I have built some raised beds 450mm high. I have a plentiful supply of well rotted horse manure with no straw or wood chip. Would it be wise to fill my beds with this or should I add some topsoil?
That is deep beds and if you fill them with organic matter only, such as compost/manure, the level will sink within a year to three quarters or less, depending how much you squash it in (I would walk on top). So I would look to fill halfway with soil, then compost t/manure on top.