What Pam said ^^^; and, the most significant factors in determining whether or not a grow medium is appropriate are whether or not the soil contains anything phytotoxic and particle size. Container media do not wear out, even though this idea is often suggested. Soil particles just become smaller and smaller, which increases the amount of water a medium can hold while decreasing the amount of air porosity. There is no question it's better to err on the side of more porosity and water more frequently than to err on the side of too little porosity and see the planting suffer from poor root function or even wrecked root health. One cannot take a quart of fine material, like peat, coir, or sand, and "amend it by adding coarse materials like pine bark. That practice actually DECREASES o/a air porosity until the fraction of coarse materials becomes so large there is no longer enough fine material to fill the larger spaces between the coarse particles. Two observations about mixture reaches the "threshold proportion", which occurs when there is exactly enough fine material to fill all spaces between large particles: 1) It will have less aeration and be more difficult to grow in than peat, coir, or sand or a mix thereof. 2) Adding additional coarse material to mixtures at or beyond the threshold proportion such that the coarse material becomes a very large fraction of the medium (around 80%) quickly increases o/a air porosity. Container media is all about structure and its ability to retain that structure for the expected life of the planting. So, as Pam and I mentioned, there is little sense in reusing a medium, the structure of which is inappropriate. That seldom ends well. Used media can be used as the much smaller fine fraction we might add to coarser material when putting a medium together, but even then, particles of slightly larger size 1/20-1/10" (about the size of coarse ground pepper) would be the better choice. As in life, our growing experience and how much reward we're able to realize from our efforts is a product of the decisions we make. There's no judgement to be made about what a grower does or doesn't do, we all order our priorities differently, but that doesn't change the fact that what the grower chooses will always have an impact on how the plant responds. Al

I've never had much luck killing mealies with insecticidal soap - They've got some sort of waxy coating that makes the soap ineffective. I have found isopropol alcohol to be very effective, even at penetrating the wooly nests, but it can cause the plant to become dessicated if it isn't washed off after a few minutes. If your yews aren't too big, you could just dump some isopropol alcohol into a sprayer and douse the tree with that, then hose it down after a minute. The alcohol kills anything it's going to kill right away, so there's no point in leaving it on. If you do this every week for a month you should have killed most of them off, as their life cycle is about 30 days. There is a product called Safer's Fine Oil Spray, which is supposed to dissolve the waxy coating, making them susceptable to the insecticidal soap. I've never used it, or even seen it for sale for that matter, but if you can find it, it might be worth a try. Particularly if you don't want to use the alcohol BP

Ants aren't green. And they don't infest plants. More likely you have aphids. Wash them off, and repeat every several days until no more return.

Mealy bugs are close relatives of Aphids and can be treated the same, spray with a sharp stream of water to knock them off the plant, repeating as necessary. There is no need to use Rubbing Alcohol (that can be harmful to plants) or any kind of oil. Since most all pests go after plants that are not as healthy as they should be check the soil these plants are growing in to be sure it is good and healthy and can grow a strong and healthy plant that will better withstand an insect invasion.