Juniper bonsai come in a couple of different forms. You have most of our native species that are running junipers and you have the Japanese species that are mounding junipers.
Bellow I am going to discuss a bit about the care of Rocky Mountain Junipers and Shimpaku Junipers. Some techniques are suitable for both types. They just grow differently so the timing is different.
When we talk about running junipers, what we mean is that the juniper will extend before it mounds. It sends out whips and then you will see it grow interior growth and mound.
Some species of running junipers are listed below.
- Rocky Mountain Juniper
- Sierra Juniper
- California Juniper
- Western Juniper
Mounding junipers will grow nice dense puffs of growth before it sends out extensions. Below is a list of a few of the mounding junipers that we use in bonsai.
- Shimpaku Junipers
- Procumbans Juniper
- Needle Juniper
Rocky Mountain Juniper Bonsai
(Note: I will talk about Rocky Mountain Junipers as running junipers can be handled similarly)
The Rocky Mountain Juniper is a running juniper. The growth will extend or grow whips before it will form a more dense mounding growth at the base of the whip.
Rocky Mountain Junipers prefer to be pruned mid to late summer after the foliage has hardened off. If you let the tree grow all year to get some extension to the branches you could prune in early spring but you need to protect the tree from freezing temperatures. Pruning in early spring will result in all of the stored energy going to a smaller amount of foliage. This will cause an explosion of growth in those branches and could cause coarser growth.
When you do prune, make sure to cut cleanly with scissors. Never pinch a juniper.
When you have a Rocky Mountain juniper that has its main structure and secondary branches set, you will be working on the tertiary branches. At this stage of “finished” bonsai, you want to be pruning in early to mid-summer. Pruning at this time of year the tree has pushed some of its energy so the resulting growth will be shorter and more compact.
One strategy to use when wiring a Rocky Mountain juniper is to make tiers with the whips or longer branches. This can create pads of differing heights. Another strategy is to fan out a long branch with smaller branches on the outside of a bend. This can create a pad as well.
One thing about junipers is that the strength comes from the foliage and vascular system. The tighter and more compact the growth on your juniper, the more ramified your root mass will be.
I have a progression page for my own Rocky Mountain Juniper.
Shimpaku Junipers (Juniperus Chinensis)
(note: I will be talking about Kishu, Itoiagawa, Toyama varieties of Shimpaku as they all can be handled similarly)
Shimpaku junipers are a mounding juniper. This means that they will grow dense at the folier base before the growth will elongate.
Late summer or early fall is a good time to do maintenance work on our Shimpaku junipers. Things we want to do to maintain our junipers are as follows.
- Remove the growth coming out of the crotches of branches.
- Clean the bottom growing needles on the branches.
- Trim the interior spent growth.
- Cut back the extending growth.
Remove the growth coming out of the crotches of branches unless we are going to be using it for ramification or to replace a branch. This growth will take the energy that we want our other branches to have. This can weaken the branch and cause our growth to be leggy and not so compact.
Clean the bottom growing needles because this growth is using more energy than it is producing. Being shaded out by the growth above, it can not photosynthesize efficiently. Meaning this growth will be weak. We also remove this growth because it gives the bottom of our pad’s definition and shows separation from the other pads around it. Removing this growth also allows light and airflow to the pads under it.
Trim the interior growth that is old and spent. This growth also uses up more energy than it can produce, so it is not necessary to keep. Another reason to remove this growth is that it allows for air and light to penetrate the interior of the tree. This helps produce further back budding on the branch.
Cut back extending growth to a strong secondary or tertiary piece to the shape of your pad. This is necessary for the health of the branch but also introduces bifurcation. If of course, you are trying to let the branch grow and get longer than you would remove older foliage at the base of the extension and allow it to grow.
A good tip for any juniper is when you are cleaning the inside growth off of a branch, remove the growth on the first 1/8th – 1/4″ of the branch. This growth will never be used. It allows for more light and air to penetrate the tree as well as giving you a nice clean area to place your wire at the base of the branch.