The finest-ground and thus for this purpose most useful ground bark is labeled "soil conditioner" at the garden centers. Here it is a bit less than $3 per 2-cubic-foot bag. I'll bet I have used 100 bags in the past several years and have seen no apparent problems.

Hi Laura: As Jacqueline, Tessie, and JeriJen often said: "location, location ...." Tapla's recipe of 5 parts fine mulch, 1 part peat moss, 1 part perlite is best for climate like mine: low-sun, flash flood warning and fast drainage is a must. It is recommended by Douglas Green, an owner of a large Ontario nursery of many plants in pots, including roses. If I use Al's 5-1-1, there is no need to put loose gravels or bark nuggets at the bottom for fast drainage. However, I use super-slow draining MiracleGro in green bag, and medium-slow draining Organic MiracleGro. I skipped this important process of putting loose stuff at the bottom, and regret it terribly. Now I have to dump the soil out of each pot, and start all over. I realize this after a heavy-rain simulation with a hose, with the pot flooding over and loses 1" of soil - which happens every time it rains here! Sure, Field Roebuck said it's not important, just put a paper towel at the bottom of the pot, and fill up with soil. His Texas climate doesn't have the low-sun, and 6" of rain flash flood. Each region should have its own recipe of best potting soil. Now I realize that the regular MiracleGro potting soil (green bag) might have been made for indoor pots, where one puts 1 measly cup of water per week. It's not meant for several outdoor heavy thunderstorms with 4 to 6" of rain per bout like my climate.

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

Plants can grow in just about anything if given the other conditions they require - sunlight, water, oxygen, and nutrients. But how well they will grow and produce with the least amount of input and attention by the grower when growing them in containers is entirely dependent on the media or potting soil. A durable, textural mix that is fast draining and not excessively water retentive is best for most plants but these are next to impossibe to be found premade and most are custom mixes like the 5-1-1. Something like Miracle Gro or ProMix can make do, but they are not the best and seldom get recommended by experienced container gardeners:-) And most prefer their media fertilizer free, opting to control fertilization according to the plants' needs rather than the manufacturers' assumptions.