Does it have to be wood? Metal pipe is cheaper down here than any wood bigger than a 2x4 so we use it. Not the thinwall stuff like they use in chain-link fences but the thick walled drill pipe. Lasts longer too. If you have to go with CCA I'd allow for a good size perimeter. Found this at Ecology Center Leaching of arsenic from PT CCA wood in raised garden beds has been found to be limited to about 6", but that 6" is permanently contaminated. It means that you should not grow vegetables in that strip nor can you turn that soil into the rest of your garden. You'd want a clear work/walk path between the fence and the outside of the garden anyway, right (wheelbarrow, tiller, hoe handle length, etc.) so if the above is valid then 5 feet or so should be enough. Dave

Tom: I have no idea if you are right, or wromg, only that according to our local home center, the treated lumber that has been sold for several years now has no arsenic in it. But I use oil based semi-transparent stain on all treated timbers, so it's really not an issue with me and the new ones seem to stain the same as the old ones did. We have given up on cedar. It's too soft, rots faster and costs too much. A few coats of stain, and you can't tell the difference looking at it anyway. I've also never had a problem with plants in treated timber raised beds, as we always lined them with aluminum flashing to prevent soil from escaping. It may also have prevented leaching. Or, it could have been the sealer. I can't really say. But now with the copper, I had to find something else and finally settled on the extra heavy black plastic used for lining ponds. Actually, the best timbers on our place are the RR ties that surround the barn and line the paths to the pastures. Talk about forever! Some have lain out there for over 40 years and are still sound, but it takes two strong men and a gorilla to handle them.

Ok, here's a crude calculation just to give you an order of magnitude. Let's suppose you had 10 lb of ash, and it was dug into a 5x5 ft area to a depth of 1 ft. While searching for the actual formula of CCA, I ran across a paper on the metals content of CCA treated wood ash, so I could skip some steps. CCA was made in two grades, 0.25 lb CCA/cu ft of wood and a higher grade 0.4 lb/cu ft. Their sample was 4 kg/m3 which works out to about the 0.4 type. The ash was about 20,000 mg/kg (ppm) Cr, 10,000 ppm Cu and 11,000 As. After a bunch of conversion, that comes out to 36 ppm of additional arsenic added to the 5x5 area if distributed a foot deep (using 1.5 tons/cu yd of soil). I picked As because it's the most toxic of the three metals. Now this is above health-based guidelines for residential soil, which are in the range of 5-15 ppm. Note, those numbers are based on your entire yard being at that level, and living on it for a very long time, with a resulting risk of death from cancer or non-cancer health effects reduced to essentially nothing amongst all the noise of other risks in life (i.e. a rate of 1 in 100,000 or 1 in 1,000,000 excess deaths). You will not experience arsenic poisoning from this soil in the way that you're thinking. It's more like a small incremental increase in health risk, much like smoking a cigarrette (or a whole pack ) won't kill you, but it's not particularly good for you. Here is a link that might be useful: CCA Ash Analysis Paper This post was edited by toxcrusadr on Wed, Nov 20, 13 at 12:00

I have used Serenade/Rapsody/and another name for years. It was first Serenade, then Bayer bought it. They then put out a natural line of pesticides that they eventually sold the license, I believe it still found in the same shape bottle, but I do not remember the name. Bayer still control the license for the product for agricultural/professional use under the names Serenade and Rapsody, but the name of the product for homeowner eludes me, since I can buy Rapsody. I have found it to be a good fungicide spray, when rotated with another spray. One week spray with Serenade and in two weeks another chemical or natural product. I find that is true for all fungicides. They need to be rotated. It has been proven it now helps as a soil drench product for root rot, but no where as good as it is as a spray for leaf fungus. I honestly have never used it for rust. I have used it for BS and powdery mildew and root rot, but never for rust. I honestly would alternate, but first test a small spot on your plant. Unfortunately they have not been tested on succulents, so the bottle will not tell you if it is safe for your particular plant. I don't know if sulphur or copper are safe on succulents, but they are both very effective treatments of rust. You do know that no spray will alleviate the damage that has been done. It will only prevent it from spreading.