Specialty Gardening: Container Soils - Water Movement and Retention III , 0 by tapla

tapla wrote:
The gritty mix is excellent for cacti/succulents because it supports virtually no perched water to worry about (rotting roots). The 5:1:1 mix is still head and shoulders above most commercially prepared cactus soils, but not as good as the gritty mix because it does hold some perched water.

There is some confusion about the 5:1:1 mix's longevity. Personally, I only use it in containers that will go 2 growth cycles or less between repots, but that's just ME. Conifer bark, on a size for size basis, breaks down at about 1/4-1/5 the rate of peat and 'composted forest products'. Add the larger size of the bark particles, and it's much slower than that, even. Structurally, the 5:1:1 mix should outlast a peat soil by at least 6-7 times. In almost ALL cases, the plant needs repotting long before the soil is no longer servicable, something that can't be said about most soils based on fine particulates.

I use the 5:1:1 mix for my short term plantings because it's less expensive and easier to make. I realize I give up a small amount of potential, but I can live with that because plants are generally soo much more productive and healthier than those in heavier (more water-retentive) soils. Once you're used to the soil and your plants watering requirements, I think you would be pretty hard-pressed to discern any significant difference between the gritty mix and the 5:1:1 mix unless you get into trouble watering. The gritty mix is much more forgiving of over-watering, and growing in shallow containers.

If you use a soil that supports 3" of perched water in a 3" deep container, the soil will be 100% saturated after a thorough watering. That can't happen with a well made gritty mix.

Al