Any organic material you can get and which you like the look of. Not gravel.

I would be cautious with that river stone for the bottom, unless you really need water retention. As for mulch I would ho with what is easy to work with. Like wood chips?

If you're going to buy, get plain shredded hardwood, without any paint added or other stuff like that. It doesn't need a brand name. I used to live by a place called "Mr. Much." If there are any nearby, I would look for mulch at a place like that, not @ a store. Apply mulch around plants, but not touching them.

I would also skip the river gravel. There's nothing to be gained by purposely adding rocks under the soil surface.

chunk size is aesthetic.. but also durability ...

bigger pieces take longer to break down to compost ... on the ground i used to use giant cedar chunks.. that would last many years ...

but i would fear that huge chunks will look out of proportion in a raised bed ...

that the variables.. i dont know what you might prefer ...

whatever you do.. dont use chocolate hulls.. if they still sell that stuff ...

ken

i would also agree to STAY AWAY FROM ROCK OR STONE...

I am going to put light colored 3/4" river stone UNDER the cedar raised beds so they don't rest right on the ground, and between those beds to keep the weeds from growing there. I am going to use a matching pea-sized gravel as a mulch for the front yard beds, but shredded bark stuff (yes, we have a Mr. Mulch around here) in the 55' rose bed alongside the picket fence and in the cedar beds.

Why do you not want the beds to rest on the ground? Are you saying they have floors and are not open at the base? If that is the case they need to be treated as containers rather than beds. As ever some pictures would help people visualise your set up.

Between the beds gravel is just a path, which is fine, but it won’t prevent weeds from growing.

As a mulch gravel will not contribute anything to the structure of your soil or nutrition of your plants and it will gradually sink and get mixed into the soil.

The cedar beds have 1/4" hardware cloth attached to the open bottoms to prevent voles and such from digging upwards to eat the roots of plants. My yard soil is pure clay; having the beds rest on gravel will help drainage. There will be weed control fabric between the beds, under the gravel between the beds to keep weeds from growing there. I am not using gravel to mulch the cedar beds, only the front yard garden beds, which are directly in the ground. I don't want wood mulch in those because I don't want to attract termites near the house. Termites have been known to be a problem here. That front yard garden bed soil has already been amended with leaf compost and top soil added.

I've never had a good experience with gravel in the yard. My large air conditioner unit sits on a bed of gravel--The gravel always seems to get into the nearby flower beds. Weeds grow in the gravel. My experiences with gravel have been poor. I wanted to make some garden paths and put gravel on them but after one try we stopped since the gravel really needed some type of metal edging to be dug into the ground to contain the gravel. That's simply too expensive for us. We tried the plastic black edging but didn't stay put. I finally decided to do it right I would need a professional to do it--that's not going to happen.

Raised beds (bottomless) can be constructed on any surface, including clay, brick, asphalt or concrete. By nature they will always have decent drainage without any need for rocks or gravel at the base.

I am installing steel edging to keep the 3/4"-1" diameter gravel where it belongs. I also put weed control fabric under the gravel.

NEVER use FABRIC under anything ... its against Gods rules ... its against nature ...

if its already there.. with stone on top ... oh well ... i cant imagine you moving all the stone now ...

most weed seed is airborne.. ergo.. 2 minutes after yu put fabric down.. seed is blowing on top.... and once rooted.. w3ill grow down thru the fabric.. and you cant pull the darn things out ...

ken

Ken and his absolutes!! 😖 Actually, underlaying a rock or gravel pathway is one of the very few situations where you should use a landscape fabric. It keeps the gravel from becoming embedded in the underlying soil and the path from becoming uneven or with potholes and even muddy in the rainy season. The one thing you are trying to avoid using gravel. Yes, you may get a few weeds but nothing like what you would get without the fabric.