Kiryuzuna is the superior top dressing

I messed around with top dressings for my trees this spring. In previous years the top layer was the same Boon’s mix that was throughout. I felt it was time to improve on that…

Warning! The following is a pedantic discussion of substrate and strata!

After many years of trying, I gave up on attempting to introduce live moss or moss spores on the top of my substrate. If moss grows there naturally, I let it spread, but I am no longer actively trying to propagate it on all my trees. I have mossed up a couple bonsai for temporary show the past few years at the regional agricultural fair using collected clumps, but that is it.

In an attempt to elevate my game, this spring I added milled sphagnum tossed with basic Boon’s mix in the top layer of my soil. My observations lead me to believe that many enthusiasts don’t need the extra step of sphagnum! Milled sphagnum is bulky, unsightly, unstable, and it makes it almost impossible to know what is actually happening with moisture in your smaller shohin and mame pots. It is an essential medium for establishing root growth in dug up yamadori and also as an antibiotic, but as a surface moisture retention system it is dysfunctional. Sphagnum obviously does nothing for root ramification when mixed into soil, either.

Deciding to eschew the sphagnum for my remaining trees, I opted to use straight pumice, fujisuna, or kiryu, on top of my bonsai. Fujisuna is a black lava available in 1/8" size particles. I had thought that the black might allow the pot and tree to speak more prominently and without any distraction, but instead the black made everything look inorganic, bleak, and gothic. Additionally, it is difficult to gauge water needs based on the darker appearance. There also might be a risk that black will be too hot for some trees left in the sun. So, I am slowly switching the fujisuna out on all the trees I used it on.

Aesthetically speaking and as an indicator of dryness, the white of pumice is just as bad if not worse than black. If you can get small grain Hyuga or Ezo pumice, that might be better, but I’ve never worked with those specific Japanese varieties before.

Lastly, I tried kiryuzuna. “Kiryu”, as it sold, is a smallish sharp river (sand). It is similar in color and price to Akadama. Both Akadama and Kiryu can be used as visual clues to the dryness of a pot. However, Akadama breaks down with repeat watering and it needs compounding pressure to keep from deteriorating prematurely. Kiryu does not break down and does not need to be compacted. That makes it perfect as the loose amendment on the top layer! It is such a small grain and pleasing appearance that even mame can be topped off with Kiryu.

The color variations of kiryu when your bonsai are wet, to damp, to dry, are very easy to discern. I will attach photos to show what I mean.

While this substrate component works well for me, I also operate out of my home and keep bonsai of every size from 2" mame pots to 24" yamadori pots.

If all your trees are all one size, or are on an automatic watering system, or you water on a schedule (shame on you) maybe kiryu is an unnecessary expense. Personally, I keep 100 trees and I like easy-to-spot advance warnings of when I need to water each bonsai.

Here’s what it looks like:
Saturated [just watered]

Moist [no need to water]

Drying [water soon]

Fully Dry [time to water immediately]

If you are concerned about deeper pots retaining more moisture at the bottom, don’t be. First, the lateral roots near the surface are what should be the focus on protecting and promoting at all times anyway. Deep roots in deep pots are fine to run a little moist as long as you are using inorganic substrates like Boon’s or Kanuma. If you doubt me, read Walter Pall’s article on the myth of overwatering.

I think Walter might overstate things, but the idea is if you have free-draining substrate, it’s ok to be a little moist. Unless you are sitting your pot in a deep drip tray or suiban, there should be no standing water to rot or boil roots (on brutally hot days). Rot or “trench foot” in bonsai occurs most frequently in pots with gobs of organic soil, no drain holes, or during the dormant period. The latter is more often in Western species like Ponderosa pine. While I keep bonsai on the wet side in the late spring, all summer, and early fall; during the rest of the year I limit water to all my trees for protection of the roots and foliage reduction. That means keeping my trees covered from rain and snow in the off-season and only watering them manually when needed. I am excited to have the kiryu for this coming winter to more effectively manage my moisture on a tree-by-tree basis. I lost one old Rosemary due to thirst last winter. I would not make that mistake again with a barometer like kiryu.

As mentioned, Kiryu costs about the same as Akadama - which isn’t cheap! But, as a top dressing, you will be surprised at how far a small bag will take you.

All of this might be basic information for some people who have been at bonsai longer or better than I have. However, it is a new revelation for me and one I felt compelled to share.

No offense to proponents of sphagnum like Ryan, but he is keeping a lot more trees than I am - the majority of which are oversized. Those factors may mean that milled sphagnum mixed into top dressings are more effective. Not for me, though. Make mine Kiryu. Straight up!

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Hi @Joe_Perry,
As with all things Bonsai, I am learning to first ask “what am I trying to accomplish?”
Top dressing can be applied aesthetically, to aid water/oxygen balance, to stabilise, to increase volume, to deter pests and I’m sure many other reasons.
I’m a UK grower, and this year in my area, we have found that moss growth has been poor coming out of the winter. At my club show a few weeks ago, lots of displays had fine akadama top dressing.
The one thing I was told, and have found to be true, is if you want to grow moss on a bonsai pot, the best place to get it is from a bonsai pot. When I repot, I save the moss for top dressing.
In my garden at this time of year I have a problem with young blackbirds, who love to pull all the moss off (pillocks!). Sometimes I have to put mesh over the moss to keep them off.

