By Neil Padbury

www.shibuibonsai.com.au

Nebari is a Japanese word that describes the roots that can be seen on the surface. You may also come across the related term tachiagari which refers to the lower part of the trunk and where the trunk widens out to join the surface roots – nebari.

Surface roots help us to see age in a tree. Young trees don’t usually have roots visible. They are all still under the soil but as the shallow surface roots grow and thicken they are likely to start to show up above soil level. The older the tree the more roots we are likely to see on the surface.

Anyone who has had to mow under an old liquidamber or elm tree will immediately know what I’m talking about. The older the tree gets and the more you mow the larger and lumpier those roots get.

Bonsai roots that are completely exposed or sticking up at odd angles do not necessarily constitute good nebari. The roots should look natural, like they actually grew there. Sometimes roots can be exposed by erosion in nature but they don’t generally grow up out of the soil then back down again. In the vast majority of cases we should not see any spaces between the roots and the soil because that just seems to make the tree look unstable.

There is a style of bonsai that features completely exposed roots. Neagari is the Japanese word for exposed root bonsai style which are probably modelled after the types of trees seen after erosion has left the tree sitting on stilt like roots but that’s another story entirely.

Good nebari also gives us an impression of stability. We can see the roots spreading out in all directions giving our minds the impression not only of great age but also stability. A tree with wide spreading roots is likely to survive storms and other natural catastrophes.

Some features of good bonsai nebari include:

• Just the upper surfaces of the roots showing above soil level.

• Even sized roots rather than a few really thick ones mixed up with finer roots.

• Roots spreading out in all directions.

• Roots spread out evenly rather than crossing over and tangling with each other.

• All roots at the same level. Try to avoid having one or more starting higher than the others.

• Roots that divide and spread evenly as they grow away from the tree.

Naturally shallow rooted species like pines, maples and elms do develop these surface roots as they grow in the forests and it is expected that our bonsai should also show good nebari to give that sense of age and stability.

Not all trees show nebari. Some mountain trees like junipers tend to grow deeper roots for stability so they don’t often have roots showing on the surface. In bonsai we still try to show the surface roots of junipers where possible but nebari is not anywhere near as important for junipers as for the naturally shallow rooted species.

How to develop good nebari

Root pruning is the number one technique to help develop good nebari on our bonsai. The earlier you can start the better the results tend to be. Prune off as many vertical roots as possible at every repot session. When we remove downward roots the tree has to rely more on the shallow lateral roots that are left so those roots grow bigger more quickly. As a bonus the base of the tree tends to flare out into those roots making the trunk seem even older.

Just having 2 or 3 big thick roots sticking out of the trunk is not really good nebari. We really want lots of even sized roots so more root pruning is required. By cutting the lateral roots short we can encourage the tree to grow even more roots out of the trunk. The pruned roots will also sprout new roots from the cut ends and that will help produce roots that divide and spread.

Also remove roots that cross other roots and the ones that grow in odd directions. As these roots get thicker they will definitely start to distract the viewer’s eye when they look at your bonsai. An evenly spread nebari without distractions will definitely lift the appearance of your bonsai as it matures and ages.

Where a trunk has a gap where there are no roots they can often be encouraged to grow by wounding the bark where you want new roots. Cut a strip of bark out or drill a series of holes through the bark then use a rooting hormone and cover the area with sphagnum moss or potting mix. If the area is kept damp it is likely that the tree will grow new roots from the wounded areas. These methods work better if the holes are filled with something to stop the tree healing over before roots can grow. This gives rise to the ‘toothpick’ method where the holes are plugged with matchsticks or tooth picks.

Roots can also be grafted onto trees. It is possible to graft roots direct in places you want them but it is more common to graft a seedling in the spots you want roots then when the graft has healed cut the top off the seedling leaving its roots grafted onto the trunk of your bonsai.

2 methods are currently used to graft roots:

1. Approach grafting – Cut a slot in the bark of your tree were the roots are needed. Slice the bark of one side of your seedling right down near the roots. Place the seedling in the slot so that the wounded parts meet then tie the seedling tightly to the main tree. Nails or pins are often used to hold approach grafts in place while they heal. As both the main tree and the seedling can grow on their own roots they will both stay alive while the graft knits so accuracy is not altogether necessary for this to work. After the graft has healed together well the top part of the seedling is removed leaving new roots feeding the bonsai through the graft.

2. Thread grafting – Drill a hole through the root or trunk were you want new roots. Thread a tall, skinny seedling right through the hole so its roots are now where you need new roots. Hold it all in place and seal the holes to keep water and air out while the tree heals up. Again, both parts can exit on their own roots for as long as the graft takes to completely heal. As the hole in your tree heals and gets smaller an as the seedling grows and thickens the 2 parts will squeeze together. Eventually the cambium of both trees will unite and sap can flow from one to another. When you are confident the grafts have united the top of the seedling can be removed leaving the roots as a new part of the bonsai.

There are some pictures to illustrate both thread and approach grafting to add roots toward the end of this Shibui Bonsai blog article.

Sometimes when existing roots are not suitable we can start the root system all over again by layering the entire trunk. Air layering can be used to grow new roots higher up the trunk or on a branch. Air layering can also be used on a garden tree to make a new tree to plant or to grow as abonsai. Air layering usually produces lots of good radial roots that will develop into a great, spreading nebari in time. Here’s a Shibui Bonsai post showing how to air layer for bonsai.

Where the existing trunk is good but roots are not suitable for bonsai we can layer close to the roots. The ringbark or tourniquet methods are both effective and will usually produce lots of radial surface roots. When good new roots have grown simply saw off the old root system and plant your tree on its new roots which should continue to grow and thicken into lots of strong, spreading roots.

At shibui Bonsai I often start new trident maples using a special technique that makes them create their own layered lateral root system. Seedlings are threaded through holes drilled in sheet metal disks then planted so the metal plate is just under soil level. As the seedlings thicken the trunk is restricted where it passes through the metal plate. When sap flow is restricted the trees make new roots just above the plates. Those new roots tend to grow all around the trunk and are kept horizontal by the metal plate giving a perfectly flat, well spread nebari with little work on my part. See some photos and tips in this Shibui Bonsai post.

This trident maple was photographed at Kokufu-ten, one of Japan’s premiere bonsai shows. It is a good example of ‘pancake’ nebari

Some people think that is wonderful while others see such nebari as over the top. What do you think?

Like all other aspects of bonsai nebari tends to go through fads and phases. Some Japanese growers have developed large plate like masses of fused roots, particularly on Japanese maples.

Still not sure if nebari is really natural? Check out old trees in your area to see if they have started to show natural surface root nebari.