If your forsythia, rhododendron or weigela has no flowers it’s most likely caused by cutting it back at the wrong time. Knowing when a shrub blooms will solve the problem.
In Rhode Island (USDA Zone 6), the forsythia blooms in April. If it was looking shaggy last July and you sheared it back, you can bet that you won’t have much of a bloom this year.
Most Spring flowering shrubs, like forsythia, start growing their flower buds for the next season within just a few weeks of finishing the current year’s blooming. Remember this fact and you’ll know which shrub to prune when, and you’ll never prune at the wrong time again.
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Spring Flowering Shrubs
#5. lilac (Syringa)
#6. Mock orange (Philadelphus)
For shrubs that blooms in the Spring, do your pruning within 2 weeks after the shrub has finished flowering and then leave it alone for the rest of the season.
If it’s absolutely necessary you can remove a few straggling branches but cut them out one-by-one on an as-needed basis so the flowers on the rest of the shrub remain. Do not shear the entire shrub at this time or all the blooms will be cut off, ruining next season’s show.
Summer or Fall Flowering Shrubs
#3. Butterfly bush (Buddleia)
#4. Blue mist shrub (spigela)
#5. Rose of Sharon (Hibiscus)
#6. Summersweet (Clethra)
Shrubs that bloom in June, July, August or September can be pruned in late winter to shape them up for the coming season. But don’t wait until the middle of Spring to do it because most of the shrubs in this group start making the season’s flower buds in the Spring.
Cut these shrubs back as hard as necessary just as they begin to leaf out. As with the Spring-flowering shrub group, selective pruning throughout the growing season is okay – just don’t take out the hedge shears to do the job. Use small hand clippers or loppers to just cut the branches that need to come off.
Best Time to Prune Evergreens
#1. Yew (Taxus)
#2. Juniper (Juniperus)
#3. Pines (Pinus)
#4. Spruce (Picea)
These should be pruned when they are dormant. Here in USDA zone 6 that means mid-December, January and February. The act of pruning kick starts a chemical reaction in the plant that sends out new growth.
When the cuts are made just before Spring the result is lush new foliage and branching in the coming season. If the cuts are made in late Summer or Autumn the new growth that emerges will probably be killed by frost before it has time to mature enough (aka harden off) to survive the winter. This rule also applies to deciduous shrubs like:
- burning bush (Euonymous alatus)
- Harry Lauder’s Walking Stick (Corylus avellana ‘Contorta’)
- shrub dogwood (Cornus alba)
A Word About Hydrangeas
It’s important to know what variety of hydrangea you have to determine how to prune it. Generally, the older hydrangeas (Hydrangea macrophylla) can be pruned after flowering. The newer varieties such as Endless Summer ™ (also H. macrophylla) hydrangeas are bred to bloom on new or old wood so timing doesn’t matter as much.
Hydrangea paniculata, which is popular in tree form, blooms on current season growth so it can be cut back just before Spring comes. When in doubt about what type of hydrangea you have do your research and use a very light hand if you aren’t sure.