Thuja occidentalis Slab Planting

The other day I planted this Eastern White Cedar (Thuja occidentalis) on a slab I picked up from Aichi-en in Nagoya, Japan. I believe the slab is made of concrete, although the artist did a very good job of giving it a natural form and texture.

I had the help of a friend who has much more experience planting trees on slabs than I do. I was expecting to have to make a retaining wall out of muck like Bjorn does for a white pine in this excellent video, but I learned that this step is completely unnecessary with healthy Thuja because of its incredibly dense root characteristics.

Unfortunately I didn’t get many pictures of the process because I was busy working on the tree 🙂 However, the key points to planting Thuja on a slab are as follows:

  • The material should be well established and have a dense, fibrous rootball. Most Thuja can produce this in two years of growth in a coarse bonsai soil such as a lava rock or pumice based mix.
  • Do not disturb the rootball any more than is necessary. In other words, don’t rake the whole thing out. This will weaken the structure of the rooball and will make it difficult to keep it intact once planted on the shallow stone.
  • Remove thick, downward growing roots.Thuja collected from rocky areas typically have few of these, as was the case with this tree. Once the rootball is shallow enough, leave it alone.
  • Trim long, thick roots that extend beyond the desired perimeter of the rootball. Excessively long fibrous roots can be tucked underneath the rootmass once it is placed on the stone.
  • Tie it in tight. Drill more holes if necessary.
  • Work in soil where necessary, If the rootball is dense and was undisturbed, relatively little soil will need to be worked in near the trunk.

"Before" (this is actually a picture from last summer).

The rootball tied into the stone. I'm guessing only about 25% of the rootmass was removed for this planting.

The result. I am happy with the stone and the more upright planting angle. This is actually closer to how it was growing in the ground. This tree still has a lot of development ahead of it, so there is no point in adding moss. No top pruning was done. The tree just looks thinner because it shed its foliage last fall, after the first picture was taken.

Grafting Hinoki on Thuja (Arborvitae) Part 2

See here for Part 1.

My Thuja are starting to lose their winter colour, so I figured now was as good a time as any to make my first attempt at grafting hinoki foliage to this old bare tree.

Ready for grafting.

Ready for grafting.

The type of graft I attempted was a type of side veneer graft, as shown in the image below.

Side veneer graft.

Approximate size of the scions used. Hopefully they aren't too big? I chose the size based on images I've seen of people doing the same type of grafting on juniper.

Approximate size of the scions used. Hopefully they aren’t too big? I chose the size based on images I’ve seen of people doing the same type of grafting on juniper.


A (very tight) elastic band was used to initially secure the scion to the rootstock. This is a nice trick I learned at a recent grafting workshop. It allows you to still "tweak" the position of the scion after it is secured to the tree, to ensure that the cambium is aligned properly. There are special UV resistant elastics designed for this job, but I just used old kitchen elastics. A tight layer of teflon tape went over the elastic to protect the wound.

A (very tight) elastic band was used to initially secure the scion to the rootstock. This is a nice trick I learned at a recent grafting workshop. It allows you to still “tweak” the position of the scion after it is secured to the tree, to ensure that the cambium is aligned properly. There are special UV resistant elastics designed for this job, but I just used old kitchen elastics. A tight layer of teflon tape went over the elastic to protect the wound.

Three grafts in total were attempted. One was covered in a clear plastic bag. For another, the scion was wrapped in parafilm (which apparently breaks down quickly enough that the scion can actually grow right out of it). The last one was left unprotected. Professional propagators don’t wrap their scions in anything, but they also have fancy greenhouses to control their environment. We’ll see what happens.

To be honest, I am not feeling very confident about these grafts. I did the best I could, but I feel that I am at a big disadvantage without having a greenhouse. But nothing ventured, nothing gained – right? If these fail, I will try approach grafting and possibly some more side veneer grafting in the late spring.

Fingers crossed!

Perlite as a Bonsai Substrate

Perlite is readily available and cheap, but I’ve never really used as a soil component because it is too lightweight (floats/doesn’t weigh down the pot) and it is really ugly.

However, I’ve noticed that there seems to be a practically religious following in Italy of bonsai growers who swear by using pure perlite for rehabilitating recently collected yamadori.

As evidence of the powers of perlite, check out these amazing pictures taken from this thread on the forum Master-Bonsai.com, which is administered by Andrea Meriggioli (a young professional in the very serious Italian bonsai scene):

Pinus nigra... once of those "oops" trees that did not exactly come out of the ground as expected. It is amazing that Andrea even bothered to try with this tree.

As far as pine goes, this is practically no roots.

Planted in pure perlite

Here it is budding out. The tree is still alive today!

It even has roots coming out of the pot in the same growing season as it was planted.

I’m not sure if perlite can be given all the credit for this pine pulling through. Andrea also used a number of tonics when he planted the tree (“radimix, bioxim, and antym kombu40 etc.”), whatever that stuff is. Nevertheless, it is an impressive story.

