I don't know where you read/heard that the Three Rivers flagstone will leach iron, but it isn't an issue in the middle of a garden as a path, and it would be my first choice as the colors really pop, don't waste your time sealing it, just hose it off from time to time. I also wonder if you really need to pay the premium for a tumbled flagstone, the raw Three Rivers flagstone is cheaper and just as nice. In California USDA zone 9 locations, an inch or two of sand is all that is necessary for a leveling base of flagstone used as a stepping stone pathway. If you have clay loam based soil that is too soft, you may have a drainage problem needing correcting, or are just overwatering the area. A clay loam soil is only too soft and subject to compaction after significant rains,(and this is really only an issue for planted areas, where you want to avoid soil compaction when the soil is wet, so you maintain good oxygen exchange and soil texture for plant roots). Even in the middle of winter after heavy rains, a clay soil is fully capable of supporting the weight of flagstone pavers without problems of movement, but the sand base will help make them more stable. Weed fabric below a base material is really only appropriate/necessary when you are wanting a solid area of flagstone paving and want to reduce weed growth at the joints; when laying out more widely spaced flagstone as a path, I'd think you would want some low ground cover between the flagstones. If you don't, then use the weed fabric and mulch with gravel or decomposed granite between flagstone pavers. If you are trying to lay flagstone stepping stones on a slope, there is considerably more attention to a stable base necessary, and I'd suggest you get professional help to install it for better results. I'd also suggest you go to your local library or buy one of the Sunset or Ortho gardening books that address landscaping and dry laid flagstone paving, they both cover all the issues you will likely face in your installation, and are generally a more reliable source of information than asking questions on the internet. If you are really interested in the best methods for installing a lower water use garden using California natives, you should also do some reading up on issues of soil drainage, best time of year for planting, how and when to water, importance of mulching, etc., as there are better ways to do this to save time, money and water.

I don't put any sulfur in the holes of the roses pictured. The other holes with sulfur didn't bloom well. My heavy clay is very retentive, there is no leaching here. Here's a quote from Nutrient Stewardship site: "Phosphorus is the nutrient most affected by pH. ..Nitrogen, Potassium, and sulfur are less affected. At alkaline pH values, greater than pH 7.5, phosphate ions tend to react quickly with calcium (Ca) and magnesium (Mg) to form less soluble compounds. At acidic pH values, phosphate ions react with aluminum (Al) and iron (Fe) to again form less soluble compounds." It's good to test if one's tap water is alkaline, some cities add lime to water so pipes won't corrode. Calcium in lime will bind with phosphorus, and less is available. In my 12 years of growing flowers in pots, the year that I got continuous MOST blooms despite my pH 8 water was when I used high phosphorus SOLUBLE fertilizer, and low nitrogen. Granular phosphorus like bone meal and 46% superphosphate are useless in the planting hole here in alkaline clay. My results confirmed what University of Colorado stated "bone meal and rock phosphate can only be utilized at or below pH 7". My pH 7.7 soil was tested most deficient in phosphorus. Here's a quote from David Neal, CEO of Dyna-Grow Plant Nutrition in CA: "There is some evidence to believe that low N helps to convince a plant to stop its vegetative growth and move into its reproductive phase (flowering), but environmental factors are probably more important. P is typically 5th or 6th in order of importance of the six macronutrients. There is little scientific justification for higher P formulas, but marketing does come into play ...." He's right, just a tiny bit of SOLUBLE phosphorus made more blooms and more roots - but beyond that is wasteful. The site, Robert Morris NOBLE plant foundation, rated the mobility of NPK: "Let's compare the mobility of NPK on a scale of 1 to 10. Nitrogen is a 10 ... extremely mobile and can be lost to leaching. Potassium is a 3. It has limited movement in the soil. Phosphorus has a rating of 1. It is immobile in the soil and is likely to stay wherever it is placed." Here is a link that might be useful: Soil pH and availability of plant nutrients

I might use a concrete stain rather than the iron solution, just in case. mosses like a mildly acidic soil, but doens't need RICH soil, so I've foind that either buttermilk or vinegar can be used to change the PH... testing it with litmus strips is easy. and test if fairly regularly, since concrete tends to leach alkyline into the soil (not as much of a prblem with 50 year old stuff, but never hurts to test) it's always best to put moss into as identical a situation as you can from whence you took it...from rock to rock, from dirt to dirt, from bark to bark... but the regulars at the moss board might have other hints.

Great topic, and I think we need to do another one in mid July when things are really growing! Mine pales in comparison, but you have to realize that this garden is only a month old. We built a new addition to the house which meant a new garden from scratch. It looks better in person than the pictures. Once our humongus crepe myrtle are in bloom, along with the other wild flowers, it will look so much better!