Tracy DiSabato-Aust (Garden Designer and Author) gives expert video advice on: What is 'pruning'?; What variables are involved in pruning?; How much pruning does a plant need? and more...
What is 'pruning'?
Pruning is not normally associated with herbaceous plants, as we often think of woody plants that we're shearing or shaping them. A U-shrub, for example, or a boxwood. But really, we do a lot of pruning with herbaceous plants. And when we pinch a plant, when we cut it back before or after flowering, when we deadhead or dead-leaf, those are all pruning techniques.
What variables are involved in pruning?
What to prune, when to prune and how to prune will vary from region to region. It will vary with the age of the plant, annual weather conditions, the soil fertility or moisture level, and just simply the gardener's objectives. Some years you might want a little neater look to a garden, another year you might want a delayed flowering for a special event, or to time it with an open garden tour, so it will just vary with your garden objectives.
How much pruning does a plant need?
That would depend on the type of plant, on the species and again what your objective is. Some plants, like certain Geranium, really require pruning after flowering to keep them looking good. With many of our spring flowering plants, a lot of people grow the moss phlox and that really should be sheared after flowering to keep it nice and full. So, again, it's very species specific on what we prune and when we prune.
Which plants don't respond to pruning before they flower?
Any plants that have a single stem, like cracosmias, delphinium, some of the foxgloves, don't respond as well to this pre-emptive pruning before flowering in an effort to delay bloom. This is because they have that single flowering stem that's unbranched. And so if we prune, we're basically removing that flowering stem.
What is 'deadheading'?
Deadheading is removing spent or dead flowers in an effort to prolong bloom or to cause a repeat later in the season of bloom.
What does it mean to 'cut back' a plant?
We cut back a plant either before flowering, to reduce the need for staking or to delay flowering, or we cut back after flowering to keep a plant nice and full to reduce that hole that sometimes will develop in the centre of many herbaceous perennials.
Why would I want to delay my plants from blooming?
This is really a fun technique. I tell people this is when we go beyond the "mow, blow, and go", where it's just the simple deadheading, or just simply cutting back after flowering. We want to delay flowering, especially if we're into flower arranging. We can have flowers much later into the season. We can also delay flowering for a special event. Maybe you're having a wedding in the garden, or you're opening your garden for tours and you want the plants to flower later, we would delay them. One other reason too is there might be something not quite right in the design combination. And you don't like the colors that are being used at the same time. If you delay flowering on one plant, you won't have that jarring combination at the same time.