Most desert landscape plants don’t need covering during normal winter cold. But some die back after a freeze unless protected. If you grow any of these plants, consider covering them if you want them to look their best the rest of the winter.
If you live in USDA hardiness zone 9 (which includes Tucson, Phoenix, Las Vegas, and parts of southern California), the lowest temperatures are typically in the mid-20s. Many landscape plants, especially native plants and mature plants, will come through the occasional cold snap unscathed.
But some common landscape plants are right on the cusp. They’ll survive normal cold temperatures but might die back or sustain cosmetic damage that will be evident until new growth appears in the spring.
If you have any of these plants in your yard, and want them to look their best during the winter, consider covering them when the temperature dips below freezing.
Groundcovers
Lantana (Lantana camara) is widely grown as a flowering desert ground cover. These plants are generally cold-hardy and will survive at temperatures into the 20s. Some hybrids, like Dallas Red or New Gold, can survive down to 10 – 15℉. However, most “shrub” lantanas are prone to frost damage. Once the temperature drops below freezing, their leaves turn brown and they look rather dead until they rebound in the spring.
Trailing lantana (Lantana montevidensis) is another species that grows low to the ground and almost always has purple flowers. It is more cold-hardy than L. camara and survives temperatures down to 10℉. In a mild winter, it will keep its leaves and bloom all winter. You know this plant is flirting with too much cold when the leaves start turning dark green to nearly black. Once the temperature drops below around 27℉, plants die back to some degree but will rebound in spring.
If you see a plant’s leaves turning red, purple, or nearly black,
it’s reaching its cold tolerance limit.
Shrubs
Shrubs form the backbone of any garden so keeping them flowering throughout the winter will make your garden more beautiful. Additionally, keeping these shrubs in bloom provides hummingbirds with much-needed winter sources of nectar.
Cape honeysuckle (Tecoma capensis) is a vigorous South African native that grows as either a shrub or a vine, depending on how you trim it. It will survive temperatures as low as 18℉ but will show some cold damage if the temperature dips below 25℉. If it doesn’t die back, it can be covered with vivid orange trumpet-shaped flowers all year.
Coral fountain (Russelia equisetiformis) is a cascading shrub that can flower all year in mild winters. It survives temperatures as low as 25℉ but often shows some frost damage when the temperature dips below 32℉. Since it’s not a large plant and can flower all winter if not frost-damaged, you might want to cover it to keep the red, tubular flowers available as a source of nectar for hummingbirds.
Mexican honeysuckle (Justicia spicigera) is native to arid and subtropical climates in Mexico and Central America. This plant will survive down to 10℉ but its leaves will suffer frost damage when the temperature drops to 25℉. This is another plant that is a hummingbird magnet when in bloom.
Vines
New vines can benefit from being covered while they are getting established. But once they reach their mature size, covering can be impractical, if not impossible. In extreme cold, you can help your plant by covering its roots.
Queen’s wreath (Antigonon leptopus) is a dazzling vine native to Mexico and Central America. It’s root-hardy down to 20℉ but dies to the ground once the temperature drops below freezing. In locations where there is no frost, it stays evergreen.
Snail vine (Vigna caracalla) is a vigorous semi-evergreen vine with unique snail-like flowers. In frost-free locations, it stays evergreen, otherwise it loses its leaves. It’s native to tropical areas in Latin America and doesn’t like the cold. It shows signs of damage once the temperature drops below 40℉. However, it’s root-hardy down to 20℉ and rebounds quickly in the spring.
Trees
Obviously, covering large trees isn’t possible. If you have a mature tree in your yard, it’s safe to assume that if it made it this far it almost certainly will be OK unless you experience record-breaking cold temperatures.
However, if you have a young tree, you may want to consider covering it for the first few years while you still can for its health and for aesthetics. Here are a few small trees that may benefit from covering while young.
Cascalote (Tara cacalaco) is a small mostly evergreen tree native to Mexico. It has the unusual habit of blooming in the winter when little else does. It is cold-hardy down to 20℉. And while it may show some signs of cold damage below 25℉, it will have no problem bouncing back in the spring.
Mexican bird of paradise (Erythrostemon mexicanus) is a small evergreen tree native to parts of Mexico and Texas. Its lemon yellow flowers bloom much of the year. It’s cold hardy down to 15℉ but can experience some cosmetic damage at around 25℉.
Texas olive (Cordia boissieri) grows as a large shrub in its native habitat of southern Texas and northern Mexico. There’s a reason its natural range does not extend north of the southern tip of Texas — it’s limited by cold. According to the University of Arizona, plants will suffer damage when the temperature dips below 26°F.
