FWIW - I wrote & posted this about using H2O2 in containers a number of years ago and several times since. H2O2 has an extra O atom (compared to H2O) in an unstable arrangement. It's the extra atom that makes it useful in horticultural applications. Generally, we're not concerned with aerobic forms of bacteria normally occurring in container media or on roots. Since H2O2 is an unstable molecule, it breaks down easily. When it does, a single O- atom and a molecule of water is released. This O- atom is extremely reactive and will quickly attach itself to either another O- atom forming stable O2, or attack the nearest organic molecule. Reduced O levels and high temperatures encourage both anaerobic bacteria and fungi. Many disease causing organisms and spores are killed by O, and the free O- H2O2 releases is very effective at this. Additionally, when plants growing in water-retentive media are treated with H2O2 it will break down and release O into the area around the roots. This helps stop the O from being depleted in the water filled air soil air spaces until air can get back into them. High O levels at the roots will encourage rapid healthy root growth and discourage unwanted bacteria/fungi. I know H2O2 comes in several different strengths, the most common of which are 3% and 35% solutions. Least expensive is the 35% product (what I use) which you dilute (to an approximate 3% solution) by mixing 1:11 with water. I have used the 3% solution at 1 to 2 tbsp per gallon as a cutting dip/soak, and have mixed it into irrigation water for plants in extremely water retentive soils at up to 3 tbsp per gallon, both with good results and nothing adverse apparent. H2O2 in high concentration is a powerful oxidant and quickly oxidizes almost anything it contacts, so be careful with it if you use it. A solution that is too strong can destroy any organic molecule it contacts. I've seen this chart posted several times as suggested strength solutions for use in watering plants. You may wish to start at a lower concentration , such as I've used, and experiment. TO THIS AMOUNT OF WATER ADD THIS AMOUNT OF 3% HYDROGEN PEROXIDE --OR-- ADD THIS AMOUNT OF 35% HYDROGEN PEROXIDE 1 cup, add 1-1/2 teaspoons ... 35% - 7 to 10 drops 1 quart, add 2 tablespoons ... 35% - 1/2 teaspoon 1 gallon, add 1/2 cup ... 35% - 2 teaspoons 5 gallons, add 2-1/2 cups ... 35% - 3 tablespoons plus 1 teaspoon 10 gallons, add 5 cups ... 35% - 6 tablespoons plus 2 teaspoons 20 gallons, add 10 cups ... 35% - 3/4 cup plus 1 tablespoon plus 1 teaspoon 1) you can use them together w/no problems, but you shouldn't need it if you're watering correctly & the gritty mix is made even CLOSE to the suggested recipe. 2) Plants are reactive organisms. They will reach favorably to increased O2 in the root zone, and unfavorably to reduced levels. If you use excessive amounts of H2O2, it can kill viable tissues, so don't over use it. 3) Your plants won't get addicted to H2O2 to any greater degree than they are addicted to water. I would urge you to lift the plant from the pot & take a look at the roots to see what's going on, then prune roots back to sound tissue if you find rot as an issue. At that point, a dunk in a solution of H2O2 or unscented household bleach might be an appropriate measure. Al

When we measure pH, we are measuring the concentration of hydrogen (H+) ions in the irrigation water or soil (nutrient) solution. As a guideline, water for irrigation purposes is usually best if its pH lies between 5.0 - 7.0. The measure of alkalinity gives us the water's ability to neutralize acidity. The level of bicarbonates, carbonates, and hydroxides in water determine its alkalinity. The desirable alkalinity range for irrigation water is 0 to 100 ppm carbonates, with 30 - 60 ppm optimum for most plants. Whenever you test the water you'll be using for irrigation, you should always include the measure of both pH and alkalinity. A pH test on its own, does not give any indication of alkalinity. Water with high levels of bicarbonates or carbonates (high alkalinity) always has a pH value >7, but water with a high pH doesn't necessarily have high alkalinity. This is a very important concept because high alkalinity exerts more significant effect on plant nutrition and the fertility of growing media than pH. High pH irrigation water generally causes no problems as long as the alkalinity is low. Since high pH water with low alkalinity has little ability to neutralize acidity, it's effect on media pH will be minimal. Cause for more concern are situations where you must utilize water having both high pH and high alkalinity for irrigation, which will cause the pH of the growing medium to increase substantially as media ages. If your water analysis is known to be alkaline, you may need to significantly reduce the addition of compounds containing Ca or Mg because of the dilute solution of limestone in the water. The smaller the container - the more serious the issue because small volumes of soil offer less buffering to pH change. In high alkaline situations, you can often expect/experience Ca and Mg deficiencies along with micronutrient deficiencies (both real and antagonistic). Acid forming fertilizer will not actually lower media pH as long as there is limestone in the soil - unless the soil is acidic already, but vinegar (and other acid) applications will help to neutralize alkalinity in the irrigation water, which will be helpful. Al

