockets of a garden that have varying temperatures and exposures to weather elements, can expand your choice of xeric plants.

cactus greenhouse atlanta
This greenhouse in an Atlanta-area garden provides extra heat and sun for the homeowner’s succulent collection and keeps rain off the plants!

The easiest example of a microclimate is a greenhouse. Windows let sun in and walls, a roof and other strategies help maintain the warmth. Add a heating source (and enough space) and you can grow nearly any plant any time of year.

lava rocks microclimate
The Desert Garden at the Huntington in San Marino, California, is a perfect microclimate for cacti. Not so perfect for humans on the day we visited. The lava rocks intensified the 100-plus temperatures.

Subtle microclimates exist all around your yard and gardens. Structures and hardscaping absorb heat during warm hours and release it gradually, helping to protect plants from cold; they also can protect plants from wind. Partial shade shields plants from heat, and slopes or other topography alter how the overall climate affects a given plant.

pond water lilies
Not far from the Huntington, a homeowner’s pond was filled with blooming water lilies in basically the same climate.

The Zinnia Experiment

I would like to say that we planted zinnia seeds in three different places simply to later show how microclimates affected their growth and hardiness. But I’d be pushing the truth. I did plant them in several different spots to see how well they grow here and how quickly they bloom, so I can use them as an easy annual filler to add color and even more pollinators to our gardens.

So, we put seeds in open space in our vegetable farm rows, mostly for the pollinators. We also planted some on a fairly exposed raised bed in our xeric garden. Finally, we planted seeds in the lower part of the xeric garden, close to the rock wall. All of the flowers did fairly well, although the ones in the farm area had better soil and more consistent drip watering. They were the tallest and healthiest. The ones in the raised bed took longer to come up, likely because of poorer soil and an inconvenient hand-watering location. The flowers planted in the lower bed did almost as well as the ones in the farm area.

zinnia cold damage
The healthiest zinnias froze the most, likely because of the farm area location and the fact we had pulled up several rows of faded vegetable plants, so these zinnias were open to a pocket of frost.

Then the frost came and the healthiest plants burned the worst. They more or less bit it overnight.

The zinnias in the raised bed were nearly as bad, but at least the flowers kept their color (I planned to take photos of them, but hard-working hubby cleaned up the bed before I had a chance.)

zinnias minor frost damage
These zinnias suffered some frost damage, but the flowers were still vibrant, thanks to their protected location near the rock wall.

The zinnias in the lower bed fared the best. I doubt they will grow or flower more, but they don’t look like they belong in a horror movie.

How to Use Microclimates

The experiment helped me get a sense of microclimates on our land. We’ve always assumed that our farming area is cooler because it is in a sort of mini-valley jut above the river. The dead zinnias demonstrated we were right, especially since those plants were the most robust before the freeze hit. The flowers in the raised bed are more open to cool air; there were no other plants nearby or much hardscape to absorb heat either.

The hardiness of the zinnias in a more protected and “solarized” spot near the rocks was telling. It’s always important to think about sun and shade exposure, but sometimes we fail to consider how placing a few large rocks behind a cold-sensitive plant can help it survive winter. In vegetable gardening, for example, using fabric to cover plants creates a micro-greenhouse effect. And when growing a plant that needs a little less sun or heat, shade cloth or plant placement can lengthen growing seasons.

shade for vegetable plants
Peppers love heat, but these pepper plants in Tucson had shade over them for protection.

Microclimates, like the general climate, can vary. For example, a tree that drops its leaves provides no shade until it fills in late spring. As trees mature, they can begin shading a plant that once received full sun; it might be time to transplant a shaded shrub. Windbreaks help slow the flow of cold air streaming up a slope.

rio Ruidoso bench
Every gardener needs a microclimate too! we placed this bench in a shaded area near the river as a spot to cool off on warm days working outside.

Containers offer excellent microclimates, not only because they warm up quickly, but because you can move them to solve sun and wind exposure issues, and all the way inside before the first frost.

adenium in container
This Desert Rose (Adenium) in Tucson is about 10 times the size of ours. But its location in a container means that botanical garden staff can move it if necessary for changing seasons and microclimates.

Five Favorite Cold-Hardy, Low-Water Perennials

With winter in full swing, I’m amazed at the hardiness of some of our low-water plants. Anyone who lives in a northern or high-altitude zone who’s planning to add or replace some plants this spring with low-water alternatives should feel plenty comfortable with the number and variety of choices. Planting perennials saves you money – and water. Xeric perennials only need a boost of water the first year or so, and then can often make it with no irrigation. Here are a few of my favorites by category:

purple iceplant low water cold hardy perennial
This purple iceplant had a few blooms into fall; we’ve had them covered with blooms in summer.

