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Gardening Answers Knowledgebase

Plant Answer Line Question

Keywords: Leaf marcescence, Leaf abscission, Hamamelis

I'm wondering if there is a way to get the leaves to drop off of my witch hazel in the fall, or before it blooms?


Some witch hazels have a habit of holding onto their dead leaves (this is called marcescence). Leaf drop (leaf abscission) can also be affected by weather patterns or by the age of the tree. The only way to get them off the tree before they finally do it themselves is to remove them by hand.

An article by Phil Clayton, published in the January 2007 issue of The Garden, mentions that some yellow-flowered varieties have this trait. Here is an excerpt which quotes Hamamelis expert Chris Lane:
A (...) free-flowering yellow selection (...) is H. x intermedia 'Ripe Corn'. The only downside is its habit of hanging onto old leaves as the flowers open. This trait occurs in some other cultivars and is usually frowned upon by growers (...) a mild autumn followed by a sudden frost can make more leaves hang on to branches. Fortunately, as with H. x intermedia 'Ripe Corn', older plants often grow out of the habit.

An article entitled "Ranking the Scents and Sights of Hamamelis" from the February 25, 2011 posting in Swarthmore College's Scott Arboretum Garden Seeds blog also includes a chart "Ranking Leaf Retention and Fragrance of Hamamelis."

Date 2017-05-06
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Plant Answer Line Question

Keywords: Leaf abscission, Vitis

Why do grape leaves fall off the vine in fall to early winter? What happens physiologically? What triggers dormancy?


The book Oregon Viticulture (Oregon State University, 2003) describes dormancy, acclimation, and cold hardiness:
"In autumn, the vine enters dormancy--the stage with no leaves or growth activity, which extends until budburst the following spring. Despite the apparent inactivity of this stage, it can be a critical time for grapevines when they may be exposed to potentially damaging low temperatures [...] There are three stages of the dormant season: acclimation, the period of transition from the non-hardy to the fully hardy condition; midwinter, the period of most severe cold and greatest cold hardiness; and deacclimation, the period of transition from fully hardy to the non-hardy condition and active growth."

This book does not address leaf drop (abscission) nor does it explain the physiological reasons a vine enters dormancy. The Grape Grower by Lon Rombough (Chelsea Green, 2002) says only that leaf drop follows harvest time, and is part of the vine's hardening off process: "The leaves drop, the shoots become woody to the tips, and the vine gets ready for winter. This is when the vine undergoes deactivation and reenters dormancy." To find the scientific explanation you are seeking, it might make sense to contact a plant physiologist who specializes in vines. There are specialists at University of California, Davis's department of Viticulture and Enology.

I consulted Plant Physiology (4th ed.) by Taiz and Zeiger (Sinauer Associates, 2006), and here is what it says about leaf abscission in general:
"These parts [leaves, flowers, fruits] abscise in a region called the abscission zone, which is located near the base of the petiole of leaves. In most plants, leaf abscission is preceded by the differentiation of a distinct layer of cells, the abscission layer, within the abscission zone. During leaf senescence, the walls of the cells in the abscission layer are digested, which causes them to become soft and weak. The leaf eventually breaks off at the abscission layer as a result of stress on the weakened cell walls.
Auxin [plant growth hormone] levels are high in young leaves, progressively decrease in maturing leaves, and are relatively low in senescing leaves when the abscission process begins."

Here is a little information about vine dormancy, from U.C. Davis.
"In late autumn, triggered by short days, petioles detach from the shoot and leaf drop occurs. The vines can no longer manufacture carbohydrates through the process of photosynthesis and are storing carbohydrates in the form of starch. This dormant state will continue until daylight hours and temperatures increase in spring, when axial buds that were formed before dormancy become activated to break."

Date 2017-07-18
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Plant Answer Line Question

Keywords: Leaf marcescence, Leaf abscission, Quercus, Fall foliage

I have a large lawn with a southern exposure, and fairly good drainage. I would like to plant 1-3 large shade trees. I have been considering northern red oaks for the location, as they seem to grow well in this climate, should provide good shade, and they have nice fall color. However, I don't like oaks which keep their dead leaves through the winter (as Scarlet oaks do). I find the dead leaves unsightly and messy, and I will not want the shade in the winter. Do red oaks also keep their dead leaves on their branches in this manner? If so, have you another recommendation, other than maples?


According to the Sunset Western Garden Book, pin oak (Quercus palustris) keeps its brown leaves through the winter, but Northern red oak (Quercus rubra) loses them in fall. The retention of leaves in fall (meaning that they delay dropping them until spring) is a phenomenon called marcescence. At times young trees of other oak species, even Quercus rubra, can keep their leaves all winter, particularly if it is an unusual winter. You might consider Katsura tree (Cercidiphyllum japonicum) or sweet gum (Liquidambar styraciflua) for fall color with more reliable leaf drop.

Date 2016-12-22
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August 01 2017 12:36:01