You CAN grow in raised beds in soils that have a very high % of OM if you wish, but you should know the downside. A high % of OM often means poor water retention and often poor rewettability. Lots of OM ensures lots of shrinkage, and if the OM you choose doesn't break down very slowly, then N immobilization can present significant issues. In most cases, if your native soil is decent, something like 75-80% native soil or decent topsoil with the remaining fraction being OM in the form of pine/fir/redwood bark fines, finished compost, or a fraction of sphagnum peat. The soil in my raised beds looks like this: You can actually see that it has wonderful tilth. It's about 80% OM (pine bark), extremely productive, and full of soil life. The downside is it shrinks quickly, so the pine bark fraction needs topping off regularly, which I do by mulching. I've also been adding used container soils that have a 2/3 mineral fraction as mulch, which has significantly reduced the shrinkage with no apparent loss of productivity. FWIW - pine bark fines will be considerably less expensive than potting soil, and because it breaks down MUCH more slowly, shrinkage and N immobilization will be much less a problem. You might wish to consider that tack. BTW - you WILL need to add fertilizer - plan on something heavy on the N to compensate for N immobilization, especially in the first year. Mushroom compost is often partially decomposed straw with lots of urea in it. It's often very hot and high in soluble salts, so treat it like fresh manure - probably not a good choice for something in the more immediate. Al

Crystalshoe- Hydrology, not the size of the bed or container, determines whether you're growing in a raised bed (RB) or a container, and by extension, what type of soil you can/should use. A planting of daisies in a plastic or clay pot resting on your deck or patio is a container planting. Bury that pot an inch or two into the ground so there is continuity between the medium in the pot and the soil the pot is partially buried in, and it becomes a RB - no matter what size the pot is. The difference is, the earth will act as a giant wick, and remove water that would normally perch in a conventional container planting, but water movement within the partially buried container would closely mimic water movement in the earth or in the soil below. There is a caveat, however. The area where the pot is buried or partially buried would need to drain properly for things to work. If you were to bury the pot in clay soil that allowed essentially no percolation, the pot would simply fill up with water at every rainfall or irrigating. If you're building a RB over a clay soil that drains poorly - don't amend the clay unless you can drain the area. If you do, water will percolate or run into the area you amended, leaving it saturated for extended periods (the bathtub effect). You can remedy this problem if you are able to cut trenches or use a French drain cut into the clay to drain excess water to a lower area away from where you're growing. Not amending the clay below your beds also allows any excess water in the RB soil to move laterally over the surface of the clay where it can evaporate. If you amend, the water won't move laterally until the amended depression is entirely saturated with water. No matter how you look at it, you're eventually going to have problems with a RB over clay unless you can figure a way to use gravity or a pump to move water from the area. As soil life moves through the clay and increases the OM content of the clay below the RBs, that soil will become more porous than the surrounding clay. The pores will quickly fill with water when it rains or when you irrigate unless you have a plan to remove the water. The end game is, the water that collects below your RBs has to have a place to go. It has to drain naturally in a reasonable time, or be directed downhill or to a sump where it can be mechanically removed. Amending the soil beneath RBs just forces you to face the brunt of the problem sooner (in heavy clay soils). BTW - you don't need to use a highly aerated soil like that you referred to in your OP in RBs. In fact, the highly aerated soils that perform so well in containers are probably not a particularly good choice for RBs because they have a steep water retention curve that will have you watering more than you'd prefer. Keep in mind that the time you spend now, properly preparing, will save a lot of time and frustration later. How many beds? Size/depth? Budget constraints high, low, medium? Ready access to materials you think might work? Al

I was thinking of building it now, and just dumping in the partially composted stuff already in my compost bin. This would free up the bin to start filling again with my most recent scraps and other materials. Even simpler ... dump the old plants and whatever is in the compost bins into the new raised bed, along with whatever else you can scrounge. Cover with some dirt, and mix it in the spring.

It is not "wee critters that munch on the wood" that causes the problem - it is how well the wood will hold up to soil moisture. Wood exposed to water rots, some woods faster than others. Douglas fir is not all that long lived when in contact with moisture....only 3-6 years. Pine ditto. But cedars (western red cedar, Alaska cedar, incense cedar and eastern red cedar) are very rot resistant, as is redwood, black walnut, white oak and eucalyptus - anywhere from 10-25 years. Treated doug fir is also good (up to 30 years) but untreated, not at all. And a liner can extend the life of raised bed wood just by virtue of keeping wet soil from direct contact. As to soil appropriate to a raised bed, garden soil enriched with some compost works perfectly fine - you don't need to get overly creative in the mix. A raised bed is just an elevated garden bed, nothing more. If you do not have sufficient soil available to fill your beds, bagged garden soil or bulk 'garden mix' will work perfectly well although I'd want to add some OM if none included in the mix. Raised beds sometimes have solid bottoms and are sometimes located on solid surfaces like driveways or patios but open to the ground on the bottom is most desirable, especially for good drainage. So no rock or stone base. This also allows deeper rooted plants to penetrate down into the indigenous soil as well. Decent drainage is usually a given, just based on the bed's elevation. The "standard" configuration for a raised bed is one that is 8' long by 4' wide. This allows the gardener to access all the plants easily by reach alone without actually entering the bed itself. Height is your choice - if you are growing deeper rooting plants, you might want a deeper bed - but anywhere from 8-16" is about ideal. Obviously the deep the bed, the more soil required. Watering can be done with a soaker hose, drip, by hand or with a sprinkler - it really doesn't matter as long as the plants receive adequate moisture as needed.