How Heat Affects Plants

When it gets hot for a day or two, plants can wilt and require some extra attention. That’s pretty easy to understand. After all, I spend less time outside in the heat of the day because I wilt. I also drink more water. After more than a week of temperatures hovering near or above 100° F, our plants are showing other signs of heat stress that we less often consider.

jimson weed datura new mexico
Jimson weed, or datura, loves heat and drought. Then again, it does have the word “weed” in its name.

You would think that living in the Southwest and having mostly xeric plants means plants can tough it out dor a few hot, dry (windy!) days. That’s partially true. But these temperatures are way above normal, at least for an entire day/week and more. Normally, July 1 marks the beginning of monsoons, where clouds build and drop at least some rain in the afternoon, giving the plants and me a break. Not this year. And it’s causing problems for nearly every living thing in our garden. Here are some reasons why:

Heat can reduce bee populations

We noticed about midway through our current heat wave that we seem to have fewer bees in our garden. Of course, I thought I was imagining that. Nope. Bees are especially sensitive to temperature and its regulation. Temperature particularly affects young bees, which are important for keeping colonies going. They tend to keep their hives at 95° or lower, and stress when the temperatures exceed 98°. Bees also need water, and we’ve had two weeks with no measurable rain and consistently high temperatures, even for our evening lows. Here’s a great explanation from Tufts University on how honey bees keep cool (and warm). Despite the fact that we have plenty of flowering plants for bees beginning in spring, the population is lower this summer. I was pleased to see a few survivors on our lavender this weekend, but this is a brand new worry!

bee buzzing on lavender stalk
Lavender loves dry heat, and bees love lavender, so there’s that…

Lack of flowering or fruiting

Those bees! They also help pollinate our ornamental plants and especially our vegetables. So, there’s one concern in heat. But I recently was reminded how heat also affects flowering and fruiting. It turns out that pollen loses its effectiveness in high heat. Even though we’ve hit the 100° mark before, I can’t recall it lasting for days and weeks since we’ve been growing tomatoes and other edibles in New Mexico. What’s more, drought lessens the chance that pollen can stick to a female flower.

tomatoes green on plant
These tomatoes got started before the heat wave, and I think the plant is doing all it can to keep them nourished.
Another plant is failing to produce. I'm hoping there's still a viable tomato behind each dried up bloom.
Another plant is failing to produce. I’m hoping there’s still a viable tomato behind each dried up bloom.

Wilt

This is the heat issue we best recognize – leaves wilting on a hot day. Plants “sweat” to cool themselves like we do. With transpiration, water travels up from the roots and to the leaves, where it evaporates through tiny pores under the leaves. So on a hot, dry day, the soil, roots, and entire plant dry out more quickly. Add some wind just for fun, and a plant can wilt or stress. Plants can take more water, but only up to a certain point. Some plants have plenty of moisture and experience what’s called “incipient wilt” during peak heat each day. If they recover by morning, the plant probably is getting plenty of water.

yellow squash leaves wilting in heat
The big leaves on our yellow squash tend to wilt each day, but the plant looks healthy when it cools.

Sunburn and sun scald

Plants can get sunburned. The sun can scorch leaves of plants that typically need a little more shade or lower temperatures. And many plants can burn on super-hot days. The sunburn often leads to brown spots or browning and dying of entire leaves. Sunburn of a few leaves shouldn’t be a problem, but a sign to shade or move a plant if possible. Sunscald is similar damage to bark in high temperatures.

When weeds and wildflowers wilt, it's just too hot and dry. We have some that also look burned up. Woohoo!
When weeds and wildflowers wilt, it’s just too hot and dry. We have some that also look burned up. Woohoo!

Entirely new or different insects

Aphids, which can be controlled organically, tend to love cool, moist weather. Every type of insect is different, but they’re cold-blooded creatures. Insects can’t internally regulate their temperatures, so they rely on what’s happening in their environment. I’m certain that both weeds and insects change each year depending on weather. Cabbage loopers and leaf miners like heat. Ants? Don’t get me started. And dreaded grasshoppers thrive in drought. When a plant already is stressed by heat or drought, it’s more vulnerable to insect damage or insect-borne diseases.

grasshopper in patio chair
Sure, grasshopper, pull up a chair. In fact, take the shady spot. I’d rather see you resting than eating on our plants.

