I don't think you have to move right to questioning his competence. I would check first what assumptions each of you is operating under. If you have given him instructions to produce a certain kind of environment in the yard, shade may be an essential part of that and perhaps he can't produce any other source of shade in the short term and is concerned you'll not be happy with the outcome if there isn't enough shade. Or something. He may also be making some assumptions about how much you want to water your plants. I de-shaded the north side of my house with the removal of a tree and it does get sunny as the sun veers around in the afternoon. New trees are just growing in enough to make an impact 4 years later. If there is a chance you will be removing the big tree at some point within 5 years, the pot is a very good idea for another reason - you'll have to get the little maple out of the way of falling tree parts. They do grow well in pots, especially if the pots are big enough. KarinL

There is no way a pre-emergent herbicide can distinguish between weeds and what we may consider non-weeds. They are simply all broadleafed plants and the effect should be the same. That's why it is not recommended to use pre-emergents where you will be sowing seeds or allowing self-sown seeds to germinate. I would attempt using Preen or some other pre-emergent before I'd resort to RoundUp, even in clear areas under the tree canopy. There is some evidence that repeated use of RoundUp across a tree's root system can have damaging effects. I realize you may be dealing with a great many seedlings, but I'd recommend manual removal over and above anything else. I deal with freely seeding maples myself and understand what a PITA it is to get rid of them. Raking up the samaras when they fall would be my first step. The less of these that remain on the ground, the less germination that will take place and many fewer seedlings to deal with.

Both of my maples are fairly young, probably 5-6 years old, 3-4 years at the nursery and 2 years in a ground. In full sun plus reflected light off the house, 'Mushroom' form is usualy formed by removing single leader at the crotch, though sometimes leader just aborted naturaly or never develops (that is why you see more 'mushrooms' than 'trees'). Eventual (approximate) height of the 'mushroom' determined by the height where the leader was cut off. Very open bright shade, In a fall both of them will have a same color, identical to this one. 15 years old Inaba Shidare from the neighbor's yard in a fall, One more time, before you spend big bucks at the nursery, check HD or Lowes, at this time of the year they should still have them. At least mine does and prices are in $59-129 range depending on a size. In a fall they will be in stores again. Good luck.

If this is to be the permanent home for the Osakazuki, I might reconsider that siting. Osakazuki gets to be a big JM - one of the largest growing cultvars - and is really more of a specimen tree than something that could well be overshadowed by a much larger growing nearby red maple. I'd be inclined to give it a space all of its own so it can really shine. Maybe somewhere with a more evergreen backdrop so the gorgeous fall coloring Osakazuki produces will be really be highlighted.