For now, I would be careful to rinse the deck after watering every time.

Josh

But I have my pots on plant dollys so there is several inches of AIR beneath the pot.

Has nothing to do with the MGMC, has to do with lack of air circulation.

We know you're a vocal "proponent" of Miracle Grow, and we're happy that you've avoided
the problems that are directly associated with this product.

Josh

Either way different soils are different and a different soil could also stain the same deck.

As MGMC is the same soil being used in two different settings and causing at least one deck to be discolored with another saying the deck isn't discolored by elevating the containers........ could deck stains be different from one deck use to the other to cause the deck discoloring of stain result ?

Magically I have 740+ quarts of it which I water daily and have no such staining of any kind whatsoever.
Been using it for many years with no staining.

I had a couple of pots just sitting flat on the deck prior to getting dolly's and both of them started to darken the deck underneath it in just a few days, I moved the pot and the darkening went away. I was water logging the wood which will start to mold it and stain it permanently from the lack of air circulation.
This is THE leading cause of decks being ruined.

and it has ZERO to do with what ever soil is being used.

But most of this can be alleviated by simply making sure you have plenty of air circulation. The faster the wood dries the less chance there is of any staining.
However if you have a very high tannin hardwood and your water from your hose is high in iron you are probably going to get staining almost no matter what you do.
Unless you seal it with something like WoodGuard which I think is some Tung Oil Bees Wax concoction.

and you need water soluble iron in your potting mix as a nutrient.

We had pretty good results with the Wolman Durastain semi transparent in Natural Cedar color.

Here is our deck after about 11-12 months after staining, still looks pretty good but I am sure will have to be re-stained in another year, none of the deck stains last as long as they say they do and it is better to reapply long before it starts to degrade.

If TSP is handy you could try a small spot to see if scrubbing works TSP could also be a failing effort if I really had to say.

If a nice looking deck is important to you for guest reasons all I can add is we all have guest at one time or another guest come to visit us not our decks most times these types of problems are often overlooked by the BB-Q to the swimming pool and a soft voice explaining what had happened if asked.
A final idea is :

Have a Safe and Happy Forth

MrLike, I apologize for the wording in my original reply - I did not mean that the mix should
be switched this season....because it's already so late in the season. What I meant was that
for next year, a different mix should be selected - a mix such as the 5-1-1 that runs clear
after watering.

Josh

I fully saturate my containers of 5-1-1 the day prior to fertilization,
then I fertigate the following day. That moisture has a good sit in the mix,
and yet when I water there's no tea-colored liquid running out.

Anecdotal evidence isn't the best, but this is what I've observed over the past
three years of full-time 5-1-1 container gardening.

Josh

I guarantee that if you place a pot flat on a deck with no air circulation you WILL get dark staining from mold/mildew, dirt collection that will keep the wood moist longer etc.
Plain and simple and it doesn't matter what kind of wood you have or pot or mix, some may be worse than others but your deck will stain and eventually rot.

The water coming out of my pots certainly isn't "tea" by any means, I have never noticed any tint to it at all really but I have never captured it in a white container to check.
Either way we have zero staining of any kind white or otherwise.

Could also be that our deck dries faster due to it being 20' in the air with plenty of gap between the boards.

I imagine there are numerous variables, but one 100% certain way to stain and rot your deck is putting pots or anything else flat on your deck for months on end.

No need for you to continue in this rude fashion.

Josh

Drum roll please::: what stain other than is being used on the other deck is being stained by container run off Howel ?
With a mix soil of costume type (5-1-1) no run off stains on his deck what stain is Josh using on his deck ?

Nunya: You had them with the pic but you added more than you may of wanted too. Caution on internet guarantees or a word of warning It's peps like me that want you to send the check out first When check is received and bank has cleared then Ill water run off via a container passing it though an elevated catch I say this cause if there is one person who can mess things up and really bust them bubbles.... Well how am I doing ?