I've found that it depends on the size of the container. My smaller balcony-railing boxes (6" deep, 24" long) and the smaller pots tend to be more vulnerable to contamination, so I try to clean them thoroughly and fill them with new potting soil mix every year. The deeper pots seem to be okay if I mix half and half (or so) old and new (if they weren't buggy the previous year). One of our neighbours on the ground floor likes having our old soil to mix in his back yard garden, so it gets a second life!

It's pine bark, but it's hard to say by the picture if the size of the bark is appropriate. It looks like it's quite large. If you read the link Jodi left for you upthread, you probably realize that particle size and distribution is very important to how a container soil performs. Here is something I wrote to illustrate the importance of particle size/distribution: Obviously, I think the grower's soil choice when establishing a planting for the long term is the most important decision he/she will make. There is no question that the roots are the heart of the plant, and plant vitality is inextricably linked in a hard lock-up with root vitality. In order to get the best from your plants, you absolutely must have happy roots. If you start with a water-retentive medium, you cannot improve it's aeration or drainage characteristics by adding larger particulates. Sand, perlite, Turface, calcined DE ...... none of them will work. To visualize why sand and perlite can't change drainage/aeration, think of how well a pot full of BBs would drain (perlite), then think of how poorly a pot full of pudding would drain (bagged soil). Even mixing the pudding and perlite/BBs together 1:1 in a third pot yields a mix that retains the drainage characteristics and PWT height of the pudding. It's only after the perlite become the largest fraction of the mix (60-75%) that drainage & PWT height begins to improve. At that point, you're growing in perlite amended with a little potting soil. You cannot add coarse material to fine material and improve drainage or the ht of the PWT. Use the same example as above & replace the pudding with play sand or peat moss - same results. The benefit in adding perlite to heavy soils doesn't come from the fact that they drain better. The fine peat or pudding particles simply 'fill in' around the perlite, so drainage & the ht of the PWT remains the same. All perlite does in heavy soils is occupy space that would otherwise be full of water. Perlite simply reduces the amount of water a soil is capable of holding because it is not internally porous. IOW - all it does is take up space. If you want to profit from a soil that offers superior drainage and aeration, you need to build it into the soil from the start, by ensuring that the soil is primarily comprised of particles much larger than those in peat/compost/coir, which is why the recipes I suggest as starting points all direct readers to START with the foremost fraction of the soil being large particles, to ensure excellent aeration. From there, if you choose, you can add an appropriate volume of finer particles to increase water retention. You do not have that option with a soil that is already extremely water-retentive right out of the bag. I fully understand that many are happy with the results they get when using commercially prepared soils, and I'm not trying to get anyone to change anything. My intent is to make sure that those who are having trouble with issues related to soil, understand why the issues occur, that there are options, and what they are. Many use their current potting soils (like MG or used soils as a smaller fraction of a new media they put together specifically to improve drainage & aeration, so yes - you CAN use some of the soil you have as a fraction of a new soil, but keep in mind that you aren't going to rid yourself of the drainage/aeration and high PWT issues problems unless your soil is weighted heavily toward larger particles than your current soil is currently comprised of. When you add a little extra perlite and/or pine bark to a peat-based soil, you don't change the drainage characteristics, the height of the PWT, or aeration. You DO decrease the total volume of water the soil CAN hold, and that IS a plus, but that's about all you really accomplish. Add a LOT of (appropriate size) bark and perlite = job done. The physics of how water behaves in container soils doesn't change because someone might assure you it does. As surely as the cow is barred from jumping over the moon by the law of gravity, soils are bound by physical laws to exhibit rather specific and predictable characteristics based on their particle size and distribution (enter the pudding analogy into evidence). If you choose not to go with a soil that has a considerable fraction of larger particles, there are ways to help you deal with excess water retention when it occurs. There is a lot of good information about dealing with water retention if you follow the embedded link. When you get to where you're deciding about how you want to proceed with your soil, we can talk more specifically about tailoring a plan that best supports your methodology. Take care. Al

Unless your tumbler is larger than any I've ever seen, I don't think so. You can check in the Soil, Compost & Mulch forum, but my understanding is that you need to have a hot compost pile of about 3-feet by 3-feet by 3-feet to kill diseases and weed seeds. That is a cubic yard, or 27 cubic feet, or about 200 gallons. Most of the premade composters people buy are too small to heat up enough. They do work as cold composters, but that can take 6-12 months or more, and it doesn't kill diseases or weeds. I have a Compost Wizard tumbler that I use to make my soil mixes. It works great for that. But I am not strong enough to handle more than about 25 gallons of mix at a time. I do cold composting in one of those black plastic bins. I never add left over solanaceous plants or diseased material to it. I use mostly shredded fall leaves, disease free spent plants and left over 5-1-1 in it. It takes about a year to get decent compost from it. Here is a link that might be useful: Soil, compost & mulch forum

I have reused old potting mix - I mix it 50/50 with new. Sometimes I solar sterilized it and sometimes I didn't. But given yours has been dumped in the compost bin already I wouldn't suggest digging it back out. I would worry about it picking up fungi, insects, molds, etc. I wouldn't want to use that in a potting mix without solar sterilizing it, and by the time its warm enough to do that again you'll probably have most stuff potted up anyway. It is a risk - one that I have gotten away with on and off for decades, but still a risk - for ending up with disease or other pests in your new planting even BEFORE your old mix was introduced to your compost heap. Solar sterilization is too much work for me these days so I just don't do it any more. If it were me I would just start maintaining the compost heap (turning, testing temp, etc) and get that puppy working. I would not try to use the potting medium that was dumped in there in a container again. But potting mix you make yourself is MUCH cheaper than the bagged stuff. Miracle Gro in particular is mostly peat anyway, plus the last bag I (accidentally) bought had bigger chunks and sticks in it than I usually see in bales of peat moss. I don't hate it the way some folks hereabouts do - but I do think its generally overpriced for what it is. It (and its brethren) sure is convenient though. The 5:1:1 (pine fines/peat/coarse perlite) bandied about this forum a lot has lots of anecdotal evidence behind it. Lots of people use it. I haven't, but I've no real objection to it except for the perlite component (which I could cheerfully replace with pumice anyway) - its just that its been hard for me to find something suitable AND affordable in the way of bark, and all that screening is a lot of work. I may have found something I can use now for the bark component, but it took me years to home in on the right stuff and I'm not even sure it IS the right stuff yet. It used to be pretty common and easy to find graded pine or fir bark but so much of the "mulch" now is dyed, ground up old houses and pallets, it's gotten harder and harder to find. But anyway. 5:1:1 is what I'd suggest if you can find the ingredients. Home Despot carries a coarse grade of perlite bagged by Thermorock but it seems to be variable and will probably need to be screened and washed. You may lose a lot in the process, you may not. If you can find horticultural grade coarse vermiculite from a nursery, it MIGHT (or might not) be cleaner and more consistent in size. At a real nursery they should be using it themselves in their own greenhouses - in which case they should have an open bag sitting somewhere that you could examine if you asked nicely. Can't do that at Home Despot. That said, basically almost any mix will likely work out OK for your purposes(one season use) that includes 2 or 3 from the following list: Peat (make sure its damp all the way through...