We often have clients asking why their flowering shrubs bloom very little or not at all. After ruling out incorrect sun exposure and over or under fertilizing, we ask what time of year the shrubs were pruned. More often than not, it is found that the shrub in question was pruned in fall or winter. This is the problem!
Spring blooming plants set flower buds on the previous year’s growth, known as “old wood”. If the shrub is pruned before it blooms, the buds get cut off, thus no flowers. So, when do you prune? Right after the flowers fade. This gives the plant the rest of the season to form buds for next spring.
Aside from removing the spent flowers, this is also the time to correct shape and control size as well as making a few rejuvenating cuts.
To get the shrub to the size that you want it for the rest of the season, cut it back 6-18 inches further than that size. When the new growth is put on, it will then be at the desired size. The rate of growth determines the amount to cut back. For example, mature lilacs are vigorous growers and should be cut back 12-18 inches. Keep in mind, some shrubs, especially those with a fountain shape such as Bridal Veil spirea, can be left mostly alone providing they are planted where they can reach full size.
All flowering shrubs benefit from removing a few of the oldest stems by cutting them back as short as possible. These can be identified by their thickness and the appearance of the bark, which is rougher and duller than their younger counterparts. Called a rejuvenating pruning or cut, it allows space for vigorous new shoots and opens up the shrub for better air circulation and sunlight, and should be done every year or two.
So, what about shrubs that bloom on old and new wood such as Endless Summer hydrangeas? Providing you protected the stems over the winter, they will bloom in late spring on the old wood, then continue to bloom on new wood. When the old wood flowers fade, deadhead just down a couple leaves from the flower. On mature plants, thinning a few of the oldest stems after the first flush of blooms keeps the shrub fresh and vital.
If you want to enjoy spring bloomers indoors, feel free to cut stems of just-emerging flowers, and split or lightly crush the cut ends before putting them into a vase. This allows the woody stem to take up water. Now you can enjoy the heady fragrance of lilacs and sunny sprays of forsythia and get and head start of your spring pruning!
Thank you for reading, and if you have any questions or comments, you can comment below or contact us on our Facebook page—New Leaf Nursery-Hayden, or better yet, stop by and see us in person!
