Amending a planting hole in clay soils is asking for trouble. Picture a bucket filled with compost or good quality potting soil.....what happens to the excess water after you water or it rains? Japanese maples do not necessarily mind clay soils - they tend to be nutrient rich - but they do resent poor drainage. In fact, it is pretty much the kiss of death. When dealing with clay soils, if you want to amend, amend the entire planting area, not just individual holes. Otherwise, dig a wide but shallow planting hole, place the tree in high (top of rootball above grade) and mound excavated soil up to the top of the rootball, creating a small berm. Any amendments you wish to add can be used as a topdressing. Vibrant color depends on cultivar and sunlight. Filtered or light shade is good for any variety, as is morning sun. That is usually sufficient to develop very satisfactory coloring on any cultivar. You should be aware that most JM's have at least 3 distinct colorations - early spring or any new growth (which can occur anytime), mature midseason leaf color and in fall. Of the three, midseason coloring tends to be the least dramatic with new growth and fall color competing neck and neck for intensity, depending on specific cultivar.

Well... 'Atropurpureum' is suppossed to be seedling grown, and seedling grown trees are variable. So one tree might be redder during the year than another. Still good trees thou. Sounds like you are moving the tree in a pot...? Few hours of direct sun will help. Once the tree goes greener it won't turn back to reddish, leaves should turn red in autumn obviously.

From the photo it appears that you have a small Acer palmatum dissectum. It is true that you will do minimum damage to the plant by moving it after the leaves have dropped, in the Fall, when it is dormant. At this point, the plant's energy reserves/food supply for its Spring flush is stored in the root structure. By the size of the plant I would suggest digging a root ball about 1 ft in radius [two feet across] and at least 1 ft deep. Prepare the new hole first, a bit larger, with some fine filling soil on the side. Once you dig the tree, move the root ball quickly, minutes count, to the new location. Make sure it is a snug fit in the new hole by adding filler soil around the perimeter, then light pess into place with your foot. Give it a single watering just to settle loose soil and remove any large air gaps.

Gardengal, Thanks for the comparison to grafted plants pots and the reminder about bark based compost. It almost sounds like I could leave the plants in the 4"x9" they are in now for another year. That would be nice. Re: "Varieties" I sort of didn't think about seeds not being 100% true to the parent plant, and I would not call them the original. But having said that it's hard NOT to call these guys 'varieties'. There is an obvious difference between the little guys that resemble the parent pretty well. I have 6 little red ones from a Sherwood Flame that look identical to one another, 6 pinkish-green Japanese maple trees from a Sango Kaku, and 1 from a Seiryu... . So yeah they are not official but hey you can't beat the price----and they are absolutely beautiful! Maybe I'll give them each a unique name, like Bardamu's Rufescent Sprout, etc then sell them on eBay. There are so many varieties, and I sure can't tell what's what in this crazy world. Ken, I'm not any more worried about these plants living through this winter than with my other potted plants--which is a substantial concern. But here I didn't bring it up. I just wanted to know an acceptable pot size for a 2 year old JM tree for next spring. I live in Southern Massachusetts in a spot I like to call z6. I really should put that in my nickname. Since the generic acer palmata are in a small pot now, I am burying the pots in ground under a wind shelter, so I think I've got that part covered---or I am in for an unpleasant surprise!