Some plants adapt better to heat than others. However, young plants still might need more frequent watering in high heat. That’s the part that’s getting to me most. We have some new plants we put in the ground not long before the heat wave hit, and they’re struggling. We’ve even had to water a few xeric and waterwise plants that typically thrive with no water at all. It’s all part of the fun of gardening in the Southwest, I guess. See my previous post for tips on helping plants survive extreme heat.

Add Evergreens to Your Low-water Garden Plan

Most of my gardening friends have started seeds and marked up pages in catalogs because when spring is in the air, we get excited, even impatient, to return to the garden. It’s easy to plan for spring and summer bloomers, but also helpful to think ahead to next winter, when blooms fade.

snow on evergreens
Winter can be pretty in any garden, and snow on evergreens… gorgeous.

Evergreen shrubs and trees add visual interest, homes for birds or other wildlife and privacy in winter. Evergreens are particularly helpful in dry or cold climates. Choosing an evergreen for the low-water landscape does not confine the gardener to conifers. There are many choices to fit nearly any xeric garden design or location, such as santolina.

santolina
Gray santolina is evergreen — or evergray — and produces bright yellow flowers in summer.

Saltbush (Atriplex canescens) Saltbush, also called four-wing saltbush, is a native plant of Western states. Although its colors aren’t bright or striking, saltbush is an unusual and interesting plant. Native Americans once used the stems for fuel and made yellow dye from the plant’s leaves. Although I haven’t tried the seeds, they are edible, and we once saw locals gathering the seeds when driving south of Albuquerque. When the seeds emerge, they make a gorgeous contrast to the foliage, which is more silvery green. And they’re swirly and paper-fine to the touch. Saltbush is native to alkaline soils and salty high deserts.

four wing saltbush
The four-wing saltbush is a native that looks terrific in a natural landscape.

Boxwood (Buxus). Boxwood is surprisingly drought tolerant if given some shade or in a northern exposure, deer resistant and easy to care for in the lawn. In fact, the plant is subject to fungal disease, but when panted with the crown about an inch higher than its position above the soil in its nursery pot. Well-draining, slightly alkaline soil also helps, which makes it a perfect evergreen shrub for most of New Mexico. Most boxwoods grow in zones 5 through 9.

petite pillar boxwood
Monrovia’s petite boxwood is even more versatile in a container. Photo by Doreen Wynja for Monrovia.

Although boxwoods don’t need substantial attention or trimming, gardeners who enjoy pruning will love shaping these plants to match the landscape. A new boxwood from Monrovia, Petite Pillar Dwarf Boxwood, has a naturally column-like form, which sets up easy maintenance for the gardener. It fits perfectly in containers, but requires regular watering, especially in heat.

agaves mass planting
Agaves surround this tree at Tucson’s Desert Botanical Garden.

Succulents. If they’re hardy in your zone, succulents can provide year-round interest, especially in xeric gardens or along walkways or fences. Their shape adds a unique look to winter gardens. For example, the agave (Agavaceae) is like garden art with its upright, sometimes symmetrical design. The plants are long-living perennials, and some varieties are hardy down to zone 5. With about 300 species to choose from, gardeners are sure to find one that suits their design and zone. Although they grow slowly compared with shrubs, agaves need a little room to expand. Set off the plant’s color with a contrasting ground cover such as speedwell or purple iceplant for more summer color.

blue agave
These blue agaves (Agave parryi, or Parry’s agave) add texture and color to our winter garden.

The aloe vera provides a similar look, although the leaves are fleshier and more upright. The plant is not as cold hardy as agave, and needs to be outside only in climates with warm winters, no lower than 40 degrees at night.  Aloes also add value to your garden. We’ve used aloe directly from a plant to soothe sunburns.

Yuccas also are easy to grow, and their slimmer, spear-like leaves look brilliant all year long. They’re also a diverse xeric plant; you can choose a variety that’s bushy and full at the bottom or more open and fanned out.  Check the variety’s mature height when purchasing to make sure it won’t get too tall for the location you choose. Some varieties, such as Joshua Tree, grow to 15 to 20 feet high. After a few years, yuccas produce summer flowers on tall stalks from the plant’s center.

Caring for these succulents is simple. They need some sun, but can burn if exposed to too much direct sunlight. And the only problems with the plants typically come from overwatering. Avoid watering these succulents in winter, or the plant can get root rot.

Lots of evergreens grow nearby, including the pinon.
Lots of evergreens grow nearby, including the pinon.

