How can you determine how many times a year a tree can be partially defoliated? I have performed it once on my deciduous in refinement but am trying to determine when the next time can be done? The trees have shoots that have extended several pairs of leaves and have hardened off. But we are also in mid 90s everyday. Does that impact whether I can perform the next partial defoliation? Or should I wait until the end of summer for the next round?
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What kind of tree? I’ve done it for a second time on my crape myrtle. Considering a second round on my water jasmine. Only did it once so far on my pecan.
I’m kinda in the same boat on a few different species not sure if/when the next round. So I have a trident maple, Korean Hornbeam, winged elm and crepe myrtle. They had previously been in development so this is my first steps Into refinement with them so I’m a bit hesitant on application of these techniques.
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Have you let your trident maple run out several shoots? I normally go into a pinch out the center set of leaves as soon as I can see them after I partially defoliate. It will keep the first internode from lengthening as much and encourage the tree to keep pushing new shoots.
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Here are pics of some of the trees. We’ve also been in mid to upper 90s. Does that affect timing of pruning? For example, if these are ready for another pruning, is it still of to do in the heat?
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I would be tempted to wait until slightly cooler weather. When you reduce the amount of foliage it reduces the tree’s ability to transpire. If you did do it you would have to keep moving it into shade as the day heats up.
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As Ryan says; when in doubt we’re hands-off. You’re not going to hurt the tree by not doing something. That said, I don’t partially defoliate my elms. I follow the Dennis Vojtilla technique with those and cut back to one or two nodes after the shoot has elongated to 5-7 nodes.
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Do you know if winged elms are any different? They seem like a small leaf species as well so I think that’s the guidance to only post harden prune without cutting leaves. But I struggle with only getting a single strong shoot at each cut sight so I don’t ever get any bifurcation.
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I’m not familiar with winged elm, but those don’t look like what I would consider to be small leaves. In your next round (whenever you decide that should be) you can try cutting the leaves as well.
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Reducing leaf area will reduce water stress, so I see no problem with doing it now. As long as the trees aren’t getting nuked by the sun, warmer temps will result in faster growth. My deciduous have been going nuts this week with the warmer weather, I just did the second defoliation on my fastest growers.
I checked out my crape myrtle today. It’s already pushing new ramification after the second round of PD.
I agree that the majority of deciduous do go nuts when it warms up, but when it gets really hot they tend to slow down, if not stop. Partial defoliation opens up the interior, so unless shade can be given when it’s hot damage will occur. Especially to the interior leaves and new buds. Ryan did say that partial defoliation reduces the tree’s capacity to transpire, which is logical and something I’d never though about. Either way in the high nineties I think it would be best to be hands off. Just my personal opinion…
Understood. I think with shade and water it shouldn’t be an issue for many species, but others could certainly be harmed. I get that transpiration capacity could be reduced at the individual leaf level following partial defoliation, but at the canopy level the amount of transpirational demand will drop. I proactively reduce leaf area before a heat wave to save some of my sensitive deciduous, but I also live in a really low humidity area. I can see how this would be a very climate dependent balancing act.
I did a second round and a semi-late first round on my heat loving trees. I’m still debating doing a second round on my water jasmine. It’s a tropical, so it should be able to handle it.
This is definitely going to be a species to species discussion on top of a micro-climate to micro-climate discussion. That’s what makes it exciting and takes our game to the next level. Instead of being told “You handle X species Y way at Z time of the year” we’re being told “Hey, this is a tool in your tool belt. Time to put on your bonsai big boy/girl pants and figure out how to use it.” I tell my wife all of the time that what I’m really doing is running a series of experiments in the backyard. I just happen to be trying to make the trees look nice while I’m at it. 
I also (informatively) kill plants for a living in the name of science. I’m less good at knowing what makes them thrive, so maybe ignore everything I say 
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It’s funny but just when you think you’ve learned all there is about a tree species it will throw a curve ball and do the exact opposite. So even after 25 yrs I’m still learning - which means getting it wrong sometimes.
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Thank you everyone for all the input and answers! Its been a crazy week so I wasn’t able to respond to earlier. I really appreciate the guidance!
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