Sudden Ginkgo leaf fall

A number of people noticed this year that the leaves of ginkgo trees turned bright yellow, as usual, and then suddenly dropped all their leaves literally overnight leaving a golden carpet of leaves around the trees. This is actually pretty normal too, but usually it happens along with a lot of other trees dropping leaves, so fewer people notice.  2016 has been a long warmish fall with no good hard frosts before there was a very cold overnight freeze.  What happens is this. The shorter, cooler days stops the production of chlorophyll that ordinarily masks the yellow pigments (carotenoids, xanthophylls) and the leaves turn yellow. This is pretty common for lots of trees. At the base of the leaf stalk deciduous trees form a week place called an abscission zone, and in most trees a bit of back and forth bending in the wind causes the leaf to fall.  Gingko makes such a zone, but some of the vascular tissue remains connected and it takes a freeze, forming some ice crystals, to break the residual vascular connection, so after such a freeze, the leaves all fall at once. One day ginkgo trees have yellow leaves, the next day the trees are bare and the ground carpeted with ginkgo leaves. 

Golden rain and fall color

Fall color this year is varied and very good this year, but as always fleeting. The area immediately behind our house is under the canopy of two sugar maple trees, one large and one huge, and the light especially in the late afternoon is just perfused with a completely lovely golden glow. And as a bonus, the weather was warm enough to sit on the patio and enjoy the light with a glass of wine.  But then it started to rain, not water, not cats and dogs, not frogs, but leaves, and it

rained for 3 days burying the entire area with inches of golden orange maple leaves.  Several other species have contributed to the fall color too: yellow - bottle brush buckeyes, orange - sumac, red - dogwoods, pinky orange - black haw, red-orange - black gum, and variously peachy yellow, orange, and red - Japanese maples making bright dabs of color here and there in the gardens.  This one (Acer japonicum 'aconitifolium') is fairly new, but what a beauty, what color.

First it snowed, then it leafed

Our area got about an inch of snow last evening, the first of the winter, and not so unusual for November 12.  And then the temperature dropped to 19 F (-7 C) over night. Again nothing so unusual for this time of year.  But the fall has been lingering and late, so this is rather sudden cold and a hard freeze.  TPP decided that the gardening season was over and harvested the last of the bok choi and moved a couple of small boxes of parsley indoors.  Several of our trees really never did change color, and they were holding fast to their leaves.  Only the sugar maples had really dropped most of their leaves.  But this morning if leafed.  To explain, TPP's book editor is big on parallel construction, so "snowed" "leafed"; that's parallel right?  All those leaves that were hanging on literally dropped all at once.  It was leafing hard on the back half of the estate this morning and it was kind of magical and sort of pretty; if you had stood there with a basket it would have filled pretty quickly.  It was quite a sight except for all the leaves falling into the lily pond.  A sudden leaf drop usually this happens with ginkgo trees, but these other trees not so much.  Now there's a leaf-snow-leaf sandwich on the ground that's 3-5 inches thick.  Raking season has officially begun. 

Suddenly deciduous

Last night it froze; the low temperature was 25 F.  Up until now only the lightest of frosts had happended, so lots of trees still have green leaves.  Under these circumstances a number of tree species will drop their leaves all at once including hackberry and black walnut, and most definitely ginkgo.  What causes tree leaves to drop is an abcission layer, an anatomically weak zone that forms in the fall at the base of the leaf stalk.  Trees like ginkgo still hang on to their leaves until a freeze, and then, perhaps as a result of ice crystal formation, the weak connection is broken and as the temperature goes up a few degrees, all the leaves fall at once.  TPP sort of wishes other trees did the same because then you'd be done with it, but some of our big trees hang on to leaves so tenaciously you end up raking in the spring.  The areas under the suddenly deciduous trees were just a carpet of dropped leaves this morning, and most people won't even notice. And leaves were still falling like rain.  Most other trees drop leaves more gradually as the abcission zone matures.  All trees drop leaves, but when they drop them all seasonally, they are deciduous.  Otherwise they are evergreen, which is not synonymous with conifers because some are deciduous.