Bonsai: a reflection of nature, captured in miniature, as seen through the eyes and soul of the practitioner

Of all the aspects of bonsai care, root pruning has been the one in which I have made the most mistakes. When I first started I would just whack off one half to two thirds the root ball at the very beginning then begin trimming away more until the plant fit into the pot I had selected. I paid no attention to the size, shape, or position of the roots. I would like to pass on to you what little I have learned in the hopes that it might save you some costly mistakes.

As I stated earlier I am still pretty new at bonsai, but there are a few things I have learned about roots so far. They cover; the appearance of the visible roots, the condition of the root ball, and relationship between roots and the growth of the tree.

The first topic I will cover is the appearance of the visible roots. The term for this is nebari. The root system on a mature tree in nature radiates from the trunk firmly anchoring it into the soil. In bonsai you should seek to duplicate that by training the roots to form a nice radial pattern that appears to firmly grasp the soil. A tree without strong roots looks weak and unstable and therefore is to be avoided.

Another consideration is the condition of the root structure under the soil. Long stringy roots are not what you are looking for. In the process of survival the fine feeder roots accomplish the actual transfer of nutrients to the tree. Long stringy roots just take up space in your pot and do nothing to ensure the health of your tree. What you want is a fine system of small fibrous feeder roots radiating from the nebari under the soil.

Finally, you know that roots provide the tree with nutrients from the soil. Are you also aware that the roots receive nutrients from the foliage? There is a fine balancing act that goes on between roots and foliage that you must be aware of when pruning either roots or foliage.

The roots absorb nutrients from the soil and then send those nutrients up the trunk to provide for growth of the branches and foliage. The foliage then in return sends nutrients down to the roots to provide for their growth. Also during the dormant season the roots stockpile food for the coming burst of growth that begins in spring.

If you cut away too much of the foliage the roots cannot grow or store the necessary food for future plant growth and your tree will weaken and eventually die. If you cut away too much of the root system they will be unable to support the foliage and your tree will weaken and die. So you must pay close attention to how you maintain your root system to ensure the continued health of your tree.

There are two periods in the year when it is best to root prune, late fall and early spring. In late fall the actual growth of the plant may have ceased and the plant may appear dormant but there is still activity in the roots. They will continue to grow as long as the daytime temperatures remain above 55 degrees or so. If you root prune now you are not taxing them to provide nutrients for the tree, yet they are still in the process of growing and they can still recover from the stress placed upon them before they also go dormant during the winter months.

If you root prune in early spring the buds already have received enough food from the roots to open and grow new leaves. The roots can be cut back at this time and the new leaves will provide the food back to the roots to recover from the damage inflicted upon them by pruning them. It is inadvisable to root prune during the growing season because the tree is still in the process of growing and the reduced root mass will be overworked.

There are many things that determine when and how you root prune. One of them is the material you are working on, i.e. established bonsai, a tree grown from seedling, or newly acquired garden center stock. If it is an established bonsai you should only need to root prune if the tree shows signs of being pot bound.

I have only now just begun to grow my own trees from seeds, but mostly I have worked with garden center stock for my bonsai. When your grow your own trees from seed you can start training the roots to form a nice radial pattern from the very beginning. This is not the case with garden center stock. In garden center stock the tree has been allowed to grow unrestricted in its one, three, or five gallon container. The roots tend to be compacted and completely opposite of what you want in a bonsai. It may takes years to develop the kind of thick nebari that you want from garden center stock, but it can be done if you pay close attention to how you prune and shape the roots during transplanting.

One of the things you should be aware of is that a lot of the stock you buy from your local nursery is grown from cuttings. They will tend to have long stringy roots or lots of fine fibrous roots. Neither one is what you need in a mature bonsai specimen. In either case you have your work cut out for you. If your roots are long and stringy it will take years of cutting back the ends of those roots while you try to develop a fine fibrous root system. On the other hand if you have a fine fibrous root system you will have to select which roots you wish to allow to grow into your large roots and then wait for them to thicken over time.

Whichever case you are confronted with you can only do so much at one transplanting. You can only make gentle suggestions in the growth process and allow nature time to respond. Drastic changes in your root system will weaken your tree and possibly kill it. Believe me, I found this out the hard way.

I found the best way for me is to take a garden center tree and remove it from the pot and examine the roots to decide which case I am confronted with. I then put the plants into 10-inch bulb pans while I begin the process of training my roots. This also has forced me to take more time in the consideration of how I will shape my tree.

When it comes time for transplanting I gently comb out my root ball and trim back the long stringy roots to encourage more fine feeder roots closer to the trunk and then re-pot into fresh soil. I try to leave a few roots to grow long to become to future roots that will be visible from the surface, my nebari. The other long roots I trim back to force fresh new growth close to the trunk.

Root pruning is something I am just getting a handle on. I have killed my share of trees because I didn't have a clue about how to take care of them. While it seems I have provided a lot of information here, I have only brushed the surface. I suggest you seek out as much information on the care of roots as you can. I am still learning on a daily basis.

Bonsai is an art form in which both your trees and your knowledge about their growth processes continually grows. As you learn more you begin to realize that there is so much more to learn and apply. But if you get the basics down you will at least be able to maintain your trees in a healthy status while you learn the more advanced skills. I hope I have provided something that will be of use to you.