Minnesota Gardening Podcast
We bring together Upper Midwest gardening enthusiasts who are transitioning to a more sustainable lifestyle to explore eco-friendly landscape and gardening practices, so that we can reduce our chemical use, water use, and create a thriving ecosystem.
Minnesota Gardening Podcast
How Trees Know When to Turn: The Science of Fall Color đđđ
The leaves donât wait for frostâtheyâre already counting the night. We dive into the quiet timing system inside trees that decides when the colors ignite, why some years burst into crimson while others fizzle to brown, and how weather and latitude shape the show right above our heads. Itâs a guided tour of photoperiodism, phytochromes, and the pigments that paint fallâcarotenoids hiding under summerâs green and anthocyanins that arrive late to set maples and oaks on fire.
We break down how plants measure darkness rather than just daylight, why the red vs. farâred balance matters, and what âcool nights, sunny daysâ really does to sugars in leaves. Then we follow the story to its elegant conclusion: the abscission zone, a microscopic tear line that lets a tree reclaim nutrients and drop each leaf cleanly. Along the way, we connect the science to practical gardeningâhow healthy soil, reduced chemical use, and smart fall cleanup can protect pollinators, save water, and set up stronger color displays next year.
This is a nerdy, satisfying look at the biology behind peak color season, told through the lens of our Minnesota landscapes and the broader mission to build resilient, pesticide-free yards. If youâve ever wondered how trees âknowâ when to turn, or why reds pop only in certain years, youâll come away with answers and a toolkit of simple, high-impact steps you can put to work at home. Subscribe, share with a friend who chases leaf-peeping weekends, and leave a review to help more neighbors find the showâand consider joining our community to grow healthier landscapes together.
Join Minnesota Gardening as a member today for just $77 a season (this promotion ends today!)
Hello and welcome my friend to the Minnesota Gardening Podcast. My name is Brad Tadkey, and I am the host of the podcast, and I am honored to have you here with us today, where we are working together as Minnesota gardeners to grow a community of Minnesota homeowners switching to healthy landscape practices so that we can stop the exponential rise in pesticide-induced cancers, reverse the collapse of pollinator and songbird populations, and save our clean water. We are working really hard together to get that done. And it's no small task, obviously, and we are in the middle of our October membership drive. And today is the final day of our first time of offering quarterly memberships. And so we finished up our drive last week with annual memberships for our cheapest price that we have all year long. And uh today ends the weekend-long push for quarterly memberships. And a quarterly membership is every three months, and uh it is$77 to join Minnesota Gardening. And we work at Minnesota Gardening to help to get to healthy landscapes. And so if you are using chemicals, if you're using water, if you're not feeding pollinators and songbirds, and using your home landscape as a mechanism to make the world a better place, we're here for you if you want to make those changes and start to change from a uh uh toxic landscape to a detoxing landscape to a nourishing landscape to a healthy, thriving landscape where we have eliminated chemicals, feed pollinators and songbirds, saving water and storing carbon at our homes. So that's what we do. Just little things here at Minnesota Gardening. And this is a very personal uh crusade for me. I really want to make sure that we are doing the right things and our home landscapes for our kids, for our grandkids, for the future of our environment and everyone else involved. So I hope you join Minnesota Gardening. Uh, today is the final day of joining at our quarterly price of$77 per quarter. So I hope you join there. Today we are in a solo podcast episode and we are taking a deep dive into fall colors. And so this is kind of a nerdy, wonky episode for you. Um, oh, I just realized if you want to join, head to MinnesotaGardening.com. That is where I you're just listening. You're not uh able to see what I see here. And uh, if you would like to join as a Minnesota gardening member, head to MinnesotaGardening.com. All the information is right there, uh, and you can head in that way. So MinnesotaGardening.com. Now, today we are talking about fall colors. And so I get often questions about how this happens, like what the hell, right? Like, how how do trees and plants know that it is fall and they don't just wait for it to freeze and then fall off? They actually have a process that we all see and we all know um that is a changing of the seasons in our landscape plants, and that's the fall color change. And so that is the brilliant, you know, yellows and reds and purples that we see. How do those plants know before it gets cold how to change and when to change? And so it's a a process that we're gonna walk through today called photoperiodism, and so uh it's the plant's internal clock that it knows how uh long the days and how long the nights are, and once it hits a trigger point, and all plants are slightly different for that trigger point, um, then they start the process of shutting down for the winter. And so to me, this is along with like we've talked this month all about soils as uh Minnesota Garden members, and it is just fascinating to me how plants know and do these things. Do they think? Do they have a brain? Do they know? Uh do they have memory? What does do all those things even mean? And uh, so it is really, really fascinating to me that plants are able to do these kinds of things. And we don't really know, like we know the mechanisms, but we don't know exactly how they put it all together and get to uh the end product that we see as the just uh glowing sugar maples that we see in our parks and in our landscapes that are just glowing yellow, the uh brilliant, bright red uh oak trees. We don't know why they turn brilliant bright red and what the what the point of that is, and we'll get to that in just a little bit. Um, but we'll start with the plant's internal clock, and it's uh a thing called photoperiodism. And uh photoperiodism happens uh because plants are able to recognize and sense light, and so we intuitively know this because plants will uh you know grow toward the light, they will grow to maximize their leaf space that is exposed to the light, so for photosynthesis. Um but we don't actually uh often think about plants as seeing, and I'm using air quotes here, seeing the light, but they absolutely can. They have photoreceptors um called phytochromes that are in their stems, and those phytochromes are able to sense light. And so they're able to sense light um in the shutting down period in the fall, they're able to sense light as to timing as to when to start up in the spring. So when we get a uh a warm period that the plant doesn't just start growing because it's warm out, the plant starts growing because they're actually seeing how much light there is. And recently there was an interesting um, at least what I find is interesting, a really interesting