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Sorry for my naivete, but doesn’t the miss dressing also act as a filter for ferts and as a light blocker to allow the use of 100% of the container for root growth? Does kiryuzuna satisfy these needs as well or is that sacrificed?

I’m having a lot of issues with my top dressing as well. Where are you buying your kiryu?

Ryan’s top dressing is 1/4” ground sphagnum with ground up dried common local moss. The number one purpose of the topdressing is to stabilize the soil surface so that roots will grow. Ryan soaks the sphagnum in black dye prior to grinding to improve aesthetics. He sells the black dye in the online store.

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The Mirai top dressing grows decent very fine moss. I am happy with what I have seen so far. My dry environment here eats moss for lunch. The top dressing DOES enable better ROOT growth.
I have always grown moss on my bonsai surface soil. (40+ years) Only recently changed to (variations of) 1:1:1 soil. Without a top dressing, moss never gets a hold. My SMALLER bonsai survive the heat better with moss to protect the roots.
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Kiryu is (application specific) bonsai media. Still would need a surface treatment to grow moss. Very fine soil of some kind; and inoculation with moss. I’ve always used small tufts of green moss implanted sparsely. Fills in very quickly. Then, it’s a matter of slowing it down…

Hi Joe, interesting thread.

I have found in most cases that a sphagnum moss top-dressing just wasn’t working out for me, much as I wanted it to! I did exactly as Ryan instructed, down to the dyeing with the same brand of Sumi ink as well.

What I found happened for me is the sphagnum would form a crust on the surface which would usually crack and lift off the soil in places. The soil under the sphagnum layer was often still moist enough, so to keep the sphagnum constantly damp (so it wouldn’t crack and come away from the soil) would feel like I would be watering more than necessary for the trees.

I was considering either replacing with something else or re-top dressing with sphagnum (perhaps I applied it too thinly or thickly). Now I’m thinking I’ll give Kiryu a go as well. Thanks!

It might be a climate thing. I live right on the edge of 8b/9a, so I don’t have long, temperate periods where moss – even local spores – are likely to thrive on bonsai substrate.

(We get plenty of moss down here, but mostly it grows in shady places – exactly where I don’t want my trees.)

I live in the Mojave Desert in SoCal, with a serious daily wind that is anywhere from 4mph to 20 mph. Summers are 100+ temps and that + wind is just terrible for moss development.

Couple of things I’ve done that have made a WORLD of difference for moss development are the following:

Using 50% shade cloth during the late Spring - Early Fall. Anytime temps were near 90’s regularly I have shade cloth up.

I put up a fence on the south and west portions of my trees to help protect from wind that we get daily from the southwest. It doesn’t stop ALL wind, but it definitely cuts it down significantly.

Lastly, I’ve watered more. This is something most people aren’t comfortable with. I did a whole year the previous year watering maybe morning and night by hand. I had the trees up against a building on the west for late afternoon-ish shade.

I currently have a mix between a drip irrigation and misting system. It waters for 20 minutes at 4am in the morning to significantly drench everything. Extra water runs out anyways. Then it runs again around 11am and 3pm when temperatures are picking up. This isn’t as long of a run, but it keeps the area damp (relative humidity) and rewets the top portion of most of the trees. This is the main key for the trees to keep up with moss IMO. I then water later in the evening by hand with more “ideal” pH water.

This sounds ridiculous like I’m overwatering my trees, but they are all healthily growing for over a year. I change the times to adapt to the season. This isn’t to replace my hand watering, but to keep humidity up and make sure trees are damp incase I wake up late, miss a day etc. I even have several trees in nursery soil (Ginkgo, Ficus, Jap Maples, Oaks, Mugo Pines, Butterfly Bush, Silver Maple, Pyracantha, etc.) and these even handle being watered this much. If I am worried about something I move it towards the end so it doesn’t get hammered with water. Species I have under this system in bonsai soil are as follows for more information (Redwood (evergreen), Chinese Elm, Hawthorne, Pyracantha, Japanese Maple, Silver Maple, Live Oak, Ginkgo, Siberian Elm, Hackberry, Pomegranate (in nursery soil as well), Grapes, can’t think of anything else. I can post pictures if you’re interested in the system.

It has helped grow moss on things I’m not even topdressed as well.

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Also, just now recalling this: isn’t kiryu just the Japanese word for their native lava rock? So isn’t the only advantage of kiryu over black/red lava rock its color?

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Same deal here at 7000’ with low humidity most of the growing season. I just started adding akadama to my volcanic mix and applying the Mirai top dressing this year. Moss (even sphagnum in nooks and crannies) is establishing only on broken down akadama patches. I’m hoping it spreads. Moss “roots” need fine particles. Pick up any patch of moss in the forest and it has super fine organic and mineral particles stuck to it.

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I’ve been using kiryu as my top dressing for the last week and it’s been an amazing help for calibrating my watering.