Ground Cover

The iceplant (Delosperma) is a sun-loving groundcover that spreads rapidly and rewards gardeners with bright pinkish-purple (D. cooperi) or yellow (D. congestum or D. nubigenum) flowers. We thought it would be too cold here in zone 6B, but our purple iceplant thrives on the northeast side of our home. It’s a stunner, especially in rock gardens, where it can cascade slightly over rocks or borders. It’s also an easy groundcover to transplant. Other low-water cold-hardy groundcovers are several sedums, such as Dragon’s blood (Sedum spurium), and low-growing sages (Artemesia filifolia or A. frigida).

cold-hardy low-water dragons blood sedum
Dragon’s blood sedum has such a rich, red color. It’s a cold-hardy perennial groundcover perfect for xeric rock gardens.

Flowering Perennial

Red hot pokers (Kniphofia uvaria) are workhorses in low-water, cold-hardy gardens. Also called torch lily, the plans resemble a lily in its foliage. But the tall, torch-shaped blooms with red and yellow tubular flowers can last for weeks. Hummingbirds visit the flowers, and birds often visit spent blooms. Meanwhile, the plants form clumps in the ground that spread. Many gardeners use them as fence borders, and they’re one of the easiest cold-hardy perennials to care for in a low-water garden. Other low-water, cold-hardy flowering perennials are Dusty Miller and Gayfeather, to name a few.

kniphofia red hot poke low water perennial cold hardy
Imagine a wall of red hot poker blooms filled with hummingbirds. And they spread, so you can add more or share them with your friends! Photo courtesy of Diana Reavis of Plant Select.

Deciduous Shrub

The Utah serviceberry (Amelachier utahensis), also called a shadberry, is a low-water shrub that drops its leaves in winter but only after turning several gorgeous colors and producing berries for birds and other wildlife. It is closely related to the Western serviceberry (A. alnefolia). It’s native to low-mountain or high-desert areas of Utah, New Mexico and along most of the Rocky Mountain region. We purchased a stock of bare-root serviceberries that we’re raising in a protected area near the river so they need less water while getting established. Other low-water deciduous shrubs cold-hardy in high deserts or intermountain regions are the Leadplant, Fernbush and Sumacs.

service berry fall color
This bare root serviceberry already has gorgeous fall color in its first season. As it grows, it also provides food and shelter for birds.

Evergreen Shrub

Mahogany (Cercocarpus) uses very little water and has an interesting, desert-like look in the landscape. The evergreen shrub can adapt to temperature extremes up to 100 degrees F, and is cold hardy to 20 degrees below or more, depending on the type. Curl-leaf mountain mahogany (C. ledifolius) can get large if left untrimmed, but the little-leaf variety only grows to about 8 feet tall. Both do best in full sun and with little water. Other cold-hardy evergreen shrubs that work well at high altitude are Damianita and Cotoneaster.

littlelead mahogany
Littleleaf mountain mahogany offers evergreen foliage and shelter for birds. This Cercoparpus intricatus is from Plant Select in Colorado, photo by Pat Hayward.

Tree

The alligator juniper (Juniperis deppeana) is one of few junipers that I really love. That’s because I’m allergic to juniper pollen, as are many people who must live around the plants in areas where the air is plenty dry. Junipers thrive in poor soil and low water conditions and they’re long-lasting evergreen trees and shrubs. The alligator juniper is named for its reptilian-like trunk, making it more interesting in the landscape. Many also have multiple trunks. Alligator junipers do well in elevations between 4,500 and 8,000 feet. Lots of other low-water trees fare well in cold climates, including the Netleaf Hackberry, Mexican Elder and Gray Oak.

alligator juniper
I love the bark of the alligator juniper tree.
junipe rberries
Birds love juniper berries. It looks like a few already munched on these.

 

Favorite Low-water Plant: Smoke Tree

Fall’s cold and wind have obliterated most of our foliage, or at least relocated it from limbs to patio and ground. But one small tree hangs in there with a full canopy of greenish-burgundy leaves. The smoke tree (Cotinus coggygria) is one of my favorite trees for fall and year-round color.

cotinus coggygria smoke tree in fall
The redbud and most other trees are suddenly bare, but the smoke tree (Cotinus coggygria) is full and colorful!

In fact, our tree held on to many of its crispy gold leaves all winter last year. Then in spring, new green foliage emerged. But the tree’s seasonal colors, which changed from greenish blue to deep burgundy or purple, to gold, are only part of its charm and drama. It also sends out puffy seedheads that resemble — and smell like — smoke. The pinkish seedhead clouds, which give the tree its name, usually appear in mid-summer here, but the timing varies depending on conditions. Regardless, they remain attractive for weeks.

smoke tree with winter foliage
Last March, our tree still had crispy gold leaves on it, and these deer hadn’t bothered to munch on them.

Caring for smoke trees

So I love how smoke trees look, but here’s what really seals the deal for the New Mexico xeric gardener: The Sunset Western Garden Book says the tree is “at its best under stress in poor or rocky soil.” OK, I have lots of that. And it can tolerate some drought. When temperatures hover above 90 degrees F, a deep water every couple of weeks helps get it through the hottest part of summer.

