I planning my first raised bed, and wanted it to be 18 inches deep. Is it best to just put top soil in, or should I do layers? Should rock phosphate be mixed in? Any suggestions for the best soil mix appreciated. The beds will be large so I don't see how I can do the type of soil mix I'm working up for bonsai and Japanese maples. What is practical on a large scale?
What should I put in 18" raised beds for soil mix?
When I start new raised beds, I don't purchase soil, I start filling them lasagna style. First layer is heavy cardboard to smother any weeds or grass that might still be there. From then on I layer paper, hay or straw, leaves, cut grass, manure (i use rabbit) and kitchen scraps. I do this over and over until the bed is over filled as it will settle down. Water each layer as you put it on. Come on over to composting for more information. http://davesgarden.com/community/forums/f/soil/all/
I plant right into the layers, just poke a hole and plant. Some people put a little soil in the hole, I don't bother.
What type of soil/other is below the intended beds?
Soil from mine. You can SEE the tilth.
Al
Cathy4-- Your approach would take some time before it is plantable, I assume one season?
Tapla -- What approach do you use?
I used a mixture of pine bark, reed/sedge peat, composted manure, sand, and Turface. I mixed it well & planted in it immediately. I had some N immobilization the first year that I corrected with an occasional application of MG 30-10-10. I haven't had to use fertilizer in subsequent years. To make up for shrinkage, I simply add pine bark mulch yearly. It breaks down slowly & replaces lost bulk. The soil is home to plenty of life, and I'm very happy with it's productivity. I have 6 4x8 bonsai nursery beds filled with the soil & all the plants I've planted out are doing very well.
Here is a Styrax japonica, planted as a whip thinner than a pencil and lifted as a bonsai start, after 3 growth cycles:
Al
Granite, I load the bed in the fall/winter and plant in the spring. It doesn't look like "soil" but my plants grow great. Tapla is very smart, his way is very good.
Thanks, Cathy. That was really nice of you. I have to say though, I forgot where I was. I'm used to talking to Granite over on the bonsai forum, and that's where I thought I was. Duh!
Al
Al, I'm happy to hear about your bonsai anywhere ;-)
Clearly my main challenge is to find a decent source of fine bark in quantity.