United Kingdom

I have a tree question which I'd much welcome any intell you may have to share with me.
I have a splendid middle-aged multi-stemmed laburnum waterei vossii (circa 15 stems)
I've planted 3 more young-ones alongside it to form a kind of walkway.
As-is these new ones are single stemmed, 2 year old trees. I planted them last winter, they've done well so far. Wondering how I can now transform them to multi-stem. My sense is I should harden my heart & cut them down to 6 inches high right now. Would you concur?

Thank you in advance for any thoughts.

• 3 Jan, 2017