[SallyintNorth]

We have had to install a sewage treatment plant to comply with new legislation.  The pumps make a humming noise constantly, which we want to dampen.  Sandbags on the housing help a lot but we thought it would be good to also plant hedging.

Anyone got any recommendations (preferably backed up by experience of noise reduction!) for native, non-toxic hedge plants?  We don't want the hedge to grow too high as several of us enjoy the view across that area.  Probably will aim to keep it to 3' or so.

We currently plan to have ducks, chickens and geese only in that area, but it's possible we might bring sheep in to graze at times if we need to, and there is always the chance of a cow or pony escaping into that area, so the hedging plants had best be non-toxic to livestock.

[Fleecewife]

Unless your humming is at below-ground level, then a three foot hedge will never be tall enough - it would need to block the ear-to-noise line, so min five feet six to six feet, depending on how close it is to the source.
All I can think of is to put up a fence, the kind with vertical staggered slats that are used at the edge of motorways, close to the sewage plant, then cover it with whatever hedge plants you like, including wild clematis and wild roses. That would hide the fence and give you something nice to look at.

[SallyintNorth]

The pumps are pretty much at ground level.  The housing lids are at about 9" above the ground.  We had thought a hedge right next to them. 

The field slopes down away from our village.  The homes most affected are the ones at the head of the field, and me and my one neighbour, who are beyond those, at that end of the village.  Yes a 3' hedge may not completely fill the line-of-sight to our upper floors, but because of the sloping ground, we hope it should help a lot at ground level, at least.

[doganjo]

I lived next to the Stirling-Alloa-Kincardine line and they started putting heavy noisy coal trucks through at night.  After a lot of complaining to Network Rail, they installed a reflective wooden fence to reflect the noise away from my house.  It was 10 feet high so it was above the height of the trains.  It worked perfectly - took the noise level down for 75DBa to about 35/40 DBa which was acceptable in law.
They installed an absorbent fence only 7feet high in my front garden as there were houses opposite, but it was far less effective - on both sides.  However, the people in one of those houses bought my house when I wanted to move up here, so we are both happy