At what stage to shape a box hedge to create a par terre

Hello. I would be grateful for some advice please. Being very interested in the historical background to garden design, I am creating a parterre using box plants. They have been in position now approximately three years but vary in height and depth. Some have reached the height of 35 cm (14") required, others are straggling behind.  I know patience is required to attempt such a scheme and but I`m wanting to try and achieve some semblance of the geometric framework as soon as possible. At what stage should  I attempt to trim and shape the plants into the formal hedges?

I planted a box hedge around 2 and a half sides of a rectangular rose bed a few years ago.  The other edges were trellis for climbing roses.  

I waited till the box plants were all about 30cms high before giving them their first trim taking just a bit off top and sides to encourage them to thicken up evenly.   I've repeated this each year, letting them get a bit bigger each year.   They have now all caught up with each other and are kept trimmed to about 50cms high which is what I need to give protection to the roses in winter.

The usual mantra is to trim box on Derby Day which gives new growth time to harden up before winter frosts but I've done it as late as July with no bother and I do get hard winters.  

Mine get pelleted chicken manure scattered about in spring to feed them.

Many thanks for your response, I found your advice very useful.

Am just about to separte my back garden into three sections using  box hedging to separate the kitchen garden and patio areas.  Please could anyone advise the optimum spacing for nine inch high plants.  Many thanks.

Barbie2 - glad to be of help.

Lorraine - Mine are planted 9 inches apart.  It's an easy distance for me - the span from thumb tip to little finger tip and also the length of my trowel.

In the case of Buxus, the general rule of thumb for plants up to 10" high is to work on 3 plants to the meter which would generally give you a spacing of approx 330mm between each plant, which is about a spade head apart. This however does depend on the finish or final result you want to achieve.

Rui - thank you for your prompt response and excellent advice.  I shall have to be patient it seems to create a formal low hedge over a number of years with clipping only in June, I believe.

i clip  mine in june and did them last week.. never leave later or they get frost damage.. always do them now.. never lost one.. thou my one cone shaped one has been planted 3 years and i thought it about time it had a haircut.... did rahter well with the shaping from eye only.. when it stops raining will take a piccie and add it.