Why Leaves Change their Color

Things I love about fall:

  1. Apples
  2. Apple Cider
  3. Apple fritters

Oh, and the fall colors too.

Oh the fall colors! Bold oranges, deep maroons, brilliant yellows. Have you ever wondered why (or how) they happen? If you’re the romantic sort, you may think of this transition as “a second spring when every leaf is a flower.” If you’re more of the marmot-y type, you might see the changing leaves as a reminder that winter – and thus, hibernation time – is coming. Or, if you have a more macabre turn of mind, you see the leaves changing colors as a sign of death. Which I guess it is, because the leaf tissue is dying.

Swan Flat road, Logan Canyon, fall colors, autumn


But let’s focus on the hibernation part. Not just because I am somewhat marmot-y in nature and feel the need to hibernate when the days start to shorten, but because that’s essentially what the trees are doing. They’re going into hibernation mode.

During the spring and early summer, those green leaves are hard at work processing light energy into sugars needed for growth. Though there are many pigments in the leaves, the chlorophyll is the most abundant – and the main player in the photosynthetic process – so that’s why we see the leaves as green.

As the summer transitions to fall, the leaves start shutting down their sugar production and the tree to puts the sugars into storage for future use. Because the chlorophyll isn’t needed, it is no longer produced and the other pigments, anthocyanins (reds and purples) and carotenoids (yellows and oranges), start to become more visible.

fall colors, fall, autumn, aspens, changing leaves

Eventually the chlorophyll is depleted, the sugars are stored, and the leaf is no longer needed; so it falls off into wonderful (or dreadful, depending on your perspective) piles to rake up and jump into. Or to crunch through as you walk down the street. Or to just enjoy.

fall, autumn, changing leaves, falling leaves

There are a lot of environmental factors that influence the brilliancy of the changing colors, including: drought, too much precipitation, temperatures, general health of the tree. The best colors come on years where the water has come at the right times and in the right amounts and the temperatures during the day are warm while the temperatures at night are cool. A cold snap too early (as in really really cold), not enough water during the spring/summer months, or not cool enough temperatures at night generally result in less-than-stellar leaf color. I think around here it’s been a combination of these things. Some of the aspens have looked really great, but the maples are a bit lackluster. Fall of 2012, on the other hand was outstanding. I was looking through my fall foliage photos and almost all of my favorites came from that year. The fall fates were very kind that year.

red leaves, maples, fall colors, fall, autumn


  1. So cool – I’m pretty sure I learned all of that once upon a time, but I love your simple and easy to understand explanation.

    • Heather

      October 8, 2015 at 7:22 am

      Thanks! I think it’s a fascinating process – but I am an admitted nerd – so I’m glad someone else enjoyed it too!

  2. I have lived in New England my whole life and the fall foliage never ceases to amaze me! I went for a walk this morning and felt myself stopping to admire all the deep red and oranges. How amazing is nature!? Beautiful pictures… and thanks for the explanation!

    • Heather

      October 12, 2015 at 8:03 pm

      I think fall must always be lovely in New England if for no other reason than the sheer quantity of trees. I’m glad you can enjoy the colors!

  3. Petter Granberg tror jag mkt på. Han visade upp en del positiva tenednser redan ifjol. Duktig back som kanske kan ta för sig en hel del till vintern.

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