Hangin' On

January 1, 2020

Perhaps you have noticed the seasonally abnormal appearance of many Oriental maples (AKA Japanese maples).  I am referring to the tan-brown leaves still attached to many central Indiana specimens past New Year's Day.  But do you know why they are still attached?  Allow me to tell you and to explain what additional (after the fact) impact this could have on the plants.

 

The why (the cause) was an extreme low temperature on November 12.  The thermometer plunged to 8 degrees F--the earliest fall date the temperature has reached single digits in Indianapolis.  Only a month earlier the temperature had been in the mid 80s.  Since the fall color change was also late, the record cold killed the leaves while they were turning and before they had time to naturally senesce.  Different species and cultivars, including other than Oriental maples, were more or less affected, but cut-leaved and weeping cultivars of Acer palmatum were especially hit hard--the accompanying photo is A. palmatum 'Emperor I.'  The cold killed the cells in the thin abscission zone at the base of the petiole--the structure that attaches the leaf blade to the stem.  The killing halted the normal hormonally regulated abscission.  During this process the abscission zone becomes brittle and snaps with the leaf detaching.  But, since the process was interrupted, most of the delicate maple leaves could not and did not fall.  The condition of spent and normally deciduous leaves remaining attached to dormant plants is called marcescence.  While normal for some species (e.g., oak and beech), marcescence IS NOT normal for Oriental maples.  Not to worry, the leaves will eventually break free and fall, but for some specimens and some leaves this may not happen until the new leaf buds swell in spring.  Another consequence is that the carbohydrates still in the leaves when they froze were not translocated to the stems and roots for storage.  This deprivation--reduced stored energy--could negatively affect the amount of growth in spring, impacting vegetative or reproductive tissue, or both, or neither.  Time will tell.  The impact could be amplified by previous stress and/or by conditions yet to occur.  Additionally, fertilizer applied in late summer to fall--an ill-advised practice--could stimulate new growth which likely would not have time to harden off, thus making the plant more susceptible to damage by freezing. 

 

The atypical foliated look may trouble you, but I would advise not to try plucking the leaves.  There may be too many, with some to many likely out of reach, and your plucking could inadvertently cause damage to the stems and buds.  Chill.  Simply avert your gaze if the appearance bothers you.  Mother Nature will finish the job over winter and by the time of new leaf eruption in spring.

 

PS  My friend and expert gardener Jay Park reminded me of the heavy snow fall in mid December which weighed down the branches of many plants.  The load was especially problematic for the aforementioned Oriental maples due to the abnormal marcescence which increased the surface area for snow to accumulate.  Some branches at my place were pinned to the ground, but this was not as much of a problem (less likely to snap) for the more flexible branches of most conifers.

 

 

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