conifers

Not poisonous exactly, but it's far better to compost them down first.

We use them to top up our bark paths but otherwise, like Spritzhenry says compost them first.

Thankyou for your feedback, to expand on the question , a long row of 50ft conifers were reduced by half and the cuttings chipped around the base of the conifers which was in places 7ins deep , although this has made a good ground covering the landowner is worried it may affect the remaining conifers ?

You are meant to let chippings stand/compost for 4-6 months before using them as the process removes nitrogen from the soil. This was the advice i was given from the RHS when i reduced a beech hedge and various overgrown shrubs.

I think it may slow them up a bit but not do any lasting damage.

Here in southern US we use pine needles to mulch around acid loving plants. I'm guessing that as they break down your clippings will also add acid to the soil in a similar fashion. As long as you don't use them on something acid sensitive you should be okay. A lot of them over time will change the Ph of the soil. So as other members have said composting with other materials will help to avoid this.

Grassroots a 7" depth of chipped conifers is possibly a little deep - I remove about half of and compost first.