The goal of keeping trees small involves manipulating its growth patterns through pruning and potentially using plant growth regulators. This is a nuanced endeavour and there are both pros and cons to consider.

Pruning vs Growth Regulators

1. Pruning: This is the mechanical removal of branches and leaves to control size and shape. It is intensive but allows for precise control.
2. Growth Regulators: Application of growth regulators can help manage tree size but are less precise than pruning.

Choosing a Growth Regulator

The most commonly used growth regulator for reducing tree size is Paclobutrazol. It inhibits biosynthesis, leading to reduced elongation, which makes for a more compact tree.

How to Use Growth Regulator

1. Timing: The best time to apply is during the tree's dormant season or early in the growing season before new growth starts. This maximizes the uptake and effectiveness of the growth regulator.
2. Application Methods: The common methods are soil injection and trunk injection.
3. Dosage: This varies based on the size and age of the tree, but it is crucial to adhere strictly to the correct dosage.

Considerations

1. Longevity of Effect: One application of a growth regulator like Paclobutrazol can reduce growth rates for multiple years, so it's a commitment.
2. Other Physiological Changes: Reduced growth often comes with thicker leaves and intensified coloration, which may or may not be desirable.

It should be applied with precise timing and dosage, considering the tree's specific condition and the long-term management goals.