I always figured it was because bark takes forever to break down, thus supposedly preventing weeds forever. IME, it does a crappy job at weed prevention but YMMV.

It doesn't have to be pine bark - any aged conifer bark (even cedar) will work. Bark mulches in my area tend to be either Douglas fir or western red cedar, since that's what grows here and what the timber industry focuses on. Bark fines/conditioners and/or locally mixed potting soils include bark fines from these species and the soil works perfectly well.

What makes conifer bark fines so attractive as a container soil ingredient when its size is appropriate is it's durability. It contains a high concentration of a lipid called suberin. Suberin helps prevent microorganisms from cleaving hydrocarbon chains and thus breaking soil particles down to soup consistency. Durability is critical with a container media as it affords the consistently fast drainage required while maintaining aeration and porosity. Hardwood barks and the heartwood of most species contain much, much lower amounts of suberin. This virtually guarantees extreme N immobilization and rapid breakdown when the product is used in container soils.

I don't know about suberin content, but in my area, larch bark seems to be the most common. And has a reputation for taking a long time to break down. Added advantage is that it tends to have a nice smell.

Larch is a conifer so no reason it wouldn't be appropriate to use :-)

Pine bark - or other light-weight, slow-decaying stuff - keeps the container mix from packing down. It's a local product, so use what's available instead of shipping in things.

I have a bunch of shredded bamboo stalks. Do you know if that would work too?

I warned about this last year, and, at least in my area, it has now come to pass - Home Despot has stopped carrying any sort of mulch except for shredded rubber and dyed hardwoods in any quantities suitable for those of us who have more than 2 or 3 orchids. I can't even get the Mountain Magic Soil Pep in my area (or anywhere within 100 miles) though it is still in the database so one presumes they must be still carrying it SOMEWHERE.

I have no idea what I'm going to use to replace it. I'm pushing 60 and disabled - plus, HOA - so getting a truckload of it from a local bulk supplier isn't in the cards either.

After considerable experimentation with various versions of gritty mix (since Turface is unobtanium for me there was no chance of using the orthodox version) I had settled on my own concoction, a mix of pine bark, peat moss, and Growstone. The stuff is wonderful. However probably less wonderful in the absence of pine bark fines or nearly-fines (which is basically what the Mountain Magic Soil Pep is).

Lowe's still lists large decorative pine bark mulch but the pieces are ginormous and not suitable for container mix. Also not suitable for little old crippled ladies to be breaking up by hand into smaller pieces, plus that triples or quadruples the cost - since the 2 cu ft large particles break down into much smaller total volume. So not cost effective either.

I'm searching assiduously but have yet to find an affordable solution. Who knew that pine bark soil conditioner/small particle mulch would one day become unobtanium? Apparently I will soon be "testing", much against my will, a mixture of Growstone and peat moss only.

Thank you for the responses everyone!

gardengal,

"Hardwood barks and the heartwood of most species contain much, much lower amounts of suberin. "

what about the heartwood of conifers? the bark of all conifers is a yes....but the heartwood of those?

i ask this because there is a lot of cedar mulch around here and I would love to use this however it doesnt specify that its the bark of cedar

Try it and see is the only real answer. But since the wood is more valuable than the bark, it's more likely to be bark. Now for plain old trivia: the most common 'cedars' in North America are not actually in the cedar family but thuja (cypress family). But that has no bearing on your use.

Only the conifer bark keeps its shape and, thus, soil porosity. Not the heartwood.

tj

"Now for plain old trivia: the most common 'cedars' in North America are not actually in the cedar family but thuja (cypress family)."

It could be argued equally as strongly that most "cedars" in North America are actually junipers :-) Juniperus virginiana = eastern red cedar. Neither assumption is correct as neither are true cedars. In fact, a lot of conifers are called cedars that have little to no relationship with true cedars, Cedrus species. On the west coast, the 'cedar' bark is most likely to be western red cedar, Thuja plicata.

It has been said:

"Only the conifer bark keeps its shape and, thus, soil porosity. Not the heartwood."

Actually that is not the issue. The issue is that as the wood (not bark) breaks down, it robs the soil of nitrogen and has a negative effect on helpful soil flora/fauna. NOTE that when used as mulch there is no issue, its only if you are actually working it into the soil or using it in a container mix. You're fine using the stuff as mulch (as long as it isn't the dyed stuff that is basically ground up houses).

However there has been research done on using aged whole-tree mulch as soil amendment which seems to indicate that if you age it for 1 to 2 years, the nitrogen-robbing effect is greatly reduced, making it "safe", from that perspective, for use as a soil amendment.

When I have to mix new container mix I'll try the cedar stuff with the Growstone and peat moss. At least you can still get the cedar mulch reliably.

Rumors that cedar mulch has "alleopathic" properties (eg it will kill or damage plants) are unfounded according to Linda Chalker-Scott, a soil scientist with considerable research experience with mulches and soils.

"Concern: Woody mulches, such as cedar, leach allelopathic chemicals that kill other plants.

Evidence: Many plant materials contain allelopathic chemicals, which can prevent seeds from germinating or kill young seedlings. Most compounds have no effect upon established plants. Only a few woody materials have been found to contain allelopathic chemicals (e.g. Juglans nigra, black walnut). Cedars (Thuja spp.) have not been found to have this ability."

From: https://puyallup.wsu.edu/wp-content/uploads/sites/403/2015/03/wood-chips.pdf

The article further states that the thujone in shredded cedar seems to repel at least some insects. Maybe soil gnats are among them!

I have hopes yet for shredded cedar mulch.

Peat moss, incidentally, is another thing that has deteriorated these days. The only stuff I can get semi-affordably locally is now the finely ground stuff intended for use as lawn top-dressing. Home Despot and Lows both have stopped carrying anything else. If they still carried pine bark mulch in small sizes (like the Soil Pep) I'd now be looking at reducing peat content in favor of more mulch in my container mixes, but ... hopefully shredded cedar will work out better. It'll be sometime next year or maybe the year after before I can test it.

At least the Growstone lasts for-virtually-ever, LOL! You can rinse old worn out potting mix and sift it out and reuse it. It tends to float up while the organic stuff that has broken down will sink so I float it in 5 gal buckets and scoop it off the top. It is easily sterilized in a 5 gal bucket of bleach-water.

It will break with handling over many years. I'm thinking of giving the larger 2" chunks a try and see how those work out - they will last longer (in the sense of remaining in large enough chunks to be useful) than the smaller stuff. But given that I usually don't need to rework this mix any more often than 3 to 4 years to refresh the bark content, the smaller stuff will probably remain useful for at least 10 years and I suspect longer. I can't tell for sure as I've only been using it for 3 or 4 years so long-term data is not yet available - at least not from me, LOL!