In February 2011, Austin and central Texas experienced rare winter conditions that even put native plants to the stress test. With a week that saw low temperature of mid teens to near 20 degrees for a prolonged period of over 72 hours where temperatures never got above freezing, this was just too much for some plants to bear. On top of that, the deep freeze followed a healthy rainfall just ahead of plunging temperatures which dropped 60 degrees within 48 hours. During this period, an inch of powdery fine snow fell. Winter temperatures have been periodically running 20 degrees below normals.
With the exception of an approximately 20 mile radius of central Austin in hardiness zone 9a, central Texas lies primarily in Zone 8b. This means that the lowest winter temperature that can be expected based on records is between 15 and 20 degrees, so weather of this kind should not come as a surprise, Even native plants like the Anacacho Orchid (Bauhinia lunariodes) can be damaged below 25 and killed at temps below 20 unless in a protected location. These conditions are even more critical for non-natives in our gardens, where we as gardeners love to push the envelope, take chances, and believe we can adequately protect our plants should hard freezes occur.
OK, let’s look at a few considerations.
- Covering non-native or adaptive plants to protect them in a deep freeze condition still isn’t enough to prevent damage. To minimize damage, covers must be thick, non-plastic, and tied down to the ground to isolate the cold completely. It is better to have a damaged plant rather than a dead plant and such coverings may prevent the latter.
- Plants like cacti, succulents, agaves, depending on species, can survive mid teens in dry conditions only. The addition of moisture to soil or air, and wet coverings is a sure way to kill or severely damage these types of plants. This is why a rainfall before a deep freeze, which we encounter frequently, can be particularly damaging and why soils for these plants must be very well drained.
Agave "Arizona Gold" showing freeze damage even when covered (left), and recovery mode (right)
The core of this plant was undamaged allowing for recovery. Freeze damaged portions were cut off.
- Micro-conditions may exist that determine the fate of a plant in a deep freeze such as protected locations, heavy mulching to prevent root freeze, snow and ice covering which will actually provide insulation to stems and foliage, exposure to wind, etc.
- Knowing and learning about the plants in your garden through research, trials, and documenting outcomes of plant reaction to certain conditions will help the gardener succeed in getting though the harshness of future winter conditions with minimal impact.
- Have an emergency hard freeze plant protection plan in place which will allow you to respond quickly and effectively should weather conditions change for the worse rapidly or unexpectedly. This involves an assessment of each plant and it’s ability to survive and/or what level of protection it will require to survive the predicted condition.
Well, once the damage is done and assessed, there are recovery strategies for your ornamental garden. Having to buy new plants every year is expensive and not the best solution for most gardeners. Here are a few tips and suggestions.
- Plant damage sometimes shows immediately effects but often it is never known until a month or more later - a delayed decline and death, In the case of some perennials that have turned to mush, there is the dilemma of whether to cut off the dead portion of the plant which could act as an insulator during future freezes or conversely could possibly create a haven for disease organisms which could hurt the plant further. I suggest that as long as we are subject to hard freezes (and that is guesswork), that the insulation barrier be left there as disease organisms won’t be a problem at those temperatures, but removed when temperature rise permanently above 40 degrees.
- Don’t be in a rush to trim back damaged plants. If they are unacceptably unsightly, trim back to a point where at least 1” of dead branch is left intact, otherwise, living tissue will be exposed and further damaged, or budding will be stimulated only to be killed at the next freeze. Look for cracking bark, or other telltale signs of die back, or use the fingernail test, nicking the bark to expose cambium at intervals, looking for live tissue, to determine how far back damage has occurred. Often a plant which looks dead, isn’t and that won’t be known until spring initiates new growth.
- In certain plants, if the core hasn’t been frozen, the plant will recover, such as with palms, cycads, agaves, whose growth is one dimensional or from a single source. Many plants will regenerate from root buds, such as Yuccas, and many perennials. If after a month of warm spring weather, a plant doesn’t emerge, you can dig and examine the health of the roots - whether they are alive or gone. In that case, trim off the dead roots or portion of the base and replant. Many plants are late to rise in spring such as Hamelia patens, so be patient.
- If you are fortunate enough to have a greenhouse, cuttings of plants that can be potentially lost during a harsh winter period can be propagated in advance of winter, kept in the greenhouse and planted as replacement plants in spring. This is a particularly good strategy for hard to find plants which would be difficult to replace.
- In the case of Agaves that may have turned to mush, examine closely the base and core of the plant and if still firm and alive, the plant will regenerate it’s form quickly in spring. So called “hardy” citrus may lose all their leaves but will regenerate them in spring. Oleander, Pomegranite, and other semi-evergreen plants will likewise respond after spring pruning.
- Remember to bring all container plants into a garage or similar protected place. Container plants’ roots are exposed to rapid freezing more so than those in the ground where soil absorbs and retains some heat. Only true Zone 8 hardy plants should be planted in containers which can’t be moved.
The worst hit garden in my yard this winter has been the cacti, agaves, and related plants. Accordingly, I have changed my gardening goals for the coming year. I am challenging myself to develop a cacti and succulent garden that will truly withstand mid-teens and Austin winter conditions without protection. That doesn’t mean I get rid of all those plants that were damaged this winter. They will be nurtured back to health and grown in containers so, in the future, they can be removed from the damaging elements as necessary. Slowly but surely, year by year, my garden is transitioning to a sustainable ornamental garden that will survive central Texas extremes naturally.
This is central Texas where environmental and climate extremes are commonplace. The argument for growing native and adaptive plants is based on this fact as these are proven survivors in this challenging environment. Consider transforming your garden more in this direction to avoid the agonies of plant damage and loss each winter. But most of all, don’t despair if your garden suffered considerable damage this winter. Everyone else is in the same boat as the winter of 2011 has been an out of the ordinary season. Life in the garden will return in miraculous ways - it always does.
A great article on the subject of Freezes and Frosts written by Skip Richter, Travis County AgriLife Program Director also is very helpful in understanding the intricacies of winter damage to plants. Check it out.