I have always been of the opinion that the colder temperatures of late autumn are the main reason for good fall colour. Vertrees suggests that a reduction in moisture or slight stress may also help achieve better colouration at that time of year I have only just read in another forum This proposition has come as a complete surprise to me, and is contrary to anything I have read up until now, and probably even my own experiences Has anyone here any views and information on the subject?
Might be a plausible theory if there were actually "sugars in the soil". There are all sorts of nutrients in the soil that the tree requires, but sugars and carbohydrates are produced in the leaves (and other green bits) by photosynthesis. Stressed trees, in my experience, do not show the same intensity or vibrancy in colour that a non-stressed tree will. A tree stressed by drought or by excessively wet conditions will change and drop leaves earlier than a non-stressed tree but the colour doesn't last as long & advances through the tree (rather than changing all at once). Dry summer and falls seems to result in lots of yellows and browns. Best colour I see is in trees growing on ideal soils with optimal moisture for that species. Thats when the reds, oranges, etc. are at their best. Good fall colour is also influenced by fall temperatures. A good stretch of warm days and cool nights (above freezing though) will trigger the best colours & synchronize many different species. The trees need the cold nights to trigger leaf drop but they also need the warm days to 'metobilize' the chlorophyll to reveal the vibrant colours. Universally too warm?....leaf drop is not triggered before frost kills the leaves. Universally too cold?....leaf drop is triggered but the temperature is too low to metobilize the chlorophyll & very little colour change occurs before frost kills the leaves. Simon
Climate plays a large part, as colours are better in regions with continental climates, but genetics is also important - species which colour well in continental climates (e.g. Acer rubrum) also colour better in oceanic climates than the local oceanic-adapted species do (e.g. Acer pseudoplatanus) even when they are planted in oceanic climate areas. I've an idea that the likes of Acer pseudoplatanus also don't colour as well even if planted in areas where the local natives do colour well (though colouring better than it does here). So the question is more complex than just the climate.
It is certainly complex. There is the problem of the same species having variable colour intensities according to geographical location; then there is the tree planted in a given place with colour intensities that change from year to year depending on the climatic pattern that given year. Less common is total colour change, in my garden a large acer palmatum that has always had a beautiful golden yellow, turned orange this year for the first time. I've tried to figure out why but I have not found any convincing explanation. Gomero
Doesn't New England have exactly the kind of 'cold' weather at the right time of year that has always been attributed to good autumn colouration? Yes Gomero ... I too have noticed the different colours I get on the same plant in different years To me that is part of the fascination of these wonderful plants
This year in the PNW the colors of the japanese maples were very unusual. i noticed it early this year on several of the red varieties which came out red and quickly changed to green and stayed green all summer. Acer palmatum 'Red Pygmy' was one of them and I spoke with several people in Oregon and they all experinced the same with the tree. I also have seen some of my favorite fall trees be a bit of a dude like Ap 'Iijima sunago' which turned a dull yellow. I am really suprised at how much weather can change the trees. I do not beloieve next year will be any different since I have new growth on treess which have turned the fall color and dropped their leaves.
This year in the NE is has been very wet, warmer, but with cool nights. The colors on my maples have generally been very good, but leaf drop quick and very staged with species, with Palmatum generally doing better than Japonicum or in my microclimate. I did get a true intense orange to red in S. Ogurayama this year for the first time and the leaves have remained better than most, too. I have bare trees and green right next to each other, somewhat differently from other years here. I'm still waiting for the Shishigashira show. The general fall colors have been good, too. I've seen some stunning red maples, and my native stewartia were intensely colored.
check out the article on the reasons for autumn color on the US Arboretum homepage: www.usna.usda.gov enjoy!
I noticed the colors were much more intense this autumn. And our temps have been cool, but to very cool. Our summer weather seemed a bit different too. Knowing that a good portion of autumn leaf colors have already been in the leaves in summer and are revealed in autumn, I'd suspect that the summer growing conditions can have a lot to do with autumn color, as well. The arboretum article was pretty good.
I was looking through last years photos in search for a photo of an AS 'Garden Glory' I did not find a photo of the tree but what I did see was last years japanese maple tree colors in my yard were much more intense last year than this year. Some of the trees this year may have became the same colors but in many cases it was not on the whole tree like the previous year and in many cases this year trees turned a wonderful color only to loose their leaves to the wind and rain in just a couple days time.
