Anxious to replace all those plants? Here’s what you need to know.
Looking outside my windows today, I can see signs of a Texas spring beginning to shine. The sun is more-often seen, warming what it touches. The days are beginning to last longer now and birds are singing –typical signs that spring in Texas will be here soon.
There is something different though. Texas landscapes—normally marked by the new growth of buds and blooms—are brown and bare. On a seemingly beautiful day like today, there is absolutely no other indication that the entire state recently found itself dealing with historic winter weather, record subzero temperatures, a failed power grid, and an unstable water supply mere weeks ago, until you begin noticing how dramatically vegetation has been affected.
What does this mean for projects? What should clients do and not do? Continue reading to find out.
What is the polar vortex?
According to weather.gov, the polar vortex is a large area of low pressure and cold air surrounding both of the Earth’s poles. It always exists near the poles, but weakens in summer and strengthens in winter. The term “vortex” refers to the counter-clockwise flow of air that helps keep the colder air near the Poles. Many times during winter in the northern hemisphere, the polar vortex will expand, sending cold air southward with the jet stream. This occurs fairly regularly during wintertime and is often associated with large outbreaks of Arctic air in the United States. What is different about this polar vortex is the duration of sub-freezing days (4+ days for many).
How will it affect vegetation in Texas?
The short answer is, we don’t know exactly. Not yet anyway. Not all freeze damage is readily apparent. Non-hardy plants will show damage as soon as they thaw, however, some of the marginally hardy plants may take weeks, months or years to reveal damage. Plants may not die until a second stress, like summer heat, hits them.
General Plant Tips:
- Plants, in general, are like any other group of life forms. There will be a difference in health among a species based on environmental factors and general vigor. A stress event like the freeze may kill the weaklings of the group and not damage the strong healthy ones.
- A lot of plant cold hardiness is strictly genetics. According to Greg Grant, Ph.D with Texas A&M AgriLife Extension Service, “Cold hardiness has much to do with the genetics and evolution of a species (Who’s your daddy and where are you from?)”. Non-native imported plants are not well adapted to extremes of cold.
- A well-watered plant will be hardier than a drought stressed plant. The moisture that came with this freeze will help with freeze hardiness by providing an overall healthy condition, but by also insulating the ground so it does not freeze as deep which could affect roots.
- Plants that were perfectly happy for thirty plus years may slowly begin showing damage. This freeze was longer and deeper than any in recent memory.
- Think before you dig. Microclimates are important. The south face of a building serving as a north wind break versus a lawn exposed to the north wind can make a huge difference.
- Some plants, especially the evergreen trees, will suffer from breakage due to ice accumulation that is not freeze damage due to temperature. Although it is part of the effects of the storm, the treatment is different.
As we begin looking more broadly across Texas, we’ve organized tips specific to Hardy Plants, the Borderline Plants, and the Tropical/Semi-Tropical/Non-Hardy Plants.
Let’s start with Hardy Plants. This category includes most native plants and trees.
Deciduous Trees will be especially hardy. They have already evolved a defense mechanism to withstand cold. They defoliate (lose all leaves) and their sap falls so they are freeze tolerant. This includes most of the native and imported trees that we use throughout Texas.
The exception will be some of the exotics from other parts of the world. Some species of Crape Myrtle will suffer some damage and will need to be cut back to the live wood (in some cases that may be back to ground level). Any non-native deciduous trees that had already broken their bud dormancy (Arizona Ash) will be damaged and die back to hardy wood.
Live Oaks and Monterrey Oaks are often thought of as evergreens, when they’re actually deciduous. They just hold their leaves into the spring season when new foliage comes out. There are also variants that are more adapted to the Texas coast that may not be as cold hardy as hill country varieties. Live Oaks were especially susceptible to ice damage and many large limbs broke due to the weight. The broken limbs should be cut off clean and they should heal okay.
Evergreen trees (softwoods) will also be hardy. This includes the majority of the softwood varieties such as pine, fir, spruce. We don’t have a lot of them here because they are more susceptible to heat stress than cold stress. The Junipers that grow around central Texas should be fine, with the exception of ice damage.
