Hi Chris, there was a discussion about re-using potting soil: http://forums2.gardenweb.com/forums/load/contain/msg0516433325968.html

HTH!

Here is a link that might be useful: can I 're-use' potting soil?

The link DesertHills provided is a good one. I fall into the category of 'no way am I buying new potting soil every year!"

Just add some compost (bag bought is fine) to 'rejuvenate' what you have. The peat in most potting soils breaks down over time, the compost provides the beneficial organic content, some fertilzer content, especially micro nutrients, and good water retaining/draining properties.

I would suggest that if you are replanting a pot then mix 10-15% compost into the old mix. If you are overwintering a pot then just top off the lost volume in the pot with compost in the spring and you are all set.

I am lazy with containers for annuals (my windowboxes, some other pots). They get old potting soil and MiracleGro. But I do try to give perennials (especially roses) a good shot at establishing themselves. What I do then is to recycle the old soil into another container reserved for annuals and pot up the new plant with new soil.

something that I read recently, but don't know what it means in practical terms is that the peat which makes up the bulk of most commercial potting mixes has a very low ph of 3-5-4.5 or thereabouts. This is unsuitable for growing much of anything so dolomitic lime is added to adjust the ph of the mix toward neutral. Over time the peat breaks down releasing acidity into the mix and the lime is flushed out with repeated waterings.

I would imagine this downward ph drift could be reduced/eliminated by annual additions of compost (near neutral in ph with some buffering ability) or fresh potting soil (which would replenish the lime).

I don't know how long it takes the mix to drop significantly in ph, but this might be something to keep an eye on if plants start showing yellowing or other indicators of nutrient deficiencies despite being fertilized.

Would the "Composted Humus" that HD sells be considered "bag bought" compost? I've purchased some that I'm using in Lasagna beds I'm building but it is very fine textured except for some course round things and a few sticks that I screened out and threw into my compost pile. Thanks, geekgranny

Yes, 'composted humus' would be fine. It is kind of an oxymoronic name because compost is mostly decomposed organic stuff and humus is organic stuff decomposed to the point where it won't break down further under normal conditions.

I think the stuff labelled as composted humus is often just composted wood products. It will work fine. Ultimately compost is compost is compost regardless of what the initial ingredients were.

Thanks username 5. Good news as there are several uses I can find and, as I remember, the price was "okay". geekgranny