Use heavy cardboard as a weed barrier--does a good job and the worms love it. Then, toss in what you have as in compost bin.

As for soil, do be careful if you buy--some I used set up like concrete and it took several years of serious cover cropping to get it even reasonable.

16" sounds excellent--mine are 12" and wish they were higher to sit on the edge rather than kneel & reach.

I just finished filling the first raised bed, 4'x9'x16", with 1/3 topsoil(good stuff),1/3 pine bark fines, and 1/3 compost.
That was a lot of material for one bed and a lot of work mixing it. Getting a late start for the fall/winter planting but better late than never!!

I used the following mix in equal parts (20% each):

Horse Manure
Leaf Compost
Peat
Vermiculite (coarse)
Com-til

Amazing mix. Grew everything!

I dig in a mix of peat and horse manure annually. My supplier throws in some chicken manure too sometimes.

I am currently at 12 inches; thinking of moving up to 18 this year.

I am going to build my raised beds higher this year for several reasons.

One is because the soil level in my beds is rising due to sheet composting and mulch. Two, because I am getting older. Three because my back hurts.

I built Ours 24" high and 5X10 and 4X8 love em. I put a 2X8 on top for a seat and you can sit and do what you need to as well as makes for a very comfortable height.. 1 time expense and really worth it.

Mark

But does it keep roots out? And for how long? Mine are about six years old and 12 riches deep, and the redwoods are winning. Overtime I think I can beat them, I look up at them, and realize it is futile.

If the problem is tree roots, they'll follow the water and nutrients right up into the bed. I have a couple of beds I have to dig deep every year to get my neighbor's tree roots out. I dig a trough along one side of the garden and cut them off, and then pull out the big ones - a real pain. Every spring when I start planting, the roots are always back.

If you are building a large raised garden, I would suggest the following: 1. use uncolored cardboard or a double layer of black and white newspaper as your bottom layer (root barrier) (worms love it), 2. Visit your local transfer center (if they provide free composted leaves) and put a 6 to 8 inch layer of leaves on top of the root barrier, 3. Fill the remainder with a mix 1/2 compost and 1/2 top soil or garden soil.

The tree roots can travel up into the bed easily. My compost bin is just a 4x4 fenced in "pile" and tree roots usually move up into the bottom foot or so every year. Thats after I put down several layers of cardboard in the spring. You might want to put down a fine meshed screen at the bottom of those puppies. Cardboard wont keep them down long. Its good for weed suppression, but not tree roots!

We are making keyhole gardens. We've done 2 so far. I'm tired of bending over so we are changing methods. We are also setting up a large hydroponic bed. No more bending over.

Hilary49: What is a key hole garden?