Do Japanese Black Pines prefer terracotta pots?

Most of my trees are young seedlings 2-4 years old. I initially started with a pretty dry mix but after thinking about it some more I decided in such a young age, a dry mix with little organic material is likely counter productive and so this year I’ve made my soil more organic which should provide both more nutrients and hold more water.

In the interest of maximising development in these early stages, I’m curious about the role of the container material; specifically, how do Japanese Black Pines respond to growing inside terracotta pots vs black plastic pots?

I agree it is important to match ones approach with your individual situation and your situation may benefit from a change.
That being said the drier mix has advantages of allowing more frequent watering during early growth stages. If your situation requires higher moisture retention then a bit more organic in the mix may be helpful. I would stay below 5% as a normal guideline. This is based on research for optimal root growth combining air, moisture and nutrients. In the case of inorganic mix then provision of nutrient on a regular basis is required.
The use of terracotta pots will also add higher moisture retention and some cooling insulation qualities absent in plastic pots that may be very beneficial in hotter, drier conditions. Or simply because the watering routine is less frequent!
I have used all the combinations you have suggested and found the best growth pattern in a drier mix with frequent watering and heavy fertilization ( Organic ) I am retired and can water when required, multiple times per day if desired. I also have an automated system for selected grow beds and potted trees.
I keep this routine up for the first six years of development. The only change during this time is containers, Using plastic pots for the first year, colandar in the ground for year two and three, wooden grow boxes for years 3 to 6 and moving those destined for medium to larger designs into anderson flats for final container development. ( beyond six years)
I am currently using terra cotta pots for JWP that i am air layering. ( in this case i wish to have a more moisture retentive environment and not risk any drying out) My normal mix has 20% Akadama, 40% Pumice, 20% granite,20% Lava. Fines removed and same particle size.
I am sure others will contribute their ideas and share different approaches. I am currently propogating, developing and refining JBP,JRP, JWP, and collected Shore Pine with the same process and soil mix!
Containers and fertilization routines change with age and stage of development.


I am somewhat surprised at this statement although I don’t have your experience. I have always assumed that evaporation was the major component of terracotta cooling, leading to lower moisture retention within the pot, as opposed to plastic pots. My experience is with more organic general soil mixes with less frequent watering, so this may be another bonsai soil difference with which to become familiar.

The black plastic heats faster than the thicker terra cottta that also holds moisture in the micropores of the terra cotta.
When you water the same mix in plastic it retains on the basis of the mix only, no absorption by the plastic. When you water the same mix in terracotta , the terra cotta absorbs and retains additional moisture throughout! It is true the cooling effect comes from surface evaporation but the terra cotta pot retains moisture for quite some time beyond the surface exposed. Thus the mix dries out slower as well!
Hope that explains it well enough and i understood your question. I may have worded it poorly. A simple way to check for yourself would be to measure the water retained in both circumstances and check how long it takes for both to dry out in the same circumstances!

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Thank you for that clarification.
I took me a moment to recalibrate my square plastic with the round terracotta. Am I correct in assuming that this test should be based on soil volume?

This is an interesting insight! Could you elaborate on the role of frequent watering in seedling growth? How is this more advantageous over using soils that (within reason) can better retain moisture? Is this todo with sacrificing the available space for oxygen to occupy with soil particles that can hold moisture?

This is based on research for optimal root growth combining air, moisture and nutrients.

Could you refer me to this research please?

I would stay below 5% as a normal guideline.

This is significantly less than the organic material I’ve mixed into in my soil this year. My thought process was when a tree is so young, it’s feasible to let nature take care of the business (with lots of fertiliser help) and let the coarse growth deliver the desired trunk thickness.

The above is in contrast to the practice of switching to an inorganic mix when its time for refinement and needle length reduction. This method relies on precisely controlled applications of fertiliser which can only be effective when the tree is sitting in a mix that’s completely void of any of its own nutrients.

@Riversedgebonsai in your opinion is this not an effective method for maximising early year’s growth?

colandar in the ground for year two and three

Do you take the tree out of the ground to work on the roots between year 2 and 3?

I am currently using terra cotta pots for JWP that i am air layering.

Holy cow, this has to be the topic of my next question :smiley:

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As you can probably guess my comments are based on more than one research article and not a small amount of experience and study!

  1. Frequent watering has the additional benefit of introducing fresh additional oxygen, flushing the media, keeping organic fertilizer on the surface decomposing and mixing into the Bonsai Soil.
  2. Agricultural research shows that the highest quality of soil for root production includes approximately 5% organic matter when ground planting. The mechanics of growth are different within the confines of a pot. Thus the additional flushing is beneficial in a pot. It is easier for excess byproducts and decomposition to escape in the ground. This is also why correct watering technique is so important. Water thoroughly until the water is running clearly out of the bottom holes of the container each time.
  3. Now for your homework i suggest googling articles for optimum root growth conditions.
    Focus on the % of Oxygen, the % of moisture and the temperature range to begin with.
    The next step is to determine the space required for those percentages, what type of particles allow that, what shapes work best , and finally what difference does it make when particle sizes are the same or quite differrent!
    Two articles that explain the above are written by Dr. Scott Alan Barboza. The titles are Introductory Soil Physics, and Inorganic Soil Components Part 1. They are both short articles approximately 18 pages each with references stated and additional reading suggested.
    If you reference crop studies in Agriculture, Horticulture, or Silviculture the results for optimum root growth soil composition will be similar worldwide. The components may vary but the goals remain the same. To create optimum conditions. As Bonsai practitioners we must adapt these results for trees in shallow pots. Very differrent than in the ground or in tall narrow nursery containers.

Yes that is one of the variables that must be calculated. It is simpler if the containers being compared have the same volume and are filled with the identical mix. Then the only variable to measure is the amount of water retained after watering. And the only other variable is the composition of the container, terra cotta versus plastic!
Water retained is obtained by starting with the same volume being poured in each container. Capturing the amount that drains through in each case, measure the amounts and compare the differrences.

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