JonW
Shohin
It seems like some people look at fall or winter as the best time to prune deciduous trees while the leaves are off, while others wait until summer after the first flush of leaves harden. What do you do and why?
I tended to be a winter pruner because I could see what I was doing and I have the spare time to work on (and enjoy) my trees. In the spring you get two benefits: the tree only puts its energy into the buds you left behind (or in other words, selected as places you want branching the following year), and you get back-budding and ramification.
Brent Walston's articles on Evergreen Gardenworks elaborates on this - and maybe I'm missing it, but I don't think he gives a simple answer, but rather lays out the effects winter pruning would have:
"The strongest response to terminal bud removal will occur in winter because there will be no bud break (and subsequent suppression) until soil temperatures begin to warm up and the roots begin to grow, signaling the buds to break into leaves. Thus winter pruning will produce the most bud break by interrupting apical dominance (terminal bud suppression) for the longest period. Summer pinching of the terminal bud will ordinarily give you only a two bud break, resulting in good ramification. So winter is the time for most heaving pruning, spring is the time for ramification pruning."
"Leaves manufacture plant food, roots store plant food.
OK, obvious again, but what are the ramifications? Top pruning a plant at the end of the season (fall or winter) leaves all of the food intact to stimulate new growth in the spring. A full complement of food with no where to go will stimulate new buds and the new growth will be explosive and coarse, some deciduous plants may send out an eight foot sprout one inch thick in a single season (or more!). Severely top pruning a plant just after it leafs out in the spring uses up most of the stored food because the roots must send out a second burst of food to stimulate even more buds. This depletion will cause very weak new growth and will slow the plant down.
Not pruning a plant in winter or spring leaves the maximum number of buds to be stimulated into flowers and leaves and twigs, this taxes the roots to the fullest and will produce the smallest leaves, and the closest internodes (spaces between the leaves) on the new stems. Confining roots, as in a bonsai pot, limits their ability to store food, which in turn will diminish the leaves and internodes even further. This is the basic mechanism for dwarfing a plant in bonsai."
I'd highlight a few bits of info:
Lastly, Brent also discusses the role roots play in food storage during winter:
"Removing root storage in winter will have the opposite effect. LESS food will find its way into a full complement of buds, causing shorter internode length and smaller leaves. This is what happens in dormant root pruning and repotting. Removing roots during the growing season doesn't significantly upset the food balance, but it does upset the water uptake/ transpiration balance and thus must be accompanied by top pruning, foliage reduction, or environmental change to keep from stressing the plant."
"Confining roots, as in a bonsai pot, limits their ability to store food, which in turn will diminish the leaves and internodes even further. This is the basic mechanism for dwarfing a plant in bonsai."
Removing roots removes energy for spring, which should hypothetically result in finer growth during the spring. If you had to do significant winter pruning to the top of the tree, you could balance this with root pruning so there is less energy divided over fewer buds, avoiding a burst of coarse growth in the spring. Correct? However, he also mentions that confined roots also confine top-growth in the spring. I've found that sometimes root pruning slows growth (especially if your moving to a smaller pot), but some species grow roots so quickly that anytime they are repotted, including if they are heavily root pruned, they have coarser growth in the spring - I'm thinking particularly about my Ficus Carica (common fig). I can basically hack it back to a cutting, and it will burst with energy, but the internodes shorten when the roots are a bit more confined.
I tended to be a winter pruner because I could see what I was doing and I have the spare time to work on (and enjoy) my trees. In the spring you get two benefits: the tree only puts its energy into the buds you left behind (or in other words, selected as places you want branching the following year), and you get back-budding and ramification.
Brent Walston's articles on Evergreen Gardenworks elaborates on this - and maybe I'm missing it, but I don't think he gives a simple answer, but rather lays out the effects winter pruning would have:
"The strongest response to terminal bud removal will occur in winter because there will be no bud break (and subsequent suppression) until soil temperatures begin to warm up and the roots begin to grow, signaling the buds to break into leaves. Thus winter pruning will produce the most bud break by interrupting apical dominance (terminal bud suppression) for the longest period. Summer pinching of the terminal bud will ordinarily give you only a two bud break, resulting in good ramification. So winter is the time for most heaving pruning, spring is the time for ramification pruning."
"Leaves manufacture plant food, roots store plant food.
OK, obvious again, but what are the ramifications? Top pruning a plant at the end of the season (fall or winter) leaves all of the food intact to stimulate new growth in the spring. A full complement of food with no where to go will stimulate new buds and the new growth will be explosive and coarse, some deciduous plants may send out an eight foot sprout one inch thick in a single season (or more!). Severely top pruning a plant just after it leafs out in the spring uses up most of the stored food because the roots must send out a second burst of food to stimulate even more buds. This depletion will cause very weak new growth and will slow the plant down.
Not pruning a plant in winter or spring leaves the maximum number of buds to be stimulated into flowers and leaves and twigs, this taxes the roots to the fullest and will produce the smallest leaves, and the closest internodes (spaces between the leaves) on the new stems. Confining roots, as in a bonsai pot, limits their ability to store food, which in turn will diminish the leaves and internodes even further. This is the basic mechanism for dwarfing a plant in bonsai."
I'd highlight a few bits of info:
- Energy stored for the winter is divided across all the buds on the tree in spring: the more buds, the finer the branching and shorter the internodes. The fewer buds, the coarser the branching and longer the internodes. Especially for a tree in refinement, we'd want to avoid excessive winter pruning in order to achieve and maintain fine growth.
- Removing the terminal / apical bud in winter removes suppression of lateral branching for the longest period of time, resulting in the most back-budding and lateral branching / ramification in spring (while summer removal of the terminal/apical bud only results in a couple adventitious buds breaking).
- Winter is the time for heavy pruning: this statement seems counter to the first statement. Many people suggest structural pruning in winter while you can see the tree well (without leaves), but others warn of opening wounds that can become infected while the tree isn't growing and cannot close/heal the wounds. This heavy winter pruning for structure would hypothetically be done on a tree in development (or a tree that was refined but got overgrown). Then you'd have to deal with the coarse growth / long internodes in the summer - as Brent mentions, you can in turn cut this growth back hard (early in the season) and get a second, weaker flush.
Lastly, Brent also discusses the role roots play in food storage during winter:
"Removing root storage in winter will have the opposite effect. LESS food will find its way into a full complement of buds, causing shorter internode length and smaller leaves. This is what happens in dormant root pruning and repotting. Removing roots during the growing season doesn't significantly upset the food balance, but it does upset the water uptake/ transpiration balance and thus must be accompanied by top pruning, foliage reduction, or environmental change to keep from stressing the plant."
"Confining roots, as in a bonsai pot, limits their ability to store food, which in turn will diminish the leaves and internodes even further. This is the basic mechanism for dwarfing a plant in bonsai."
Removing roots removes energy for spring, which should hypothetically result in finer growth during the spring. If you had to do significant winter pruning to the top of the tree, you could balance this with root pruning so there is less energy divided over fewer buds, avoiding a burst of coarse growth in the spring. Correct? However, he also mentions that confined roots also confine top-growth in the spring. I've found that sometimes root pruning slows growth (especially if your moving to a smaller pot), but some species grow roots so quickly that anytime they are repotted, including if they are heavily root pruned, they have coarser growth in the spring - I'm thinking particularly about my Ficus Carica (common fig). I can basically hack it back to a cutting, and it will burst with energy, but the internodes shorten when the roots are a bit more confined.