Tired Old Potentilla fruticosa

The potentilla that is the subject of this post was collected about 10 years ago by a friend of mine. I have admired this tree for some time, as potentilla’s of this size and drama are quite rare. When I had the opportunity to buy it for a reasonable price last year, I didn’t hesitate!

Potentilla fruiticosa yamadori


However, this tree has some serious issues and serves to illustrate some limitations of potentilla for bonsai. In a recent post, I said that potentilla are one of my favourite species. They are certainly not perfect, however. Many people will refer to the limited longevity of potentilla. While they are hard to kill, their weedy growth habit is subject to dieback. Their biggest issue, however, is wood rot. This tree is a perfect example of the issues that arise with potentilla over time.

When designing potentilla bonsai as a deadwood species, you must be very conscious of the soft wood. It is nowhere nearly as robust as the deadwood of other deadwood species such as Thuja and Juniperus, and requires extra care. This means treating at least once a year with a penetrating wood hardener, and keeping the deadwood clean and dry. This is the product I like to use.

These techniques were not applied to this potentilla over the last decade, and as a result it has lost much of its structural integrity as a result of rot. Some of the fine jins near the base of the tree also crumbled away when I first laid hands on the tree last summer. The tree is literally falling apart. To make things worse, was planted in a very mucky organic soil mix which takes a long time to dry out.

The purpose of this spring work was mainly to take steps to minimize the advancement of the rot by doing the following:

  • Remove as much of the rotted wood as possible
  • Bareroot the tree and replace the soil with a coarse inorganic mix
  • Plant the tree more upright so that the deadwood is far away from the soil surface
  • Treat with limesulfur, then wood hardener

Crevices such as this are highly at risk of rot, especially if they are not kept clean and dry.

This organic soil mix holds far too much water. This rotted the jins that (used to) lay on the surface and also creates too much humidity for the deadwood that lies above the soil. It is worth noting, however, that the tree grows fine in this soil. Potentilla will grow well in almost anything!

The video clip below shows the extent to which the rot has compromised the structural integrity of the tree.


This is the new pot. It is a yamaaki pot with some signs of age. It is far from ideal, but I think it is a slight improvement on the current pot. I think this tree is ideally suited to a crescent stone, but I have not been able to find the right one yet!

After much struggling, I decided to break the pot. The unusual shape made it very hard to get the tree out and, given how fragile the tree has become, I did not want to pry on it too hard. This pot was made by the previous owner and he warned me that I might have to break it - sorry! :)

Barerooted with the hose and trimmed. You can see that the root system is strong despite the difficulties the tree has presented to the bonsai design.

The tree is so "floppy" that it had to be tied to itself in order to achieve the desired angle. This guy wire is hidden at the back of the tree and can be adjusted if needed.

Thats it for now. Much cleaning and wood preservation still needs to be done, but I think that the deadwood is much safer now than it was before.

The back of the tree is quite interesting as well. As the structure of this tree continues to deteriorate, I am sure that I will have to keep other design possibilities in mind.

Twisty Potentilla Clean Up

Potentilla fruticosa (Shrubby Cinquefoil) is one of my favorite species for shohin bonsai. In rocky northern regions, interesting specimens are easy to find which can be yanked out of the ground like turnips with a nearly 100% success rate. They are not a particularly common subject, but can still be found in bonsai gardens in most temperate regions of the Northern Hemisphere. I’ve seen amazing specimens coming out of North America, Europe, and Japan.

This is one of several small potentilla I collected last spring. In the proper soil they will quickly develop a fibrous root system and are almost always ready for rootwork the following year. Unfortunately (like junipers) collected potentilla may stubbornly hang on to a few long thick roots that can be difficult to chase back. Cutting back roots has to be done with great care because the compartmentalized nature of their growth can lead to dieback of live veins that are critical to the design of the bonsai.

I collected this tree because while crawling around in the mud I caught a glimpse of a twisting trunk hiding beyond the weeds and flakey bark. The initial clean up is one of the most important steps with collected potentilla, because you never really know what you have until you remove the bark and punky wood.

So here we are, nearly one year after collection, and I finally get to see what I brought home with me!

This shaggy mess is typical for collected potentilla. The paper-like bark hides the most interesting features of the tree.

It seems that there is some potential with this little tree, but it is impossible to tell until further cleaning is completed and the nebari is exposed.

The flakey bark peels away easily with tweezers or using your fingers. It is also necessary to scrape and dig in the many crevices of the tree, where dead bark becomes trapped and rots between the fusing stems.

Once the bark is removed, the dancing nature of the trunk becomes clear. It is also clear that this tree is the result of several stems which have fused together at the base. The cleaning process is not nearly complete. Getting all the old crap out of the crevices takes lots of time and patience, and will probably take another couple of lazy summer afternoon sessions of picking and scraping. Nevertheless, the work done here is sufficient to map out the design.

The next step for this tree will be rootwork in the next few days. If the root system does not need major operations, it will grow strongly and I should be able to cut it back hard in the late spring or early summer. Potentilla backbud profusely and reliably, but they need to be cut back quite ruthelessly. After that, the deadwood work will come. I intend to reduce the live veins to emphasize the twists in the trunk.