Ornamental Grasses will probably recover well. They are also adapted to cold cycle and regrow from roots every spring. They are typically deep-rooted, and as mentioned, the moisture will ensure the ground does not freeze deep enough to damage them.
There is a small group of more tropical grasses like Purple Fountain Grass that will not come back. The others should be cut back as in a normal winter. Clumping Bamboo can be grouped with the grasses and will most likely need to be cut back to hardy wood or to the ground, but should re-sprout from roots. There may be some varieties that do not survive.
Perennials will also do well for the same reason as grasses in most cases. Some varieties from warmer climates will freeze completely (Mexican Heather, some improved Lantanas and some Salvias). In general, it is best to wait and see how far back they die and then cut accordingly.
Native shrubs for the most part will do okay. They may suffer some dieback but should recover.
Wildflowers should be fine. The spring bloomers that have already germinated are adapted to the cold. Any seeds ungerminated should also be okay.
Let’s move on to the Borderline Plants.
Borderline Plants includes a lot of the ornamental shrubs that we use. These plants are exotics brought in from around the world for their foliage or flower but may be on the border of their range in Texas. It is an area that our clients will likely have a large investment in. This is also a group of plants that we, as a profession, have probably experimented the most with. We will likely find that there are plants that did fine for several years, but this freeze was too extreme for them. The best course of action? Wait and see.
If you’d like to test for damage, one way to test is to scratch the bark. If it reveals healthy green sapwood, then there is a good chance the wood is fine, and it will bud out again in spring. If it shows mushy brown sapwood then it is dead and will die back to where it scratches green, if it scratches green at all. Note that a plant may scratch green one day and then turn brown a week later. The damage is not always immediate visible in this group.
This is a variable group that includes some species that will completely die and some that will come back from the ground. It also includes a large group of Agaves that we use extensively. Remove all the mushy foliage, wait until the weather and soil warms up, and see what comes back before removing or replacing.
This is also a variable group. Native vines like Coral Honeysuckle should be fine, and many of the imports will freeze back, but will probably survive. If you have been training ivy up a trellis for years, you’ll likely need to start over. English Ivy and Asian Jasmine will probably brown off and die back but survive. Fig vine, being in the Ficus family, will probably not survive if growing on a wall or will die back entirely to the ground.
Broadleaf evergreens include plants like Azalea, Camelia, Privets, Indian Hawthorn, Pittosporum, and Viburnum that have been imported from milder climates. They have shown hardiness to temperatures into the twenties but will have damage from the most recent freeze. They may be slow to show the extent of damage, so monitor them and see where the spring buds break and cut back to that point. Some may need to be cut back to the ground and some may not survive.
Narrowleaf evergreens include Junipers and will be more cold-hardy than broadleaf evergreens.
Roses vary greatly depending on the type and variety. They should be treated like the broadleaf evergreens and wait to prune them to see the extent of damage.
Turfgrass hardiness will also depend on variety. Saint Augustine grass will show the most damage since it is a southern warm season variety. Bermudagrass will be okay and the Fescees and Zoysias are the most cold-tolerant.
And last, but certainly not least – the non-hardy plants.
This group has not faired well at all, have died, and will not come back. Many palms and tropicals will fall into this group.
There are very few palms that can tolerate temperatures in the single digits for days. The most cold-hardy are the Texas Sabals and Windmill palms. If the crown of the palm is frozen it will not come back. Brown fronds can be trimmed until you can confirm death.
Herbs are not a cold hardy group. They originate in a more Mediterranean climate and will likely not survive. That includes Rosemary in its forms, which is a crowd favorite.
This group includes Bottlebrush, Esperanza, Hibiscus and Purple Fountain Grass. This will also include many succulents and agaves, which we use extensively. Many of these will die back to the ground, but should come back from the crown if it is not damaged, or from suckers (odd branches that have started growing from the base or the roots of the plant but soon becomes apparent they are nothing like the plant planted). Since the ground also froze this year many will not come back from roots.