Mix it with the compost or coir to avoid the hydrophobic problem.

I routinely dump old, depleted potting soil into planting beds. And with some 60+ containers, I can generate quite a bit of the stuff over the years!! I am certainly not going to throw it away and I believe it does add some value with aeration to existing garden soil. I too do not use it as mulch but rather mix it into the soil, mostly into a series of raised beds that could use the additional volume.

How old is old? I usually have a leftover bag or half-bag from the previous year. I use it to sprinkle over seed beds I've just sown (flower seeds). Never knew about the hydrophobic problem, so far I haven't noticed any problems used in this way; but good to know why it's not a good idea to pot up plants with it. In fact I bought a new bag last week, forgetting I had a full one left from last year. :( I did use the new one for my urns.

I think the other comments referred to potting soil that had been already used in pots for at least a season and was breaking down.

I do as NHBabs suggests and just mix it with compost or sometimes just dump in compost bin - same thing but a bit longer.

Yea, I wouldn't use it as mulch - it's going to dry out and prevent water penetration to underlying soil.

Unused straight potting soil isn't going to go bad - there's really nothing in it besides peat and perlite, maybe vermiculite, depending on the mix. I do not like 100% potting mix for pots - dries out way too fast. Way, way too fast. I mix it at about 50:50 with good quality top soil. Have been doing this for as long as I can remember, and my plants thrive in pots (no, they don't get water-logged as some have suggested in the past). Because there's soil mixed in, I don't find a need to replenish yearly - I do have to add to it, since the roots take a lot of the mix with them when I clean out the pots in the fall, but I just add what I need the following season, add some timed-release fertilizer (I like Osmocote) at planting time, and I'm good to go.

I dump it under my bamboo hedge. I wouldn't worry about it doing anything except improving the rooting environment for plants, just like any other mostly organic material that falls on the soil. I would not however mix it in, or would I expect it to function as a weed suppressant. In fact if anything it might provide a place for certain weeds that like highly organic soils to get started.

I buy bags of potting soil from an Amish nursery, they create their own mix and sell it in plastic bags. It's what they use in their hanging baskets and planters which they sell.

Well, I used the potting soil from last year. I mixed it with an equal amount of fresh potting soil and coir. I will let you know how it goes. Thanks for all the advice.