Norfolk Island pine

Norfolk Island pine trees were stellar performers in landscapes after Hurricane Ike made landfall in 2008. They are not finicky about soil type and even tolerate salty situations near the beach. However, the downside to Norfolk Island pine trees in landscapes is their sensitivity to cold weather.

WILLIAM M. JOHNSON/Courtesy

The onset of cold weather conditions the past few weeks seemed to have been more stressful to people than to landscape plants.

Despite the possibility of an occasional severe freeze, local gardeners (myself included) still cling to the use of cold-sensitive tropical plants in the landscape. I utilize bananas and other tropicals in my landscape and I do not plan on giving up on them either. Many tropical plants grow well and provide welcome color and texture to landscapes in the intense heat of our summer growing season.

Surprisingly, many tropical plants are more cold-tolerant than we generally give them credit and will tolerate light freezes where the temperatures dip briefly below freezing. But you do run a risk when leaving them out or not covering them on nights when even light freezes occur.

Many tropicals may survive a hard freeze (temperatures in the mid-twenties and below-freezing temperatures lasting most of the night) by coming back from their lower trunk, crown, roots or other underground parts such as tubers, bulbs or rhizomes.

The following is a sampling of recent questions asked by area gardeners on the impact of cold weather conditions on cold-sensitive landscape and garden plants.

Q: I have several hibiscus plants growing in containers. How susceptible are their roots to cold injury?

A: Hibiscus are tropical plants and do not tolerate extended periods of very cold weather. While the aboveground portion of hibiscus may suffer cold injury, most types are root-hardy in our growing area and new growth can be expected to develop from roots and lower stems as the spring season approaches.

However, plant roots in small containers can certainly sustain cold weather injury whereas, under the same temperature conditions, roots of plants grown in the ground will escape cold injury. Roots of plants in exposed containers can be injured by low temperatures and show no apparent damage until the plants are stressed at higher temperatures after the growing starts.

Q: I live in Kemah close to Galveston Bay and I have two Norfolk Island pines growing in my landscape. How cold-tolerant are Norfolk Island pines?

A: The eye-catching, pyramidal symmetry and softly textured, dark-green foliage of Norfolk Island pines growing in local landscapes have endeared it to local gardeners since Norfolk Island pines survived all that Hurricane Ike had to dish out (i.e., saltwater floods and wind). This landscape tree acted the role of that pink bunny rabbit in TV commercials for it took a licking from Ike and kept on ticking. It almost appeared that Norfolk Island pines were invigorated by the ordeal!

Very low temperatures (30 degrees F to 32 degrees F) over several hours can cause the growing tips to die and fall. Temperatures below 25 degrees F can cause severe freeze damage.

As is often the case for freeze injury sustained by landscape trees and shrubs, the full extent of damage inflicted is usually not known until the spring growing season is well underway.

Q: Will January’s cold temperatures eliminate fire ants?

A: I suspect few people are worried about how well insects fare when a cold snap arrives, especially fire ants. I believe in keeping hope alive but when it comes to fire ants the short answer is “NO!” Fire ants are well-established in Texas and have even invaded the lower tier of counties in Oklahoma where relatively cold winters are common. While the unusually cold weather conditions for this time of year can reduce colony survival of small, newly established colonies of fire ants, most fire ant colonies will survive our cold weather conditions.

William M. Johnson is a horticulturist with the Galveston County Office of Texas A&M AgriLife Extension Service. Visit his Web site at http://aggie-horticulture.tamu.edu/galveston/index

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