uh research uh done about what actually the plants see. And what they see is not necessarily the daylight, but they see the lack of daylight. And so they have two types of receptors in their phytochromes. And those uh phytochromes, they measure the length of the nighttime. So what uh in the fall, when leaves are starting to shut down, what they've actually seen is that the nighttime gets longer, and that changes with location, right? So it changes at a different time, whether you're in uh Canada, whether you're in Minnesota, whether you're in Iowa, whether you're in Florida, those are all differences in uh nighttime length, and so the trees see that happening, and then they start to uh change based on that. And so there are two types of uh pigments that those plants uh have, and those are uh um phyto sorry, I was got lost in my my head there. Um, those are phytochromes that uh see far red light and see red light. And so the red light is active during the daytime, and uh the far red light is active during the nighttime, and so they have a chemical that breaks down through that time, and the amount that chemical breaks down through the nighttime periods is what the plant measures and knows when it has turned into autumn, when uh that uh far red level has dropped below a critical threshold, it triggers the start of dormancy and leaf change, and so that it differs from everywhere in the country based on your latitude and your location. And so it's just really, really interesting to me how this all happens. And so that's what triggers the change for the plants to realize that fall is happening and that they need to start that uh dormancy process for the season. And what happens next is even more interesting, I think. So there are a couple different ways that uh we'll focus mostly on trees here, that trees handle this, and so what happens is the uh uh daytime length is what triggers the process starting, but then as we see some years we see bright uh brilliant, bright uh colors, and other years we see pretty dull brown colors and those kinds of things. Uh, the weather and how fast the um the photosynthetic materials break down in those plants is what causes the different um uh amounts of light and so of colors that we see each year. And so if it is uh cool nights and uh warm sunny days, we get the brightest possible colors in our um fall colors. If it is really, really hot, like we had this year in 2025, uh, those fall colors will be uh drowned out a little bit because they are not getting what they need in order to break down uh well. The process happened way too fast. And so inside the leaves is really, really fascinating. So uh we all learned, probably I'm guessing, in uh middle school and high school in science that uh the leaves are generally, and there's two different types here, uh the actual color of the leaves are what you see in the fall colors, and those fall colors are just masked by chlorophyll. And so chlorophyll is the process for photosynthesis, um, the location where photosynthesis happens, and in those leaves. And so what happens is the plant creates chlorophyll, that chlorophyll masks the color of the leaf, and so that is the carotenoids, and so um the carotenoids are yellows and oranges, and those are what we see um in the fall, and but it's there all summer long, but we just don't see it because it's uh covered up by the chlorophyll, and um what they've learned recently as well is that when we have oak trees and uh maples that are deep reds and purples, those are the anthocyanins that are showing up at that point, but anthocyanins aren't present all year long. Those anthocyanins only come in once this trigger process starts. So we've got like uh a maple that is uh we'll say a yellow uh that has carotenoids in there, but then once the uh once it wants to turn red, it builds these, it grows these anthocyanins, which show up as reds and purples. And those are more, much more impactful when we have cool nights and a lot of sugars that are trapped in those leaves. And no one knows exactly why this happens and why they do them, um, but that is there, and so we've got those reds and purples, which are newly created colors in that leaf just for fall, and um again, fascinating process. Why trees do this exactly, we don't really know. Um, but it is there, and then uh the more interest I keep saying interesting. I should probably stop using that word, but I uh I do really think it's cool that uh plants also have what's called an abscission zone. And so that absission zone is that point where the leaf meets the stem tissue, so the the branch, the twig, whatever it is that that leaf is connected to, they uh they have to have a spot where the leaf separates from that twig. And so there's a uh a very clear layer called the abscession zone, where those cells, they just simply because of the fall process and uh what was triggered by this nighttime length of uh and day length and those photoreceptors, the have a layer of plants that of cells that just dissolve and uh they just uh self-destruct and they go away. And uh that is how a leaf falls off, is that those cells in the abscession zone just uh poof are done, and uh that's how the leaf falls off and it's ready for the next season to uh start growing again at some time. And when those phytochromes see that the day length is uh that the night length is shortening again, that's when the process starts back up again for starting to grow leaves and to do all that work uh in reverse of shutting down for the fall. So I'd love to know uh if you like this nerdy, uh wonky side of things. We're gonna do this on the podcast a couple different times here, uh, but I just really am uh happy to have you here with us today. Go back through a little bit here, and so photoperiodism is the kicker for what causes fall changes to start happening in our plant friends. And so they have phytochromes that are measuring the far red light spectrum, and that uh they are measuring how long the night is. And for that plant, once it hits uh a length of night that is growing uh to a certain amount, and every plant is a little bit different, triggers the fall process to happen, and those uh chlorophylls break down and then they move on to their fall color that is uh uh impacted greatly by weather and how much rain we have had. And then those leaves uh have a little chunk that uh dissolves and they fall off, and then we enter the winter season. And so, with that, I just appreciate you being here. I appreciate you listening and learning about healthy landscapes, and also encourage you on our last day of the uh quarterly um Minnesota Gardening membership uh push for October. I just really hope you join. It's 77 bucks a quarter and it's uh$77 per season and would love to have you as a member of Minnesota Gardening so we can save thousands and thousands of gallons of fresh, clean water. We can reduce the use of thousands of gallons of herbicide in our landscapes, we can feed literally millions of uh pollinators and songbirds with our landscapes, and we have to do that together. And with a hundred new members here in the month of October, we will do that. And so please head to Minnesota GardeningGut.com and join as a member. And I will see you in there very soon. Thanks a lot and have a great day.