Hi there, We did this around our potager. We dug down about 3-4 inches to level, used a hand tamper to compact and laid lanscape fabric to suppress weeds. It's held up nicely for four years so far. Few weeds root in the gravel, but easy to pull. We haven't had to top up the gravel yet, but may do so in a year or two. As to what to use, this terminology seems to differ by region. I've heard it called crusher run, road mulch, etc. You can ask for 'quarter inch minus" which means a mix of larger pieces (but no larger than 1/4" plus fines and small stuff). You do NOT want pea gravel or anything too large which is shifty underfoot and a pain to drive wheelbarrow through, etc. HOpe that helps.

Yes, raised in the middle makes a crown. How much, is your call. You asked about the shape. I like to think of the shape of a lawn as if it were water. A pond in your case. Being fluid really helps with giving the lawn 'flow' and 'presence'. Everybody worries about the shape of a tree or rock, but usually don't give much thought to the shape of the lawn except to cover as much space as possible. Then they cutout flower beds and they end up looking like cutouts. The shape of the lawn is more important than the shape of the flower beds. I hope that helps. I haven't been in downtown Seattle in 5 or 6 years. I used to live within walking distance of the market. I'm sort of an old hermit in the country now. The last time I visited the Calgary area I visited the Drumheller Dinosaur Museum. Awesome!

I guess if you purport to speak with more authority on the subject than those who spend all their time researching and studying these issues, Embothrium, then feel free to call that false. OTOH, I tend to give more weight to opinions of actual horticultural scientists : "Let's say you have incorporated the recommended 25-50% organic matter to your backfill. (Remember that an ideal soil contains 5% organic matter by volume.) The initial results are positive; roots grow vigorously in this ideal environment as long as irrigation is provided. But what happens when these roots encounter the interface between the planting hole and the native soil? Native soil contains fewer available nutrients, is more finely textured and is less aerated. Roots react much in the same way as they do in containers: they circle the edge of the interface and grow back into that more hospitable environment of the planting hole. The roots do not establish in the native soil, eventually resulting in reduced growth rates and hazard status as crown growth exceeds root ball diameter" The Myth of Soil Amendments, Linda Chalker-Scott, PhD

There are several issues inherent in using large fractions of topsoil and coir in a medium intended for use in containers. The main ones are excess water retention and insufficient aeration. The excess water retention can be fixed as easily as judicious use of ballast or partially burying the pot into the ground such that the bottom of the pot is a few inches below the grade level. This turns the entire earth into a giant-size wick and will remove all or nearly all excess water. While this increases o/a air porosity by virtue of the conspicuous fact it removes excess water, it still might not ensure there is enough air porosity to keep the plants content. Coir doesn't retain loft well (it compacts easily), and holds more water than peat. There are also chemical considerations associated with using significant fractions of coir and CHCs in potting medium (more than 10-20%). All coir/CHC products are very high in K, very low in Ca, and have a potentially high Mn content, which can interfere with the uptake of Fe. Several studies have also shown that the significant presence of phenolic allelochemicals in fresh coir/CHCs can be very problematic for a high % of plants, causing poor growth and reduced yields. The pH of coir/CHCs is high enough that the use of dolomitic lime is precluded as a source of Ca/Mg, and both have potential to have excessive EC/TDS (salt) levels. Repotting now would require you free yourself from the dogmatic convention that you should never remove top growth when you repot or transplant. That's fine advice when all you're doing is dropping a B&B tree or a tree fresh out of a nursery can into a hole in the ground, even though that's a decidedly poor strategy as well, unless you bare-root and correct root issues which brings you full circle to the fact it's pretty much necessary to significantly reduce trees' top mass or completely defoliate if you do significant root work, and especially if you bare root. Appropriately reworking the roots requires your tree is healthy enough it has enough in the way of energy reserves to push a new flush of growth. If you fear it doesn't due to recent/current low vitality levels, best bet would be to remove the tree from the pot as is and put it in the ground until just before bud movement next spring, at which time it can be relifted and the root issues corrected w/o need to reduce the canopy. This is true because quiescent buds of deciduous trees tend to remain in that state until the tree's chemical messengers signal plant central the volume of roots is sufficient to meet the water needs of new breaking buds coming on line. Al