"place gravel on the base of the planters (although I know this creates a perched water table) and put the fabric over that and then put the potting soil above both"

I'd recommend this, even though it does raise the perched water table and cuts down the amount of soil the roots have to grow it.

This will create an aeration layer at the bottom where the roots will be able to get a lot of oxygen. This fall I dug up some eggplants & pepper I had grown in container and saw this effect. The roots at the bottom of the tub were thick, healthy, and white even though they were growing in soggy soil.

Now if you are going to use a gritty mix for the soil, then this doesn't apply. But given you've been hired by someone to do this for them, they probably are not the type of tree owners that would water them as much as a gritty mix would require.

So for a heavy mix the rocks & landscape fabric can provide a beneficial aeration layer.

Here is a link that might be useful: Shows roots at bottom of containers

I'm not getting a clear picture of what these planters actually are, but if they're what I think they are, I would put a brick in front of each of the drain holes, then mound peastone around the brick so only the brick & hole are covered, then fill with soil.

The gritty mix would actually be a very good choice. If using a mostly organic soil, you'll get a LOT of shrinkage in a short time, and structural collapse is likely to become an issue before long, as well.

Do you/homeowner have a plan in place for root maintenance?

Al

The trees are pear espaliers and I think the planters are large enough (about 50 gallons) to train the same as in ground. The property is a multi-million $ estate so I don't think I could leave a pile of gravel and loose bricks beyond the planters. How would outside the planter be different than within?

I made a mix out of well composted wood chips (pure humus), peat moss, sand, perlite- 30-30-20-20 by volume. Just enough ashes to get pH around 6. Only the peat will shrink much and the mix should continue to drain adequately even with that shrinkage. The compost holds water very well.

The brick & peastone goes inside the container at the drain openings.

You're going to have a VERY water-retentive mix that will shrink quite a bit annually. I also think that dolomite would have been a wiser choice than the wood ashes, which are very high in soluble salts.

Best luck - I wish you well.

Al

Dev, there is a means for water to escape as described in my original message- each planter has 3, 3X6" openings at base of front wall of planters. Not sure if it will be adequate but I'm trying to do the best I can with what is there.

I manage (own) a nursery with quite a few bearing age fruit trees in large containers filled with a similar mix and the containers drain well enough- even during long rainy periods. I don't believe these containers have relatively that much more drainage exit although they surround the base of the pots.

Pears function well in wet conditions and given the size of these containers I think they will do well even if as much as a third of the mix remains soggy most of the time.

harvestman, it sounds like you have had some successful experience so I would follow your own instincts. :-)

I work in an area with steep terrain so we end up building a lot of retaining walls that often have planter boxes attached. Often times the footing of the retaining wall extends under the planters and so we are faced with a closed system.
In cases like this we use the type of system that emgardener had recommended : 4 inch perforated pipe set at 2% in a field of drain gravel covered by a silt blanket . The perf pipe is connected to a solid exit pipe and directed out of the enclosed box.

What about using hardware cloth or window screening to keep the medium inside the planters, and using a larger particled, more inorganic medium, such as a mix between the Gritty and the 511, which wouldn't break down incredibly fast, and would give about a two, or possibly three year rest in between redoing... there might even be a way to insert wicking that emerges just enough to pull moisture out the given drainage holes...

I'm no expert... just thinking off the top of my head, and guessing what I would do in that situation.

Whomever planned this didn't plan with the trees' health in mind...

Or... using quick-crete, create a gradient higher at the back of the planter (inside it, of course), down to ground level in front, so any moisture drains toward the holes through gravity... I would still use a more inorganic medium that holds its structure, and I'd still utilize something to hold in the medium, as tapla suggests.

On the other hand, someone with a multi-million dollar estate might decide to rip out the trees in a year and put something entirely different in... one can never tell. ;-)

I'm just going to place enough gravel near drainage holes to augment the filtering of the fabric I place over it and test the drainage. Because of the height of the planters the drainage will probably be better than the pots I use in my nursery, but I will test it before placing the trees into the planters. I don't see why a planter would require a more elaborate drainage system than a plastic pot. The three outlets the mason provided have probably about the same relative area as what's provided by pots.

You folks suggesting my mix will have a lot of shrinkage are mistaken from my own experience which represents quite a few years and hundreds of large pots. As I stated, only the peat will quickly break down- the compost is pretty stable and perlite and sand aren't going to shrink any time soon.

Thank you all for your help and I will let you know the results of whether I end up needing a more elaborate drainage scheme.

best of luck and we look forward to hearing how things worked out.

I tested the planters for drainage after simply spreading a bag of marble chips behind the drainage holes of each container and placing fabric over that then filling with my mix.

Seemed to drain fine for now so I transplanted pears into the mix bare root, saving most of the rootsystem. Pears are very reluctant transplanters so that is my main cause of concern. Any other species I work with move bare root fine but pears have very little in the way of small fibrous roots making their transplanting more tenuous.