Conifers. Piñon pines (Pinus edulis and a few others) are native to New Mexico and Arizona. It’s more like a rambling, tall shrub than a tree, easy to care for and used to semi-arid regions. The seeds, or nuts, are edible.  Icee Blue Yellow-wood (Podocarpus elongates ‘Monmal’) has stunning blue foliage in winter, but only in southern climates (zones 9 through 11). It has a thin, conical shape when mature and can be trimmed into classic Christmas tree shape, a nice touch for a warm winter garden. As with all xeric plants, Icee Blue needs a little extra water until established, then gardeners can cut back. Alligator juniper is a terrific bird shelter that has interesting bark along with evergreen branches.

podocarpus icee blue
Icee blue yellow-wood needs little water once established. Photo by Doreen Wynja for Monrovia.

Icee blue also is the name given to a spreading juniper (Juniperis horizontalis ‘Icee Blue’). I’m not a big fan of juniper, mostly because of allergies. But the plant can provide evergreen groundcover in a low-water lawn. Icee Blue is hardy down to zone 2, and prefers full sun. If controlled with trimming or planted in mass plantings, junipers are a low-water alternative to shrubs and other groundcovers. If you want to cover an area of ground quickly with a plant that requires little maintenance or water once established, check with your local nursery for a juniper that can survive your winter lows.

The low-lying juniper to the right of our budding apricot was in the garden when we moved here and produced tiny berries.
The low-lying juniper to the right of our budding apricot was in the garden when we moved here and produced tiny berries.

 

Use Plant Finders and Identifiers to Plan Your Xeric Garden

So you want to plan a xeric garden, or begin converting your garden to a low-water design. It can seem overwhelming at first. You can call in a xeric landscaping professional, especially for a big job. But to make small changes, you mostly need help finding good replacements. For example, what’s a low-water plant with red blooms that enjoys a mix of sun and shade?

Enter a plant finder. Most let you select any number of fields or filters, and many also provide searches in both common and botanical names.

deep red iris bloom
OK, so we all know this is an iris. That’s all I know so far, because it bloomed for the first time a week ago. I just had to include a photo of it in some post.

Plant identification tools also help, but I find they work best if they have several photos – at least one close-up shot of foliage and flowers, and another full shot of the plant. You’ll use identification often if you pay attention to plants as you drive around your town or neighborhood, or spot a great specimen in a friend’s lawn. Your friend may have no idea of the plant’s name. Here is a short list of plant ID and plant finder sources:

Identify Plants Online

One of my favorite Southwest sources for xeric and high-desert selections just added a plant finder. Plant Select provides a dozen fields, including water needs and deer resistance, important considerations for me.

plant Select plant finder
Screen shot of the Plant Select plant finder. It’s got plenty of filters to help you plan your xeric garden.

The National Gardening Association also includes an extensive plant finder on its site, which lets you select USDA zone.

Finally, for a more scientific approach, go to the USDA site. I’ve had more luck there with the scientific name, but that’s pretty easy to find with a good online search of a plant’s common name.

Plant Identification Apps

I love plant ID apps, because I always have my phone with me in the garden. The problem is tracking down good one with Southwest plants. So far, the only one I’ve found that’s free, dedicated to xeriscaping and accurate for my area is SW Plants. It’s from New Mexico State University. If anyone out there knows of a better one for xeriscaping, I welcome input!

SW plants plant finder
SW Plants app on my phone. The search works well for the 750 xeric plants included.

 

SW plants app zinnia photo
The photos in the SW Plants app are pretty nice, but small on my phone.

In addition, Audubon has apps for wildflowers and trees. Otherwise, as in most cases, content comes from and focuses on the northeastern and southeastern portions of the country…

Remember Books?

We have some gardening books. In fact, a shelf of our sitting room is lined with them. And I often can identify a plant by consulting several of them. Sure, sometimes a Google search is quicker, but it’s too hard to rely on images posted by people using common names to identify a plant. So it might be a good place to start, but books local to your area are best. My favorites for this area are the Sunset Western Garden Book (keeping in mind that Sunset assigns its own zones) and Judith Philips’ New Mexico Gardener’s Guide. Any book on native plants and wildflowers for your state or region is priceless as well.

shelf of gardening books
Got gardening books? Many books have older, dull photos or illustrations, so check out photos before buying.

