Itching to Garden

Three kinds of shrubs, three kinds of pruning

Potentilla before pruning

Heptacodium in bloom in August

Day 32

The Daily DuBrule

Beautiful days in February make all gardeners want to get outside and start working. What can you actually do right now? You can PRUNE! Before you drag out your electric hedge clippers, stop and read this pruning primer. I am talking about hand pruning. And only certain plants should be pruned now.

The basic concept behind when to prune is based on "old wood new wood". What that means is that there are two kinds of plants. Those that bloom in the spring, from now until mid-late June, set up their buds the previous year on old wood. Any pruning that is done now will cut off the flowers for this season. We're talking rhododendrons, azaleas, lilacs, viburnums, weigelas, mountain laurels, and a lot more. The time to prune this category of shrubs is right after blooming, usually around June. 

The second category of shrubs are those that bloom in the summer and fall on current year's wood that is produced this season. Examples are Potentilla, Callicarpa (beautyberry), rose of Sharon, mimosa trees, butterfly bushes, Caryopteris (blue mist shrub) and Heptacodium (seven sons tree). These are the plants you can work on now. In fact, with a good spring pruning to thin out and cut back old wood, the plant flowers much more profusely. 

Look at the picture of the Potentilla above. I start by going into the center of the plant and removing 3 or 4 old branches completely. This opens up the plant and allows light inside, thus encouraging fuller, bushier growth. Then I top it, usually cutting it back by about 1/3. It will have creamy yellow flowers starting in June and continuing until the fall. By using this pruning method, I have kept this plant the same size, blooming beautifully, for the eight years I have lived in my house.

The Heptacodium tree is about 15 feet tall now. It lost some branches in the snow storm last October. I am going to shape and prune it this weekend as it has no leaves and I can see its structure. It has sweetly fragrant clusters of white flowers in August, followed by coral calyxes that remain colorful all during the fall. This is a very cool tree to grow if you are looking for late season interest.

The top picture shows three different shrubs. The soft pink hydrangea is Hydrangea arborescens 'Invincibelle Spirit'. It blooms only on current year's wood and needs to be pruned now. The dark pink flowering shrub is Azalea 'Millenium', an upright, deciduous azalea that blooms in very late June. I can see the flower buds on it today. I won't prune it until after it flowers. The third shrub in the picture with the purple leaves is a smokebush (Cotinus). It blooms on old wood with puffy flowers that look like balls of smoke. I don't want to prune this now as the flowers are so beautiful. BUT, I lost a lot of branches on this plant during the snow storm and it has a funny shape. Plus, the more you prune it, the better the purple foliage becomes. So, I am going to prune part of it now to correct the shape and leave part of it alone to be able to enjoy the flowers.


If you understand the simple concept of "old wood new wood" you can prune your plants at the proper time and fall in love with the process. I am heading out into the garden as soon as I publish this post to soak up the sunshine and enjoy the gift of this beautiful day.