The other attractive feature of smoke trees for xeric gardens is their versatility. While the trees are starting, gardeners can shape them into small bushes or short trees, depending on the location or preferred look. C. coggygria typically has multiple small trunks. Ours was trained to a small tree shape, which still works well in a large rock garden because it only grows to about 15 feet high at a rate of about a foot a year. You can train it for light shade, or as a low, bushy foundation plant and home for birds.

Here's our tree right now, full and colorful even though the seedheads are mostly faded.
Here’s our tree right now, full and colorful even though the seedheads are mostly faded.

Until established, smoke trees might need a little more water and application of some slow-release fertilizer in the spring. But since it prefers poor soil, the tree needs no more than that once it’s on its way. And if you’re shaping the tree, Judith Phillips recommends that you cut back or stop fertilizing once you begin those pruning cuts. You can add some mulch to save water and cool the roots, but since the tree loves rotten soil, there’s no need to add organic matter. And if you add mulch, be sure to keep it away from the trunk. The tree can thrive in full sun or partial shade. Suckers will begin to show up around the base of the trunks; you can just pinch or cut them off to send energy back up into the main trunks.

large smoke tree with seedheads
Here’s a smoke tree in full bloom amid iris in late spring at the Hondo Iris Farm. It’s in wetter and slightly warmer conditions than in our zone 6B rock garden.

Smoke trees are subject to verticulum wilt and leaf roller mines in early summer. We also had to remove about 40 io moth caterpillars from ours this year because they were stripping entire branches. But those stinging nasties were making their way around all the small trees near the house.

More about smoke trees

The C. coggygria varieties do fine in USDA zones 5 through 8. The purple varieties look great on their own or as a bush planted near a silvery conifer or perhaps with an artemesia or gray santolina planted in front of them.

smoke tree leaves and blooms
Smoke tree leaves and seedhead behind them. The color changes throughout the year and even depending on the light during the day.

The C. coggygria is sometimes referred to as the European smoke tree. Another species of smoke tree called C. obovatus is called the American smoke tree. It is slightly larger and has bigger leaves, but has similarly striking seedheads. The Dalea spinosa (Psorothamnus spinosus) also is called a smoke tree. It is a grayer tree native to Southwestern low deserts.

How To Water Mature Trees

When drought strikes, it’s tempting to cut back on watering of established trees or stop watering altogether. And maybe water restrictions in your area force your hand. I hate to see it happen, because trees can offer many benefits – most notably shade for homes to cut down on energy use, and shade for other plants to keep them alive and in need of less water. Of course, you can’t beat the enjoyment of sitting under the shade of your favorite tree. I won’t even get into how depressing it is to see dying trees in front lawns…

Ideally, your lawn has only native trees, and especially xeric varieties. In that case, the trees adapt to conditions more easily. Some survive on rainwater alone, but most need a deep watering about once a month during the heat of summer.

desert willow tree xeric
The desert willow (Chilopsis linearis) is a perfect xeric tree for warm to hot desert climates. This one is from a Tucson, Arix., garden.

To water your a mature tree that requires irrigation, avoid a common mistake — watering only near the trunk. Trees do not have tap roots, but instead have a root system that extends out from the tree, more or less mirroring and extending just past, the tree’s branches above. So, when you set out your hose or set up a drip or soaker system, begin near the trunk, and then work your way out to the edges of the tree’s canopy. Scroll down in this handout on caring for trees from Colorado State University for a photo of a soaker hose layout.

To water deeply, you have to water slowly. That means setting your hose or irrigation system to deliver the water at a lower rate for a longer period of time. To reach the roots, the water needs to penetrate the ground to at least 12 inches. If you’ve ever seen roots growing at ground level, they’re probably doing so because the tree is receiving too little or too shallow watering.

Don’t dig a hole around the tree to help get water to go down deeper. The hole allows air in and dries out roots!

If possible, avoid using a sprinkler to water trees. In addition to producing shallower roots, the sprinkler wastes water by dispersing it into the air, where it evaporates. And some trees are subject to leaf diseases from constant watering. The only time I ever spray a tree or bush is if it has aphids, and I give it a fine-water spray in early morning to wash the aphids off.

If you can’t reach a tree with your hose, you can drill a few holes in a 5-gallon bucket and carry it out to your tree. The water will flow more slowly through the hole than if you pour the water on the ground. Move the bucket out and around the tree’s base with each refill.

apple tree along river.
This apple tree is hard to reach with the hose, but we don’t water it because it is along the river bank and the roots take up plenty of water. This year, it had twice as many blooms and may give us some fruit. Trees can help preserve water sheds.

If you want to save tap or well water, reuse! Direct roof water to a tree using the downspout and a dry river bed. Save shower water in 5-gallon buckets (with no holes – you have to get them outside!) but only use the water that flows while the shower warms up, not any soapy flow.

If you have other clear water to dispose, such as kid or dog pools, empty the water onto tree roots instead of a random place in the yard.