Keep Current Catalogs

Catalogs are excellent resources, especially for planning your garden each year! We save a few of the most recent from our favorite suppliers, and often can either identify a plant we already have or see somewhere nearby, or plan our garden each spring with the catalog’s help. They have the best photos, if you’re willing to spend time leafing through pages. It’s one of our favorite activities with coffee on spring mornings!

I recently helped a friend identify a gorgeous wildflower she spotted on a hike in Los Alamos, using a combination of our catalog from Plants of the Southwest and an online search. Our other favorite catalog arrives regularly from High Country Gardens.

Buying Garden Plants: Big-box Store Vs Local

A few days ago, I wrote a post about the Plant Select recommended and new introductions for 2015. Plant Select, up in Denver, evaluates how well these plants perform at high altitude and with less water, and also whether the plants are native to North America. And they encourage gardeners to support local nurseries. I couldn’t agree more.

Let’s take a look at the reasons why it’s often best to buy plants from local nurseries, along with reasons why it’s sometimes better to purchase at the Big Box store.

First, supporting your local nursery is the same as supporting your local grocery store, electrician or restaurant. It’s neighborly and the right thing to do, especially if you also own a local business. The major reason for gardeners to buy locally is to ensure they find native plant selections for their area. I can’t tell you how many times I have wandered into a chain store’s nursery area and shaken my head in wonder. It’s obvious that the store’s buyers know little about New Mexico, or perhaps lumped the state together as one zone, or maybe with Phoenix. That’s crazy! Some plants wouldn’t make it here, or might work as an annual, and others use too much water.

When buying from local shops run by people who live in your community and who usually are quite knowledgeable, you may have less selection, but what you lack in quantity, you gain in quality. I’m not necessarily saying the plants are always better quality – we’ll get to that. But the plant selection likely is confined to native plants for your area, or at least to plants most likely to succeed in local gardens.

 

Native nursery in Tucson, Ariz.
Shopping at a local native nursery in Tucson, Ariz.

So, when do you buy local and when do you buy from big chains? It’s a matter of personal choice, and every town is different. So this is based purely on my opinion and experiences: If I want a lot of annual flowers to fill a large bed or several containers, I might be more likely to buy those from a chain. I don’t need the quality of a longstanding perennial, and I want some variety. Chances are most annuals can make it through the season. I save money that way.

For a solid perennial, especially in a unique situation and one I’ve never grown before, I would head to the local nursery for advice and a quality selection. Chances are I will find staff with good knowledge of my zone and climate and how to care for the plant. I’ll pay more, but that’s OK if it’s a good quality plant, especially because I’m also getting the right, native plant and some free advice thrown in.

Some local nurseries grow their own stock. That also can be good, if they know what they’re doing and care for their plants well. But if you have a few bad experiences with a nursery’s plants and are paying higher prices, try another local garden source or seek advice from local Master Gardeners and extension offices and find your plants elsewhere, maybe in a nearby larger town, but still from an independent nursery. You can’t beat word-of-mouth recommendations when it comes to nurseries. They all look awesome as you drive up!

The Good, the Bad and the Ugly: Weed or Wildflower, Part 2

Nearly a year ago (in May 2014), I wrote a post about the fine line between weeds and wildflowers. The gist of the rant was that our rock garden and entire property was being invaded by a lovely flower called yellow alyssum (Alyssum alyssoides). It’s a little earlier in the spring, and even yellower!

First, the good. If you love early, yellow blooms, this is a pretty little flower. It looks pretty up against a rock or under a red rose, perhaps. Notice I said “it,” as in a single plant. More on that in the ugly portion…

yellow-alyssum
Yellow alyssum sprouting from rocks in a New Mexico rock garden.

Now for the bad: This little spreader has cropped up throughout the garden, and we’ve pulled up a few, though I surrendered long before my husband. He has much more patience, though he hasn’t yet tackled the entire garden. Because he wouldn’t get halfway before he had to start again.

alyssum-prickly-pear
Yellow alyssum growing between pads of prickly pear cactus.

If I had any doubt last year about alyssum’s classification as a weed, at least in this setting, I have no doubt now. And that’s the ugly part. Despite our best (nontoxic, of course) efforts to control this little bloomer, it has taken over every nearly every surface and begun spreading to neighbors’ lawns as well. I have no idea how it started; it came with the house!

alyssum weed
Yellow alyssum as invasive weed in southeastern New Mexico.

