Specialty Gardening: Container Soils - Water Movement and Retention IV, 1 by RickCorey_WA

RickCorey_WA wrote:
Thanks again, Al. I repeat your message every time someone wonders why their seedlings or plants died from root rot.

There's one part of your message that I want to repeat, because it took me the longest to learn.

If you have a mix partly mixed up, and it's very coarse and gritty compared to what most of us have used for years, or bought in a bag ...

and you are tempted to increase water retention, (as I am), by adding "some" traditional peat-based potting soil such as Fafard or ProMix or Sunshine ...

Don't.

Or at least, never add more than 12% to 14% (1/8th to 1/7th).

Remember that the POINT of the gritty mix is to create open voids and channels for water and gas to flow through. Your gritty mix might only HAVE 10% to 20% open space. You probably already have some bark powder and fine bark fibers. How much "fine stuff" you already have depends on how you screen your bark and how much composting broke it down.

If you add 15% peat moss, or sand, or anything very much smaller than 1/10th inch (2.5 mm), you are FILLING the voids that you just went to great effort to create.

So aim to add less than 10% peaty stuff, if any. I now lean towards easing up on carefully I screen out all the bark fines, instead of deliberately adding any peat.

I keep making a big, nice batch of excellent texture, then ruining it by adding twice as much peat as I should have.

Then I have to re-make the whole batch, doubling its size to dilute the evil peat fines , and discipline myself to add NO peaty stuff.

I wish I could think of something that would bind up peat fibers and powdered peat, and bark dust, into some kind of sturdy, porous pellet like a clay ball or 2 mm x 2mm peat-ped. Then it could retain some water without filling all the pores in several cubic inches of gritty-mix.