10.12.10


Cold Weather Problems

Well, it is that time of year again when we see the roller-coaster weather ride of hot muggy weather interrupted by fast-arriving cold fronts with temperatures near frost, followed by weeks of warm sunshine and dry days. This up and down style of weather wreaks havoc on some plants, especially those with tender foliage, or those plants prone to damage from drying winds. It does not require freezing temperatures to fatally damage plants; some plants can be mortally damaged at temperatures below 40 F, and there are species that show severe damage even at 45 F. There are legion stories of Breadfruit trees showing discomfort at 55 F, although I have not seen this personally.


Cold damage on Aglaonema


Cold damage on Kerriodoxa palm




Cold Damage on
Dieffenbachia


Early this year, Florida saw some of the longest cold weather periods in recent history. The deadly combination of strong dry winds, unusually cold weather ( under 40 F for days at a time), and the length of the cold period resulted in a large amount of leaf and plant loss. While many plants can withstand short periods below 32F, rather few tropical and subtropical plants can withstand such temperatures for days on end. With this scenario, several processes happen, setting many problems into motion over the next 12-18 months. The soil temperatures dropped to such a degree that plant roots stopped moving water from the soil to the foliage. The end result is that plants desiccated, even if the roots were quite wet. Some plants simply died back, some plants lost their foliage due to extremely dry air ( less than 30% humidity for days), and some died of secondary fungal infections. Even 12 months after a prolonged cold episode, plants can still show the damage from cold weather. It takes a lot of patience to recover plants from such episodes, and one must be diligent in keeping up the program to re-grow foliage and roots. It also helps to know whether a plant is actually dead or just "hiding" from the cold. Many gingers and aroids had their foliage frozen off, but 6 months later the plants "woke up" and grew back almost as if nothing had happened.

One of many tactics I've seen recently is to use a dilute hydrogen peroxide solution as a  surface cleaner to reduce fungi and bacteria on dying foliage. There are several commercial preparations such as Zero-Tol and
other products based on hydrogen peroxide. While the off-the-shelf variety of peroxide is usable, it must be diluted to avoid damage on the plants. Try a small area of a leaf to check for bleaching or damage before using it on larger areas.

One of the most important tactics for cold-weather recovery is to wait until the cold weather is well passed before thinking about trimming any damaged branches. It is commonplace that trees will lose leaves and stay leafless for up to 6 months after cold weather. Trimming leafless branches too soon after a cold episode can damage a plant more than leaving the damaged branches on the plant. I have seen instances where trees magically sprout leaves up to a year after cold damage.

Even tropical palms can regenerate a damaged spear leaf many months after cold damage. Many growers pour copper-based fruit tree spray into the crown of a palm to control bacteria and fungi in the center after cold weather. In many cases, the palm has the energy to regenerate a new spear leaf, but the fungi and bacteria present after cold weather damage the leaf  faster than the palm can grow a new leaf.

The overall advice from most arborists and growers I know is to wait until mid-summer to trim trees. It's OK to trim brown leaves off any time, but leave any leaves with any level of green in them. The plants will need all the help they can get.

Craig Morell
Pinecrest Gardens   


















     

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