Having called it ugly, I have to admit the lawn is really pretty when the sun hits it just right early and late in the day. And we are doing our part ecologically, because the bees swarm all over it when the sun shines. The dogs and deer must tread carefully.

alyssum and deer NM landscape
OK, I admit that the alyssum looks pretty here from a distance. But play “Where’s the Alyssum?” and you’ll spot it everywhere. And what exactly are those deer running from?

As for last year’s fear about the alyssum choking out summer grass, we still had a green lawn come summer. We don’t know if the flowers delayed the grass coming in, but I have a feeling they did. And I am frightened to think what will happen as it takes over, reseeds and multiplies. Meanwhile, I need to research medicinal properties of alyssum flowers or something. Maybe I could make some money?

UPDATE April 6, 2015: A few days after posting this, we headed east to visit relatives, through Roswell and almost to the Texas border. Guess what we saw growing in the worst possible conditions along roadways nearly the entire trip? You guessed it! And it was in my in-laws’ lawn and their neighbors’ yards too. My mother-in-law said she has seen it for years and knew it as a prairie wildflower. I give up and accept this invasive plant as a prairie wildflower … for now.

Four low-water Container Plants

I love pots! Actually, I love any kind of container that will hold a plant. We’ve been known to grow herbs in a claw-foot tub and annuals in an old washer. When you grow plants in containers, you increase your flexibility – you can move the container with the sun (maybe not the claw-foot tub so much…) and have color in a shady location by your front door. You also can practice “flower arranger,” creating a few new containers with each season’s annuals, or putting together a group of perennials you can keep outside all year or winter over.

Here are a few favorite low-water plants that grow well in containers:

Verbena (Verbena tenuisecta). Verbena species vary, but the warm-zone, low-water species can grow with very little water. They came up through the gravel pathways in our rock garden, re-seeding from previous years. I’ve planted small varieties of red, white and rich purple verbena in containers. Once established, verbena will spread and using it in container groupings helps tie them together or add pops of color. Verbena requires no deadheading, though removing spent flowers can prolong the bloom period, which usually runs from spring through frost, depending on your zone.

purple verbena
Verbena looks great alone or as part of a group planting. This magelana violet variety, and the photo, is courtesy of PlantSelect.

Chocolate flower (Berlaniera lyrata). Great in a rock garden or container, a chocolate flower always pleases. And in case you’re wondering, it really does smell like chocolate. I ought to know. Anyway, chocolate flower is a wildflower that produces delicate, daisy-like flowers with a light, almost red, center. Its leaves are a pale, almost silvery green. It’s extremely drought tolerant. Planting it in a container means you can enjoy its scent right on your patio or outside an open window.

chocolate flower
I love the chocolate flower buds; they’re delicate and different. Image courtesy of PlantSelect.

Rosemary (Rosmarinus officinalis). Rosemary is equally pleasant smelling and actually edible! I grow it every year in a container, and have several plants growing as ornamentals in our garden. It has evergreen foliage, so if you live in zones 6 to 8, you probably can keep it alive all year in the garden. In zone 6, it also might make it in a container, though I’ve had creeping rosemary burn from cold or snow even in zone 7. So either protect your container or bring it in, depending on the hardiness of the variety you choose. But back to enjoying rosemary! Plant it all alone near your kitchen for easy fresh cuttings, or in a group container. And if you decide not to take cuttings for cooking, your rosemary might eventually bloom lovely lavender colored blooms. At any rate, put it where you can frequently walk by and just rub your fingers over the leaves.

Rosemary_pot
My rosemary has survived sub-freezing temps so far up against the south side of the house. It still smells terrific, even after the wind blew leaves all over the container.
Creep_rosemary
Bees love this creeping rosemary, which requires little to no water in a container or landscape. This is all one plant; we had to cut some away in the middle after it burned. We should have knocked the snow off.

Ornamental grass (try blue fescue, silky threadgrass, or blue avena). Who says a plant has to flower to look great, especially in a container? I love adding a spike of height and texture with a grass, often in the center or back of a container full of colorful annuals. Most grasses need less water than flowering plants, and they look great blowing in the wind or adding height to a container, especially one placed up against the house. Many of them even flower. Just be sure to check the tag to see how high the grass normally grows before making your purchase.

And remember that plants always need a little more water when you first plant them, in extreme heat and when in containers than when in the ground. Containers usually dry out more quickly than ground soil – how much more depends on the container, soil you used to fill it and the location. And containers are microclimates, which means they might place your plant in colder, warmer or drier conditions than you realize.