Pruning Principles learned over a lifetime

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I have a lot of different kinds of plants to prune. Could you share some basic pruning principles that would apply to all kinds of plants?

Yes, there are some basic pruning principles I have learned over a lifetime which are applicable to all plants.

The most important principle I have learned from pruning thousands of plants is the type of pruning cut to make. It addresses the question: What do I want this plant to look like after it regrows following pruning?

There are 3 types of pruning cuts which each produce different plant growth responses. New growth after pruning is different, depending on the type of pruning cut.

Heading Above a Bud.  When a branch is shortened by pruning just above a bud, most plants respond by producing 3 or more shoots where one grew before. This response is based upon the principle of terminal dominance. The top bud sends auxin (a plant growth hormone) down the shoot which inhibits lower buds from growing. When this top shoot is removed, the inhibition is removed and several lower buds grow. Heading above a bud thickens the growth or makes it denser. Two specific examples are pinching and shearing. Whenever shears or power clippers are used, 95% of the cuts are above a bud. This results in 3 or more times as many shoots. After two shearings we multiply 3X3 and get 9 times as many shoots. Three shearings result in 27 or more times as many shoots. This is the kind of dense growth we want in hedges, so we normally shear them. That is why shearing should be avoided if we want to retain the natural thickness of the plant.

Heading Above a Side Branch.  When a branch is shortened just above a side branch, the growing tip in that side branch becomes dominant and sends an auxin signal down the branch inhibiting the development of lower shoots. As a result we get a 1 for 1 response. The plant grows one new branch where one was removed, resulting in the same thickness or density of growth as before. If we want resulting re-growth to be the same as before pruning, this is the primary kind of cut we should make.

Thinning or Removing an Entire Shoot or Branch. When shoots are removed entirely, the plant has less than one resulting shoot for each one that is pruned. Thinning makes a plant more open or less dense. This is the type of cut used to open up a plant which has become too dense. It is used to restore sheared plants to their normal thickness. Most pruning cuts on established fruit trees are thinning cuts because we want the maximum light to reach the fruiting branches, especially the lower branches which are easier to pick. This principle applies when less than 20% of the branch surface is removed. When more than 20% of the branches are removed latent bud growth is stimulated and one or more shoots can grow from the point where the branch was removed.