Lime provides a source of Ca and Mg and raises the pH of media that in most cases would have a pH level too high for most plants. Keep in mind that pH is measured on a logarithmic scale such that a pH indication of 5.0 indicates 10X the acidity of a solution with a pH of 6.0. The pH of mostly organic container media should be about a full number lower than what would be considered ideal for the same plant in a mineral soil. Compare:

Chart for mineral soils:

For container media:

Maples do well in containers where pH is around 5.2-5.5, so you should lime your 5:1:1 mix, which can come in at anywhere from 4.0-5.0 (even lower if the bark wasn't turned often/often enough while aging in windrows).

The effects of the actual lime application won't last indefinitely, and your irrigation water has a significant impact on what happens to media pH in containers. The Mg fraction of dolomitic lime is about 125X more soluble than the Ca fraction, one of the reasons the Ca:Mg ratio should be something like 3 to 5:1, Ca:Mg. Usually, and what would happen if you were using deionized water to water with, the Mg fraction would be exhausted before the Ca fraction. That usually doesn't happen until mid-late in the second growth cycle of the plant in the same soil. At that point the grower should watch for Mg deficiency symptoms, which can be corrected at that time with the inclusion of a very small amount of Epsom salts each time you fertilize. Keep in mind that if the Ca:Mg ratio gets too far out of balance, Mg can become unavailable even if it's present in the soil at levels high enough that there wouldn't normally be an issue. An over-abundance (toxicity) of Ca can cause an antagonistic deficiency of Mg.

Soils like the 5:1:1 or gritty mix that can be flushed regularly without concern for significant loss of potential are very helpful in keeping your nutritional supplementation on track. For instance, if you were using a fertilizer like 20-20-20 or 5-15-5, P can very quickly accumulate in soils with the potential for causing any one or more of several issues. When you can flush soils at will, the flushing is like hitting the fertilizer reset button and preventing the badly skewed ratio of nutrients in the soil solution from causing issues. It's always beneficial to use fertilizers that closely mimic the ratio at which plants actually USE the nutrients, but that's especially true when using heavy soils you can't flush w/o loss of potential. In these soils, watering in small sips to avoid root health/function issues results in nutrient ratios that don't even come close to matching what the plant uses.

Al

Thanks Al. Now i understand it alot more..