If you’re growing this plant as a shrub, frost is not a big concern since you can prune back damaged branches without destroying its shape. But, it’s more commonly grown as a medium-sized ornamental tree, and frost damage is a concern if you’re growing it as a tree. If it gets too cold leaves will drop and stem tips will be damaged.
I see some beautiful trees near me but they are well-established and in protected areas. So depending on your microclimate, Texas olive may survive winters unscathed… or not.
Citrus trees are a special case since every type of citrus tree has different cold tolerances. Lemons and limes are the least cold-tolerant and can suffer some damage when temperatures drop below 25ºF. Young trees benefit from covering. If you grow citrus trees, I suggest you read the University of Arizona’s Protecting a Citrus Tree from Cold.
I lived in a house with lemon and orange trees during the cold snaps of 2011 and 2013 when the temperature dropped to the teens. An outdoor pipe burst, turning my backyard into a skating rink. But my mature citrus trees, which were too large to cover, sailed through unharmed.
Succulents
When you see holidays stocking hats or cups on top of columnar cactus, it’s not always just for decoration. Covering protects frost-sensitive tips.
Mexican fence post (Lophocereus marginatus) is an iconic columnar cactus native to the Chihuahuan Desert that is not very cold-tolerant. When the temperature drops below 25℉, the tips of individual columns can suffer frost damage unless protected.
However, if a few columns get damaged that doesn’t mean your plant is doomed. You can remove the damaged columns, and plants quickly send up new ones that grow fast. And you can use undamaged portions of any columns you remove to propagate new plants.
Totem pole cactus (Pachycereus schottii f. monstrosus) is a weird and unusual columnar cactus. It’s a rare, naturally occurring mutation with a very limited range in the Sonoran Desert. It’s borderline cold-tolerant. When the temperature drops below 25℉, the column tips can suffer frost damage unless covered.
When protecting the tips of cold-sensitive cactus, don’t use plastic cups!
Plastic conducts cold and can cause more damage than leaving tips bare.
Aloe is a genus of succulents native to Africa. Cold tolerance varies depending on the species. For example, medicinal aloe (Aloe vera) is hardy to 26℉ and benefits from being covered, while blue elf aloe (Aloe x ‘Blue Elf’) is a hybrid that’s cold-tolerant down to 20℉ and rarely suffers cold damage. So be sure to know what kind of aloe you have and cover when appropriate. Aloes will reward you in the winter or early spring with stalks of flowers that bees and hummingbirds love.
Firesticks (Euphorbia tirucalli ‘Sticks on Fire’) is a cultivated mutation of pencil cactus (Euphorbia tirucalli), an African native. Depending on your microclimate, planting them in the ground can be dicey since they can suffer damage once the temperature drops below freezing.
Cold, ironically, is your firestick’s best friend and worst enemy. The cold brings out their vibrant color, but it can also kill them.
They aren’t easy to cover since the ends are delicate and easily break, exuding toxic sap. For these reasons, firesticks are often grown in pots that can be moved as needed for cold protection.
Lady slipper (Euphorbia lomelii) is one of the most attractive and unique succulents you can grow in your southwest garden. It has rigidly upright stems — that sometimes twist and bend into interesting curly ques. I generally start mine in pots and then plant them in the ground after a few years since plants become more cold tolerant as they mature. Young stems can be damaged at around 30℉ while mature stems can withstand cold spells as low as 20℉.
Smooth agave (Agave desmetiana) is a medium size agave with smooth, rubbery, recurved leaves. This uniquely urn-shaped plant has a distinctly tropical feel and its leaves are cold hardy down to around 30℉. While it will survive temperatures down to the mid-twenties, it will experience obvious cold damage if not covered and will take some time to rebound.
Do you cover your plants?
Or do “only the strong survive” in your yard? 😉
Please share your experiences in the comments below!
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Author Bio
Deane Alban is the creator of Southwest Gardener. She is a science writer with a bachelor’s degree in botany from the University of South Florida. Gardening is her lifelong passion. She’s been gardening in Tucson for 15 years.
Photo Credits
Vengolis, CC BY-SA 4.0, Wikimedia Commons
Alex Lomas, CC BY-SA 2.0, via Wikimedia Commons
Mountain States Wholesale Nursery
“Euphorbia tirucalli ‘Sticks on Fire‘” by cultivar413 is licensed under CC BY 2.0