The gritty mix uses bark as a filler and as a reservoir for moisture and nutrients. I never use it at more than 1/3 of the op/a volume of the medium, which ensures that as the bark breaks down the soil won't collapse. Collapse in this sense means the bark breaking down into pieces small enough to fill the macro (air) pores between the mineral fraction of the soil. The Turface or calcined DE serves the same purpose. The grit is used to adjust water retention od the soil, which would be very difficult to do if using only bark and Turface, ant you would need to use so much bark in a 2 part bark mix that soil collapse would be a distinct possibility if you don't repot yearly. In a perfect world, the mineral fraction would be uniformly about 1/8" in size. The reason is, the perched water table disappears as uniform particle size becomes >1/10". The ideal bark size would be 3/16-1/4". The slightly larger than ideal size allows for some breakdown in the bark particles w/o having to deal with perched water. All in all, there is a lot of thought that went into determining what optimum sizes are and what ingredients work best. The concept embodied in the soil is actually more valuable to growers than the recipe. Soils that primarily hold water inside of soil particles, and some water at the interface where particles contact and on the surface of the soil's particles, offer much greater opportunity to reach their potential. Oxygen-robbing water held in the spaces between soil particles are the bane of root health and function. Growers who find the basic 1:1:1 ratio of screened bark: screened Turface: grit doesn't hold enough water, need only to change the ratio of the ingredients to favor the volume of Turface while reducing the amount of grit to increase water retention, or simply adding additional Turface would accomplish the same goal. @ examples for more water retention are: 3 screened bark 4 screened Turface 2 #2 cherrystone or grower size grit 1 screened bark 2 screened Turface 1 #2 cherrystone or grower size grit Generally speaking, the more you NEED to water, the better your plants like it, as long as you water often enough that drought stress isn't a factor. Al

One thing we need to respect is another's perspective. One grower might look at growing with the attitude that nothing is going to stand in the way of my reducing the effects of every limiting factor that impact my plants' growth and vitality. Growers like this tend to look at growing from the plant's perspective. Another grower might not be interested in entertaining the thought of changing anything, so long as the plant seems to be doing well enough. I've found this to be especially true if the chance involves more effort or expense - this is more a view from the grower's perspective - how it affects ME, rather than the plant. Neither perspective is wrong, they're just different ways of looking at things and ordering priorities. We all go through the same considerations, but some people come down on the plant's side & others on the grower's side. A prime example of this can be seen in the form of people arguing vehemently against the effort involved in finding ingredients and then making either the 5:1:1 mix or gritty mix. Almost always, the argument against comes from growers who have never tried either mix, and are content with the results they get from a from-the-bag mix because it's easy. Not all of us orders our priorities in that fashion. My good enough may be her poor; and good may in fact not be good enough for her. I know a lot of people like that and admire them for their desire for continual improvement. Rachel's question is a very good one, and her commentary clearly illustrates she's been thinking the issue through (from the plant's perspective) and looking for some input. Any teacher would give her high marks for that. I say often that our plants are already genetically programmed to grow to be beautiful specimens. The ONLY thing we can do to help is to be proactive in continually reducing the effects of ALL things that have the potential to limit growth/vitality. Remember, if everything is perfect except ONE thing, that single limitation can wreck the entire growing experience. One thing for Rachel to consider is that water in plunged pots behaves differently than it does in conventional container culture. That they are partially buried turns them into mini raised beds, hydrologically speaking. As long as they are not plunged into clay, the earth will quickly wick any perched water from the soil she chooses; so she has roughly the same potential for growth/vitality using soils that would otherwise be too heavy (water retentive) to be well suited to container growing as she does if using the gritty mix or the 5:1:1 mix. Since there is little notable loss in potential, based on her growing method, if using a heavier soil, we need to look to the interval between when the pots are lifted and moved indoors and when they're returned to the garden or beds and buried. Normally, there would be considerable concern over accumulating salts during the over-wintering period; this, as a result of having to water a heavy soil in small sips to avoid the soil being wet for any extended period. Since I believe she will be watering rather infrequently, it may not be a serious issue. Just a guess - if she's watering less often than every two weeks, I think she should be ok until repot time. Also, if she's willing to cheat the state out of a little rain water and use that to water with, it pretty much makes it a nonissue. I think Rachel's free to use a heavier soil if she wants to, and it shouldn't have any notable effect on her plants. If she has a suitable bark on hand - maybe something like a 5:2or3:1 bark:peat:perlite would be good - or even a bagged soil. The only real disadvantage to a peaty soil for this particular application is that it makes repotting more difficult. So - there's a little about perspectives and growing for you to consider. I hope there's enough there for you to set course with a little greater degree of certainty. Time to get out in the yard before it gets too hot again. It looks like another day that will be pushing 100*. Take care - thanks for the kind words. ;-) Al