How it looks from my perspective: If the decision to reuse container soils is an economic one, who can disagree with the decision? If you aren't concerned about expense and are willing to go to some minimal extra effort to build a good soil, that is what I would elect to do. Here's why: Container gardeners need to direct primary focus to insuring that the soil they are using will remain able to provide adequate air to roots for the expected life of the planting. Along with the ability of the soil to hold ample air, comes good gas exchange and drainage for rootage. All the other major cultural variables affecting growth are easily manipulated. Water, nutrients, sunlight, and to some degree, temperature can all be controlled easily. Aeration cannot and its consideration is as important as water and light to plant vitality. The breakdown or collapse of soil structure occurs at an exponential rate. If we imagine the usable life of a peat based container soil from a bag, it deteriorates from a reasonably good soil when fresh to unusable after 2 years. It's not unreasonable to expect the soil to lose at least 20-25% of its air holding ability by the end of the first growing season. In the first half of the second growing season, it will lose about another 25% of its air holding ability and in the second half of the second year, near total collapse is likely as the remaining 50% is lost. Though this is an example of an imaginary soil, it is very close to what actually occurs. Another way of saying it is: Even though a soil might be performing acceptably at the end of the first growing season, you should expect a rapidly accelerating collapse in the subsequent year. So, if you use a soil for 1 year and mix it 50/50 with a fresh, similar soil, 50% of the soil will have totally collapsed by the end of the growing season, and the other 50% will have lost about 25% of its ability to hold air. If a soil is not holding enough air, it's holding too much water. Water and air retention vary inversely in soils and when one increases, the other decreases. When soils hold too much water, you have to hope that the plant will use enough water or that enough water evaporates to prevent root rot issues and even minor cases of over-potting can mean terminal misfortune. At risk, I speak out often against the use of compost in container soils. It supplies nearly nothing in nutrients and clogs the soil macro-pores container gardeners should covet. Containers are not gardens and much of what works in the garden can cause difficulties in containers. Additional possible considerations are carry-over of fungal spores, the possibility/probability of insects in various stages (eggs, larvae, etc) and carbonate precipitates from your watering water. A slow soil will also have accumulated fertilizer salts and possibly insecticides that you may have applied and forgotten about last season. I suggest that container soils be turned into the compost pile or garden and fresh soil used in its place unless monetary considerations prohibit. Al

If it were me I would toss it, not because of the disease potential, but because it is too heavy for optimal results for most people. Consider the problems your plants are having may not be disease primarily, but the potting mix they are growing in saping the energy right out of them. You don't need to send it to a land fill, it can be dumped out on any patch of land. Perhaps you know a gardener with a yard who would want it?

I doubt apple is affected by TMV. But even if it is it won't be spread via soil or mulch. I believe on tomatoes it's spread by thrips.

David - this is written in a conversational tone, even though I disagree with you on a couple of points. First, the reason I don't reuse my potting soil, and I start with a soil that has as its primary fraction, large particles of pine bark, which takes 4-5 times longer than peat to break down, is that I have found it VERY advantageous to keep my focus on aeration. There are actually ways to quantify a good soil and compare it to a lesser soil by examining it's total porosity and air porosity at container capacity. Container capacity is the soils state of water retention after it has been completely saturated and has just stopped draining. You cannot achieve a level of either total porosity OR air porosity at container capacity using broken down particles of peat/compost/coir as the primary fraction of your soil, even with a considerable volume of perlite added. If you are left with nothing but perlite, which doesn't seem like something that would occur as a common scenario in normal cases of soil aging, then we really aren't talking about reusing an old soil; rather, we'd be talking about reusing the old perlite fraction, which is something quite different. So, if you are reusing the old soil as a significant fraction of the current soil, its very likely you're putting yourself at a distinct disadvantage because of the inherent reduction in aeration and probable excess water retention. I'm not pointing out these facts to disparage how you grow, only so we can understand that SAYING a soil drains well (or is well-aerated) doesn't mean it actually does (or is). We KNOW that fine particles hold more water than coarse particles (of the same material) and vine organic particles tend to compact, further reducing aeration and increasing water retention. IF you were to use inexpensive pine bark as the primary fraction of your soil, and add enough of your used soil to arrive at a favorable state of water retention, you would end up with a soil that DOES have favorable total porosity and air porosity at container capacity. If the soil is entirely broken down as you suggest it is, you STILL need to buy something to replace the lost volume, unless you're using compost ..... and then you end up right back where you started - so why not buy inexpensive pine bark instead of another finer ingredient? Something I wrote on another thread about rooting in water: Though roots form readily and often seemingly more quickly on many plants propagated in water, the roots produced are quite different from those produced in a soil-like or highly aerated medium (perlite - screened Turface - calcined DE - seed starting mix, e.g.). Physiologically, you will find these roots to be much more brittle than normal roots due to a much higher percentage of aerenchyma (a tissue with a greater percentage of intercellular air spaces than normal parenchyma). Aerenchyma tissue is filled with airy compartments. It usually forms in already rooted plants as a result of highly selective cell death and dissolution in the root cortex in response to hypoxic conditions in the rhizosphere (root zone). There are 2 types of aerenchymous tissue. One type is formed by cell differentiation and subsequent collapse, and the other type is formed by cell separation without collapse ( as in water-rooted plants). In both cases, the long continuous air spaces allow diffusion of oxygen (and probably ethylene) from shoots to roots that would normally be unavailable to plants with roots growing in hypoxic media. In fresh cuttings placed in water, aerenchymous tissue forms due to the same hypoxic conditions w/o cell death & dissolution. Note too, that under hypoxic (airless - low O2 levels) conditions, ethylene is necessary for aerenchyma to form. This parallels the fact that low oxygen concentrations, as found in water rooting, generally stimulate trees (I'm a tree guy) and other plants to produce ethylene. For a long while it was believed that high levels of ethylene stimulate adventitious root formation, but lots of recent research proves the reverse to be true. Under hypoxic conditions, like submergence in water, ethylene actually slows down adventitious root formation and elongation. If you wish to eventually plant your rooted cuttings in soil, it is probably best not to root them in water because of the frequent difficulty in transplanting them to soil. The brittle "water-formed" roots often break during transplant & those that don't break are very poor at water absorption and often die. The effect is equivalent to beginning the cutting process over again with a cutting in which vitality has likely been reduced. If you do a side by side comparison of cuttings rooted in water & cuttings rooted in soil, the cuttings in soil will always (for an extremely high percentage of plants) have a leg up in development on those moved from water to a soil medium for the reasons outlined above. Al