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Friday, April 1, 2011

Rose of Sharon : How To Prune, When To Prune

Pruning Rose of Sharon [Hibiscus syriacus] Pictures, Video

Brueckner Rhododendron Garden Head Gardener demonstrates how to prune Rose of Sharon, a late summer blooming shrub in the hardy hibiscus family, and offers these How-to tips:
  • When to Prune: Now; early spring in Mississauga, Ontario
  • How to Prune: Open method, not closed
  • How much / how many canes (branches) to prune
  • How to control or maintain shrub height
  • When to fertilize: After Pruning, and regularly all season
Here are some pictures with more detail, and a video showing how these Rose of Sharon bushes were pruned, using the Open Prune method, not the Closed Pruning method.

Rose of Sharon shrub before pruning ~ Head Gardener BRG Mississauga
 As you might infer from the warm-looking jacket and heavy gloves worn by the gardener, it's still chilly and wet in early Spring in Mississauga. Snow flurries still threaten, but generally the plants are thinking ahead to the coming summer blooming season.

This is the time to prune Rose of Sharon, and other summer flowering shrubs.

Tip: This is also the time to prune roses, so think Rose of Sharon = roses. (See Pruning Roses on this page.)

This long-unpruned Rose of Sharon was transplanted to its new home in BRG last summer,  a mass of tangled and crossed branches. But, having survived the winter, it's now time to give it a good pruning, with a goal to open up the crowded interior of the plant to let air and sunlight in. This is the Open method; the Closed method is trimming off all branches on the outside of the plant, more suited to hedge plants and topiary.

Rose of Sharon ~ Count the Canes Before Pruning
 The rule of thumb for pruning any shrub or tree is to remove no more than one third of the growth; Leave the plant with sufficient resources to nourish itself. Dead canes are already compromising the health of the shrub, so are included by default into the total canes to be pruned.

And to determine how many branches you may safely remove (prune), you must first count what is there, including any damaged or dead canes.

In the shrub above, there are 9 main canes (branches) coming from the ground, so three canes including dead and damaged canes could be removed.

Pruned Canes (Branches) Rose of Sharon
 Using clean, sharp pruning shears or cutters, trim canes selected for removal. Note the angle of the cut: aim for a slant of about 45 degrees. This angled cut will make water run off the pruned cane; a Flat, straight across cut will create a bowl that collects water, and tend to pool water and encourage rot and fungus.

First decide which, if any, of the main canes to prune. Give priority to canes that have visible damage in the bark, or have been broken over the winter, or canes that are crossing or rubbing against their neighbours.

Prune to Open Center of Rose of Sharon
 When you have removed the main canes from as close to ground level as possible (two cuts may be needed if canes are growing close together, making it hard to get close on the first cut), stand back and look at the canopy part of the shrub.

Determine which branches are growing inward, or rubbing against other branches, or show breakage or other damage. As well, prune out any weaker, smaller branches that will not produce healthy blooms yet will sap the shrub's strength if left in place. All of these should be pruned out.

Again, try to prune no more than one third of the length of any branch. Select a cane, look for an outward facing bud, and prune just above the bud on a 45 degree angle or slant.

Maintain or Control Height of Rose of Sharon
 Once the shrub's interior has been cleaned of dead or crossing canes, decide how high you want the shrub to grow. This depends on personal preference, location in the garden, and how tall you are, if you want to be able to prune without use of a ladder.

The height of this Rose of Sharon in the photo is fairly low, around 6 feet high, and can be pruned when standing on the ground. Note not all branches are the exact same length, but generally the same height. Where each cane is pruned depends on where the outward facing bud is on the branch.


Rose of Sharon After Pruning Mississauga Ontario in Spring
 After pruning, this Rose of Sharon has a neat, cared-for shape. Old, damaged canes have been removed, the interior of the shrub is open to sunlight and breezes that discourage fungus, and the plant is ready for spring fertilizing.

Rose of Sharon blooms on new wood, and regular feeding over the coming months will encourage lots of new growth and buds that will be a gorgeous show in mid to late August, about 4-5 months from now.

When Crocuses Bloom, Prune Rose of Sharon and Roses.
Here's another visual indicator of when to prune Roses and Rose of Sharon: Crocuses are in bloom. Blooming early spring bulbs indicate that spring is indeed on the way, even though days and nights are still cold.

Here's a video of the pruning this day:

Pruning Rose of Sharon




General Pruning Tips
These are good pruning tips for all shrubs, but do not prune Spring flowering shrubs and trees such as spirea, flowering almonds, cherries, etc., until AFTER they have bloomed this season.

Rhododendrons are spring bloomers, and will be pruned for shape and to remove dead wood in mid to late June. Rhododendrons also need spent blossoms removed after flowering, so it is a two-part process. Not all rhodos will need branches pruned, but all will need old blossoms removed.

Rose of Sharon August 2011

Rose of Sharon Full Bloom
Here are the Rose of Sharon shrubs pruned last spring. They are loaded with buds and blooming profusely in mid to late August, and now into September. Further shaping can be done, but best to wait until early next spring to allow for any damage to branches over the winter.

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