Best way to thicken trunk

So I’ve been growing this Olive and many others for decades (from seed). In the past few years, I moved them from small bonsai pots to large nursery pots to thicken the trunks. Progress seems very slow.

  • Should I let them grow wild with minimal trimming? (I keep pruning the branches)
  • Would these do better in an andersen flat? (does this have to be on the ground or can I keep it on concrete)
  • Should I move to a bonsai mix of Pumice, Lava, and Akadama? (can i use something cheaper?)



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Pumice and some coconut coir allowing roots to grow into the ground seemed to work great for this guy! Great video.

I wonder how large that pine would have been if he grew in premium gardening soil.

Interesting video. The best thickening in the video was when the roots escaped into the ground, but it resulted in something that has to be cut back very hard and redeveloped.

For the olives, I would suggest the Anderson flat on the ground, with a 50/50 mix of organic (I like sieved bark) and aggregate, along with a year or two of free growth. Sliding a shovel under the Anderson flat to cut the escape roots after the 2nd year is apt to be a good idea. On concrete the growth will be less, but the wider pot, organic mix, and free growth will be better than in the smaller pot and a lave-pumice-akadama mix. Remember that we use akadama to scale the roots and refine the branches.


Thanks Marty. I’m challenged with space in my backyard. Not a lot of open ground that gets sun - the sunniest spots are concrete.

For the flats, the 5” walls are what I assume folks use for this stage?

Also, is your reference to aggregate as simple as it sounds - like a construction type aggregate of stone? Or would pumice be better?

I would use pumice, lava, or pearlite, as the aggregate with pumice being the first choice. The combination with bark is basically a nursery mix that keeps a little more structure. The 5" tall 16" wide (13 cm by 40 cm) Anderson flat would be my suggestion. I build similar wood boxes with mesh bottoms for this purpose. I also agree that the olives are going to want lots of sun.


And now on my quest for bulk pumice.

Use the search icon and type pumice. There have been a few threads with links to various suppliers. Some landscaping supply companies have it in bulk, the ones that have various rock, sand, bark, decomposed granite, etc.

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Clearly a series of mirrors is in order :laughing:

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Where I live pumice is fairly non-existent. This is the cheapest source for me. The description is a tad misleading. It’s more like 4gal, but whatever. If you’re on the west coast, especially the PNW, you can find pumice fairly readily…or so I’m told.

It doesn’t sound like you have the space, but putting a tree in a grow bag into the ground works as well. That’s assuming you don’t care about branch development. I use this strat when my goal is purely to grow the trunk. However, with my “field growing” conifer I find that I’m able to at least setup the primary branching structure.