It is worth noting that potentilla are ridiculously hardy, and I find they are always the first species to wake up in the spring. Some of mine are already leafing out, 2 weeks earlier than normal due to the mild winter we experienced. I usually repot them when the leaves just begin to emerge, although this is definitely not the only time they can be repotted.

On to the next one!

Cedar (Thuja) Leafminer Damage

Thuja occidentalis (Arborvitae) is incredibly disease resistant, and there are only a handful of pests that are of any concern to the bonsai grower. One of those pests is the larvae of a tiny moth called the cedar leaf tip miner.

The following excerpt is taken from a University of Guelph Pest Diagnostic Clinic Factsheet on Thuja occidentalis:

Cedar leafminers are tiny moths native to Canada. Damage is caused by the small larvae feeding within the scale-like leaves of cedar. An infestation is usually first noticed in the spring when the tips of some branches begin to bleach and brown. Heavy infestations can cause severe thinning of the foliage.

The article goes on to say that the disease is not a major concern but, for bonsai growers, it can be aesthetically displeasing and can also weaken the tree if left untreated.

The tree below was collected in late April 2011. I suspect that its recovery left its defenses down, and by August the leafminer had established itself.

Cedar Leafminer Damage on a small (25 cm) Thuja occidentalis. The damage is minor, but enough to have affected the recovery of this recently collected tree.

Treatment of leafminer is relatively simple. Prune away the damaged foliage, and keep the tree in full sun to promote the recovery of the plant’s defenses. A light application of a systemic insecticide such as imidacloprid will seal the deal.

As a preventative measure, Reiner Goebel recommends treating Thuja with a systemic in the spring to avoid unexpected infestations of leafminer.

One month later, the tree is sparse, but happy. The tree should be much stronger through 2012, and I doubt the leaf miners will return. It may even be ready for its first wiring by the summer. Had it not been for the leaf miner, the tree probably could have been wired this spring.

Growth Rate of Stressed Thuja occidentalis

This is not a rule, but you can see that Thuja in some stressed conditions (especially drought, poor soil, and crushing ice) grow as little as 2 radial centimeters every 40-50 years. This promotes the development of great bark and deadwood character in small trees. Good junipers cannot be collected in my part of Canada, but Thuja has much of the drama that is so desireable in Juniper bonsai, combined with a unique ruggedness.

The picture of the rings is from where the old top of this tree was cut back after collecting (not a dead tree 🙂 ). This tree was sold last year.

Old Thuja bark

Grafting Hinoki on Thuja (Arborvitae) Part 1

Many people think that the foliage of Thuja is untameable and unsuitable for bonsai. This is not true – a very refined image can be produced with the native Thuja foliage, especially for medium to large bonsai.

However, there is always the possibility of grafting the more fine hinoki foliage on if you are truly dissatisfied with the native Thuja. The two species are, after all, quite similar. While hinoki has better foliage characteristics, thuja has better vigour and wild specimens have incredible deadwood features. When I showed pictures of my collected Thuja to Junichiro Tanaka (owner of Aichi-en in Nagoya), he described them as “Hinoki Juniper”.

But even though I am content with the native foliage, sometimes grafting is necessary. Take this tree as an example.

When it was collected, I planned on building the bonsai from the branch closer to the trunk. The longer section was to be cut off when the tree recovered.

The long, far away section of foliage had no purpose for the bonsai design.

Why didn’t I cut it off when I collected it? Well, I’m not totally convinced by the “balancing the roots with the shoots” idea. It seems like common sense that leaving more foliage will give the tree more strength to produce new roots, as long as you can minimize transpiration with misting.

Well, it looks like I ate my words here. The most important branch died, of course. I think this is because the roots supporting it were damaged when collecting. Cedars have a very “divided” lifelines that are distinctly attached to roots. If I killed the roots that supported that branch, there was not much hope.


The trunk is nice enough that the tree is worth setting aside as a grafting project. I have never grafted cedar, and this will be an exciting project for this year (and maybe a few years to come). Nick Lenz has a “hinoki cedar” that is rather famous in the Eastern North America. It took him something like 4 years to completely replace the thuja foliage with hinoki. I believe he used thread grafts for this (yes I know… sounds insane) and Chamaecyparis obtusa ‘Nana’ (dwarf hinoki).

An older picture of Nick Lenz's "Hinoki Cedar", created by grafting Dwarf Hinoki onto a collected Thuja occidentalis trunk.

I am not planning on using thread grafts, nor am I planning on using Dwarf Hinoki. I will try two types of graft – approach graft and bud graft using Chamaecyparis obtusa ‘Kosteri’. This variety seems somewhat more vigourous that ‘Nana’. The foliage is not as compact, but it is still very fine, dark green, and somewhat less curly than ‘Nana’. Hopefully the greater vigour of Kosteri will accelerate the grafting process. Check back soon for updates.

'Kosteri' Hinoki foliage.