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Dallas Morning News - March 19, 2020


Leaf Behavior and Management in the Spring

 

Are your live oaks dropping leaves? Are they in trouble? Dropping leaves, yes – in trouble, probably not. Evergreen trees in general drop their leaves yearly, but usually in the spring rather than fall as deciduous plants do. Some evergreens such as Live Oak may even be bare for a short while. Since the recent heavy leaf drop is worrying people, let’s update my annual leaf management advice.

 

Most deciduous trees like Oaks, Elms, Maples, Ashes, and others drop their foliage in the fall when the days shorten, weather cools and its time for them to rest for the winter.

 


Caddo maple showing marcessence.

 

Semi-deciduous (or semi-evergreen) trees hold some green leaves throughout the winter releasing the dead leaves over a period of time through the winter into spring. Fall color of these trees is spotty and inconsistent. Water Oak, Willow Oak, Canby Oak and others are in this category.

 

Some trees hold their dead brown leaves through the winter and only kick them off as buds swell leading to the new growth for the season. This condition is called marcescence, meaning, "withering but persistent." Leaves on these trees sometimes have pretty fall color but then turn brown and hang on the tree. Others just turn from the start.

 


Canby oak showing its semi-deciduous foliage in winter

 

With marcescence, it isn’t clear whether the dead leaves are clinging to their trees ,or the trees are holding their dead leaves. Theories include deer browse protection, delay of leaf decomposition, and plant immaturity since marcescence seems more common on younger trees.

 


Loquat Leaf Oak showing Yuzuri-ha

 

Maybe the most interesting leaf behavior is called Yuzuriha or Yuzuri-ha. According to Japanese legend, Yuzuriha means that the old leaves are replaced by new leaves in the new season, to "take over" or "take turn." and only dropping after the new leaves emerge, so there is no interruption of the tree’s foliage. It’s noted that the new leaves give thanks to the old leaves for their kind nourishment during the winter. "Compassionate" is a term also used for these trees. Loquat leaf oak is one of my favorites in this category but very hard to find unless you go the annual plant sale at Steven F. Austin in Nacogdoches. http://www.sfasu.edu. That's where I got mine. Also available on-line.

 

Mexican White Oak, another of my favorite trees, exhibits this yuzuri-ha characteristic also. Mine currently has old leaves, new young leaves and flowers all at the same time.

 


Mexican white oak (Monterrey Oak) showing Yuzuri-ha; old and new leaves together

 

Interesting stuff, but the most important point of all this is that no matter when the leaves come down, mulch then into the turf or on the driveway as the first step if you have no turf and use the excess ground up leaf residue to cover the bare soil in beds or turf areas. Into the compost pile as a last resort – never to the landfill.

 

 

 

 

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