Specialty Gardening: Dealing with Water-Retentive Soils , 1 by tapla

tapla wrote:
To ensure good drainage in container soils, you need to START with large particles. You can't add large particles (like perlite) to fine particles (peat/compost/coir) and expect them to increase drainage r lower the height of the PWT. It just doesn't work. What perlite does is take up space that would otherwise be occupied by water-retentive material, so all it does is reduce the VOLUME of water in the PWT of soils. It really doesn't improve drainage or aeration. I use the illustration of perlite and pudding. How much perlite do you need to add to pudding to get it to drain well & improve aeration? Maybe 60-70% perlite and 30% pudding is a start, but then you're really adding the pudding to perlite because perlite is the largest fraction. It works the same way with fine-particled soils. If you start with bark, and add enough peat or compost until you have the desired water retention, you're in much better shape from the perspective of drainage/aeration.

Try a mix of screened perlite and screened Turface for your seedlings. Practically speaking, it's sterile, and seedlings insist on good drainage and lots of aeration to grow well.

Raised bed soils are a horse of a different color. Raised beds are like growing in the garden, but conventional container growing is more like hydroponics than growing in the garden. Most often, I find myself helping those who are trying diligently to bring their gardening practices to container culture and have met with difficulties. Raised bed soil composition isn't as demanding as container media. Sand mixed with 30-40% organic matter will work well in a garden, but is often death in a container because although sand usually drains quite well, it's so fine that organic particles like peat & compost clog the macro-pores and increase water retention/reduce aeration. When I think of 'sand' for containers, I'm thinking of a material of uniform size like crushed granite/silica/pumice in particles of 1/16" or larger.

The soil in my raised beds:

Al