Tree vigor

  • February 3, 2023 at 4:10 pm #17161
    Andy King

    I have a couple of very vigorous apple trees that are almost twice the size of most of my others. One is a Northern Spy (which I posted about in the Varieties section). What can a grower do to get them to settle down? I assume that there are special ways of pruning strong growers like this.

    February 3, 2023 at 5:06 pm #17165
    Todd Parlo

    This answer you can accept as general information related to all fruit trees, not just apples. Vigor is programmed- genetics pure and simple, so some of it we need to plan for, and some of it we can mitigate. There are exceptions, but often the more powerfully growing cultivars are only going to show fruit after making you wait. The two are inversely related in many cases. What is happening here is the tree allocating resources- and with this particular genetic trait it wants to make a big tree first. Fruitfulness is set aside when trees are growing this strong- in general. There is another factor here too, that of branch orientation. In many strong growing trees there can be a higher percentage of vertical growth. Vertical shoots are the strongest in terms of outright vigor. Spy is a case in point, so is Sweet Sixteen (which has Spy in its lineage). This branch orientation phenomenon is a place you may have influence. Bend them down with whatever means at your disposal and the vigor will be reduced on those shoots. Don’t overdo it, just get them toward that 45-60 degree mark instead of straight up to the heavens. This is a common practice to slow up growth and incite fruit bud formation regardless of the tree variety. Pruning, despite being tempting is usually the wrong move. Especially when done when you are normally wise to (dormant season)… you will make matters worse by having a rebound in rank growth. All things considered the tree wants to go through this childhood phase by pushing, then it will settle and produce fruit so you have to move slowly in altering the tendency as well. Get the branches widened a bit to the horizontal. Also be careful with fertilizing as excess will only increase vigor, and delay fruiting. Do enough to keep the tree healthy and no more. Summer pruning can help but I usually coach against it unless you really know what you are doing, as it can be risky. What you can expect (this being the bright side) is the tree behaving once crops appear. The resource competition of developing fruit is one of the most powerful mechanisms for vigor reduction.

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