Posts tagged “slab

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.