Getting a good soil mix for large planters
I have built some extra large planters, which are built into a deck frame i've built. Ive taken the inspiration from terrace gardens where they will build a large planter to add interest to the side of the decking.
I have one large planter at the moment complete, its 3m long, 60cm deep and about 50cm wide, so its a good sized planter. Its been plenty reinforced, and to the sides, a 1200gauge poly sheet has been added to retain the ingretity of the bed, and also to protect the wood. The sheeting only protects the sides and laps at the bottom however, it is open to clay at the base in case of any root development or drainage needed.
So far, i've had some old pea gravel hanging about, so i've filled the bottom of the planter about 10-15cm deep which should aid drainage but I'm now looking at what to put in it, so that come next year when it is filled with plants it'll be well fertilised soil.
My thoughts are to buy a load of well rotted manure and pile it in, perhaps with topsoil. I have loads of clay soils which I've dug out of the garden, so wondered if I could pile that in with the manure to break it all down into good soil? Just another way to avoid wasting the heavy clay soils and to avoid having to replace it with topsoil? That may or may not be a good idea if it wont break down the heavy clay. I also have some sharp sand but understand that you need a pile of it to make a difference in heavy clay.