We don't replace soil in raised beds because we have the earth below creating movement of water and air in the soil. Raised beds are earth based gardens. Containers are completely disconnected from the earth by virtue of being containerized. The concept that I want you to understand is this: Water doesn't move unless air does. A simple example is a drinking straw in a glass of water. Dip it in and place a finger over the top of the straw. Withdraw the straw and the water doesn't move out of the straw. Remove the finger and the water runs out because now air can enter. In the earth water is constantly moving through the soil and therefore so is air (the earth has no drainage hole where the water exits the system). In a container the water runs down and out the drainage hole and then water movement stops and therefore so does air movement. This is why containers and the earth are so different. In a container we need a coarse mix that allows the free movement of air and water (drains well). In the earth we can get by with tighter soils because water still moves and thus air still moves. A potting mix is only as good as it's particle size. If you purchase a store bought mix it will probably be just fine in the first year, but the organic part of the mix gets broken down by biological activity and weathering. As it is broken down it breaks into smaller and smaller particle sizes and before long the smallest particles which wash to the bottom of the container are getting closer and closer to having clay soil in the container. This holds a lot of water and very little air which plants need. Miracle Grow soil is peat based and peat based soils are generally good for one season and sometimes 2 if they aren't exposed to the elements any longer than necessary. After that they are so collapsed/broken down that they will have an adverse affect on plant performance and should be dumped out into the earth based garden and replaced. For more info, please visit the container gardening forum.

I routinely dump "spent" potting soil in my flower beds, wherever they are most in need of organic matter (which is almost anywhere). It doesn't seem to hurt things at all. Some of my containers are so large that replacing the potting soil would be impossible. It sinks down or somehow decays and vanishes in the pots over time, and in those large pots I simply top-dress with more potting soil and a bit of organic slow-release pelleted fertilizer. Some of my very large containers are planted with bulbs, and the bulbs generally return to bloom for two to three years. If they are tulip bulbs, at the end of the second or third summer (after the foliage has faded), I root out all the small tulip bulblets remaining (that applies to the still-liftable containers as well) and plant those bulblets out in my xeric front garden. I'm lucky--I have the perfect climate for perennializing tulips, because the bulbs slowly recover, usually putting out only foliage for a year, and then blooming every or every other year depending on type. The crocuses I either re-pot in the next series of spring bulb pots, because even the tiniest bulbs will bloom, or gather to plant into my lawn. Hyacinths I plant out in my more shady, sheltered back garden, where they slowly recover but never are quite as stubby and heavy again. I kind of like them better a little looser and thinner in the open garden. Daffodils--I thin those, reset some in the pots, and the rest go out in my sheltered, shadier back garden to do what they can. If things are too far along when I'm clearing out containers of bulbs and/or annuals, then I simply dump the "spent" potting soil into my compost bins/heaps, and eventually it all ends up out in the garden again. Lisa

funkyhat I do not know much about bugs, but read some about aphids - IIRC they do not lay eggs in soil. I do not have lots of info, but here are some of my notes: ..." Aphid sexuality is quite complex, including both asexual reproduction concluding with live birth and sexual reproduction concluding with egg laying. In spring, when hatching occurs, all emerging aphids are female and reproduce asexually, essentially giving birth to three or more clones of themselves every day. As the end of summer approaches, the reproductive strategy of aphids in climates with cold winters shifts and both males and females are produced. After mating, the sexually reproductive females deposit eggs in the protective crevices of plants; safe from harsh winter weather, these eggs hatch the following spring and the cycle begins anew... ...Each of the many aphid species has its own life cycle, but there are some features uniting nearly all of them. One feature most species share is that they are incredibly prolific. Wingless adult female aphids can produce 50 to 100 offspring. A newly born aphid becomes a reproducing adult within about a week and then can produce up to 5 offspring per day for up to 30 days. An even more amazing feature of life cycles of most aphid species is that reproduction during at least part of its life cycle can be accomplished without the help of male aphids! Babies have no fathers.Young are born from females without the benefit of sexual reproduction, in a process known technically as parthenogenesis. When mother aphids reproduce parthenogenetically, instead of laying eggs they give birth directly to smaller editions of themselves"... If you are sure there are eggs in the soil, perhaps they are different pest.

For 15" depth, change the ht of the layers to 3,3,3, and 5" respectively. It doesn't matter if the planter is on legs or a concrete slab, water retention and drainage will not vary so you could notice. If you set the planter on a slab, you'll gain some geothermal heat through the bottom, and you can retain some of it by way of the insulation at the sides and by mulching heavily for the winter. If you set it up on legs, you might as well not bother with the insulation. You'll have eliminated the heat gain via conduction through the bottom of the planter. While the insulation might cause a lag in how fast the soil temperatures move upward and downward in the planter, it won't offer enough protection against ambient temps of say 0*F to save plants for which that represents a killing low. In order for insulation to work, you really need an extraneous heat source you can trap in the planter. Example: Take a plastic cup of water and put it in the freezer. At the same time, put a cooler with a plastic cup of water in it in the same freezer. Within 3-4 hours, the cup alone will have reached the same temperature as all the rest of the freezer's ingredients. The cup/water in the cooler that's in the freezer will take much longer to freeze and to reach the same temperature as the rest of the freezer's stores, but within a day or so, it will be the same temperature as the frozen water in the cup that's unprotected by the cooler. Wire a small light bulb so it's inside the cooler (an extraneous heat source), and the story changes markedly. Example: If you have a plant in an unheated garage over-wintering at head level, and one setting on the garage floor, which is warmer? The one at head level, even though there is SOME heat rising through the floor. Now, cover the plant on the floor with an over-turned cardboard box to trap extraneous heat rising through the floor. NOW, the plant under the box is warmer by 10-15*F than the plant on the head level shelf. Al