What can further prevent root growth down in a 1-1.5 meter pit?

[brp7]

I was thinking of planting some tropical trees (Cassia fistula, Delonix Regia, Goose berry) in the ground from a big pot. To pull it after a certain growth, would it be a good idea to seal the bottom with some material which can prevent the roots from growing down? If so, what is an ideal material? They are about one and half inches now.

Thanks,
brp7

 

[Lorax7]

Just periodically dig them up, do root work and replant in your grow bed. If developing the nebari is a goal, you can plant each tree on top of a tile to encourage the roots to grow laterally before they go downward. You can’t really stop downward growth. If water can percolate through, roots will get there eventually.

 

[brp7]

Just periodically dig them up, do root work and replant in your grow bed. If developing the nebari is a goal, you can plant each tree on top of a tile to encourage the roots to grow laterally before they go downward. You can’t really stop downward growth. If water can percolate through, roots will get there eventually.

Since these plants are not breaking the bottom of the plastic pots, but rather getting through the drain holes, I believe some plastic would prevent the downward growth and force the root growth sideways.

 

[ShadyStump]

Since these plants are not breaking the bottom of the plastic pots, but rather getting through the drain holes, I believe some plastic would prevent the downward growth and force the root growth sideways.

Anything that will stop water will usually also stop roots.
Plastic sheeting will work, at least for a couple of years. I have seen roots punch holes through it, but it usually takes time for something like that to happen.
A wide hard tile of some sort is ideal, maybe even a paving stone of some sort. I have seen people use wood, but it will rot away after a few seasons years, and may not last longer than a year in some climates. It's more practical in dry climates.

Depending on the tree species, and your soil and climate, place the tile or plastic about one to two hand widths below the soil, and place the tree directly on top. Arrange the roots to spread outward, and fill in the hole. Remember that planting shallower may require you water more frequently, at least until the roots reach the edges of the tile/plastic and start heading downward.
You can got out once or twice a year and dig around the perimeter of the tile to sever roots that are growing out past it. This will encourage more roots in the top of the tile, but again, you will likely have to water and fertilize more.

 

[penumbra]

Sheet copper. It will even stop bamboo roots.

 

[Lorax7]

Since these plants are not breaking the bottom of the plastic pots, but rather getting through the drain holes, I believe some plastic would prevent the downward growth and force the root growth sideways.

Plastic stops water too, though. In order to have drainage, you have to have holes or have a water-permeable material. Roots can go pretty much anywhere where the water can go. Best you can do is delay downward growth a bit by having some non-permeable material below that forces lateral growth to occur first before the roots reach a spot where they can go down. This is what planting on a tile does. Trying to permanently prevent downward growth is not really doable. As Jeff Goldblum said in Jurassic Park, “Life, uh, finds a way.”

 

[Paradox]

sometimes people plant a large tile under the plant, or a paving stone would work too
Just needs to be big enough