Thinning as a practice

(Question)

Thinning is something that doesn’t correspond to our lifestyles, since people think more is better. In my mother’s garden of peonies, roses, phlox, hostas and mums, I’d like to thin the plants for various reasons. Is thinning subjective, or is there an optimum goal, like haircuts?
I see the advantages in this west-end garden, where I could then enjoy the gist of the garden’s beauty, and keep the maintenance minimal so I can see the weeds, problems without too much clutter, and with room to move around myself.
I wanted to try to clip 5% per week, thinking that by the end of 20 weeks, the plants will be pruned for fall. Is this feasible, or unrealistic? In the GTA, I’ll bet most of these perennials will be gone by then anyway.
Isn’t there an overlap between thinning & pruning?

(Answer)

Thank you for your question to Toronto Master Gardeners.

Thinning refers to the practice of removing smaller, weaker plants to make space for larger, healthier ones, usually in the vegetable garden.

Pruning refers to the practice of taking care of the limbs and branches of trees, shrubs and perennials by removing those that are dead, diseased, dying, leggy, thin or crossing over other branches.  There are numerous reasons to prune.  It sounds as if you would like to give your mother’s plants some more space for air circulation, which will help prevent disease and pests from settling in.  You also want to see the plants at their best.  Pruning them so they produce beautiful flowers in a pleasing form is a wonderful goal.

I would not recommend a 5% random cut.  Each shrub has its ideal for pruning and, actually, each has an ideal percentage of cutback per season.  If you are interested in learning more, two excellent guides to pruning all sorts of shrubs and trees are:

  • Pruning Made Easy: A gardener’s visual guide to when and how to prune everything, from flowers to trees  by Lewis Hill
  • The Pruner’s Bible: A Step-by-Step Guide to Pruning Every Plant in Your Garden by Steve Bradley