A planter box with a bottom is essentially just a large container and as such, should only be filled with a proper container or potting media. And although you can mulch, it is seldom necessary in any container gardening situation and depending on the mulch used, it can alter or impede the fast drainage these plating situations require.

I routinely mulch with compost - it is my preferred choice of mulches. But I only mulch inground garden beds, never containers. I do not want anything to impede fast drainage nor contribute to a decline in aeration.....compost can do both in a container setting.

Ditto. To mulch with compost apply it as you would any other mulch. But on inground beds.

first.. you left out how much of each.. you give us a number.. but not of what.. pounds.. quarts.. gallons.. etc ... i cant figure out a ratio ...

compost that stinks is UNFINISHED COMPOST ...i quit using the FREE local stuff.. becasue it usually isnt a finished product .. not to mention all the glass.. cigarette butts and all the other garbage in it ...

next ... a proper media is a water management system ... retaining what water the plants you are growing need... and draining excess away ... your goo isnt draining ... water moving thru it ....

you can not just throw things together.. and hope it all works out.. you need an engineered product .. you can make it yourself.. but you need to get the recipe from someone who thru experience engineered it.. just wait of al .. hes on his way .. lol ...

the pooling water you put on top.. probably has nothing to do with the compost.. its the stuff that is under.. that is not engineered to allow water to move thru the mess and drain out the bottom ...

i seem to recall complaints about the Kellogg stuff.. but you will have to google that.. or wait for someone else to tell you want problems there may be ...

dont know where you are.. but the easy answer is go buy some promix bx and live your dream ... or try al's stuff ... either way.. i would start over ... and buy a gaint bale.. it stores.. dry.. forever .. i have a giant plastic garbage can in my barn ... its good for houseplants also ...

and throw all this in a compost pile .. add more of the free compost.. turn it once a month.. and by fall you can use it as a top coating in your other gardens ... it would be called a soil amendment ...

as an aside .. mulch is a top coating.. to cool soil .. and reduce weed germination .. it it does over the years break down to a compost ..

a compost it a soil amendment .. that works to build a good soil ... though it can be used as a mulch ... it really isnt..

when you understand the difference between the two word.. you will be further along in understanding how each works.. and perhaps understanding some of the stuff you read online ... and if they are using the words interchangeably.. then find a better source ...

ken

https://duckduckgo.com/?q=promix+bx+lowes&t=ffcm&ia=web

Compost IS a mulch and many of us use it as such...just not in containers.

tj

tj, thanks for pointing that out :-) Many people do not realize that mulching is a process - not a product ! There is no specific single item that is considered 'mulch'. Mulch is anything that is applied to the top layer of soil to help hold in moisture, even out soil temps and deter weeds. It could be rocks, bark, wood chips, grass clippings, pine straw, compost, aged manure, leaves, shredded paper, carpeting or any of another dozen or so items.

Ken, my measurements are in inches. I guess "in" is confusing since it can also be the preposition :) So I filled up with 7.5 + 5.5 + 1.5 = 14.5 inches, 2 inches from the top of the container.

Gardengal, the container is roughly 2x4 feet so it's bigger than your average pot, and thus some people in another forum advised me to use raised bed mix (or even just regular soil). I wanted to use some Miracle Gro because of the built in fertilizer - I want to make life a little easier here and there :) And since I could get the compost for free and I read about using it as mulch, I thought I'd give it a try. If you really think I shouldn't be mulching a 2x4 area, do you think it makes more sense to mix in the compost at a deeper layer? (I got a LOT left, and just built two new 2x4 boxes that need to be filled)

They are raised beds when they are on the ground which has a different dynamic. Lifted up they are a container and they need a container mix.

tj

I'd amend tj's comment just a bit :-) If the planter has a solid bottom - elevated or not - then it should be treated as a container regardless of its size. In which case, I would neither incorporate any compost into the soil mix, nor would I use it to mulch.

As @gardengal48 (PNW Z8/9) said, you have created a raised bed soil in a self-contained (giant) pot. That could still work, but it will be heavy and not be the best draining medium.

But it's there so let's assume you are going to go with it. The next issue is that you have not mixed the ingredients together, but seem to have layered them (correct me if I am misunderstanding). The roots need all of that together, not stratified into individual layers. You will improve things if you take out any plants that are there and mix the layers up so you have an even blend of all your soils.

Finally, while compost can be used as mulch, that is not it's strongest role in the garden. Just meaning that there are other substances that do a much better job of letting water through, keeping the roots cool, moisture in, and the weeds out. Shredded bark, which you can either buy at a big box store or get free from anyone that does tree trimming or cleans up yard waste, is a much better (and cheaper) mulch. Another sometimes free option is shredded autumn leaves. Bonus: after a couple of years, these turn into compost and improves the soil without you having to lift a finger (other than replace it with a new layer of mulch).

What makes a "better" mulch is I think merely a matter of opinion :-) I find compost excels at ALL the things mulch is supposed to do. Plus, I prefer the appearance and the nutrient content. Whether shredded bark or wood chips is a "much better" (and cheaper) mulch could be up for some debate :-) Can't get much cheaper than homemade compost!!