Late summer nursery root ball reduction to stimulate root ramification?

[KennedyMarx]

I was thinking about this earlier but haven't seen any discussion about it. The roots react to pruning by ramifying like the foliage, correct? So I am wondering if I can cut the bottom 1/3 or so of a rootball clean off a nursery plant and srick it back into it's container (which will be cut down appropriately). Has anyone done this? I figure it's probably variable depending on species and amount of roots. The point is that I think I'll be able to forced the rootball to get more dense before the spring repotting into a smaller container. I'm thinking about doing this to a boxwood and a couple privets. Any other stock I stumble across in the next few weeks will be considered as well.

 

[Neli]

I was thinking about this earlier but haven't seen any discussion about it. The roots react to pruning by ramifying like the foliage, correct? So I am wondering if I can cut the bottom 1/3 or so of a rootball clean off a nursery plant and srick it back into it's container (which will be cut down appropriately). Has anyone done this? I figure it's probably variable depending on species and amount of roots. The point is that I think I'll be able to forced the rootball to get more dense before the spring repotting into a smaller container. I'm thinking about doing this to a boxwood and a couple privets. Any other stock I stumble across in the next few weeks will be considered as well.

I do that on tropicals all year round...but here climate is moderate all year round.
That is actually a repot with root reduction. Any particular reason you want to do it in autumn?
InJapan we used to repot small shimpakus...shohin and less in autumn...but large ones in spring, and even in spring the small ones were repotted like a month before the big ones...
I do this to all my trees starting with them in the ground.
I would dig gently around the nebari on one side and cut off the first big root I find 1-2 cm from the trunk...depending on the size of the tree. It takes 2 month roots to emerge from the cut point so depending on the variety I would do the same every 2-3 month to the rest of the roots. I dont bother with the lower roots since they will be cut. Just note that my trees in the ground are watered frequent but shallow wateringns, which promote very dense fine roots mostly at the surface... If my trees are in training pots I prefer to cut or strangle roots with wire during repot.

 

[sorce]

I think you would be better off reducing them as much as needed in spring.

Cutting off the bottom is going to give you new downward growth which will also have to be cut in spring. Better to save them the energy now.

Sorce

 

[Txhorticulture]

Contrarian advice

I don't know a whole lot about those species, but.... Late summer could be a good time to do it. You are right that cutting a root is like cutting a branch, it divides. Now would be a good time to make roots divide (as long as it doesn't kill the plant, or make it to weak for winter) i say its a good time because for temperate plants at least, about 80 percent of root elongation occurs in fall.

So you force division now when worst of summer over, roots divide, start to elongate as fall approaches and next spring your plant starts with a better root system.

As an experiment I just cut the tap root off of a bald cypress first year seedling (about 18 inches tall) and potted it in a gravelly bark mix in net pots. I read a university study online that said root pruning up to 70 percent of root system actually produces a larger tree year two. (It forced top AND bottom growth - which seems counter intuitive to me) We will see, the tap root was connected to about 2/3 of root system.

Now this paper was about Taxodium in Florida so use with caution.