If a gritty mix has no PWT then how can it be to wet?
PWT isn't everything. Different plants have different needs. If you put an epiphyte like an orchid in gritty, it would be easy to overwater it.
I've found that gritty mix can indeed have perched water, and a lot of times does. While it's minimal, it is there. Screening turface with insect screen leaves enough small particles that you get a small amount of perched water. Try watering a container, and once done, lower the pot in your arms quickly, and in a sharp motion stop and move it up (like a yoyo perhaps); water will come out of the drain hole. You can do this several times and force water out. Unless I'm mistaken....that's perched water. As nil said, with water sensitive plants, you can easily over water in gritty mix.
Compared to traditional peat-based soils the standard gritty and 5-1-1 mixes have minimal amounts of perched water.
I have a number of trees growing in 5-1-1 mix at the moment and there is very little perched water. Last week I inserted a toothpick into the drainage holes of my containers and noted only a few extra drops of water, certainly nothing significant that would harm roots in my opinion.
On the other hand, I've seen quite a few peat-only containers that were nothing but a soggy mess at the bottom of the container but nearly bone dry at the top.
If there is any concern about how much water the gritty or 5-1-1 mixes retain then you could adjust your soil mix and increase the amount of drainage material (granite or perlite) and cut back slightly on the Turface, DE, or peat. That's what I like about these soil mixes. You, the grower, can determine how much water you want to retain by how you mix your soils.
Thank you for your responses, I understand everything discussed. My question is can a gritty mix be too wet after you eliminate the perched water. My understanding is that wetness doesn't kill roots but the lack of oxygen does. So with plenty of oxygen and no PWT how can a gritty mix be too wet?
I'm curious about why you are asking this question. Do you have a plant in gritty mix that you think is "too wet"? I've got a lot of different kinds of plants in gritty, including succulents and cacti, and have never felt they were too wet. Too wet means to me that some of the roots are at risk of rotting due to lack of oxygen at the root level. If you make the mix with appropriate ingredients, screen your ingredients so there are no particles smaller than 1/16 inch and you have enough drainage holes, I don't see how it could cause root rot or be too wet. Or maybe I should ask, too wet compared to what?
I have read many treads about the gritty mix (I just planted a couple of citrus in it) with people trying to figure out different ratios to get the right wetness. This didn't make since to me because everything i have learned you cant have too wet if there is no PWT in your soil. I haven't read any treads that discussed this element of the gritty mix and thought i would get peoples opinion.
"you cant have too wet if there is no PWT in your soil."
This is incorrect. Too wet depends on the plant not PWT. Some plants don't mind PWT. Some plants hate it. Some plants can't have any water whatsoever at certain times of the year regardless of how freely draining the medium is. Some plants can only handle their roots getting momentarily wet and then drying out.
Now if you have a plant that likes the airspace:available water ratio that is in the gritty, then you can't overwater. But that is for that plant specifically. A mix that is impossible to overwater for one plant could be too wet for another type of plant.