why do my acers keep dying

Acers are woodland plants - they like humus rich soil, moisture, some shade from the midday sun, particularly in summer, and some protection from cold northerly or easterly winds. Planted near bay tree, conifers and ivy it probably wouldn't like - imagine the soil will be too dry for it. In a pot should have been fine, if the pot was big enough, had drainage, wasn't in full sun, the compost was slightly acidic and not limey, and you kept it watered well enough (which is usually the problem - people don't water properly!)

...and try to use rainwater.

People are often surprised to learn that small acers are in fact quite prone to slug damage - slugs chew the bark at or just beneath ground level and if they chew off the bark in a complete circle arll the way round, then the tree dies. Check the very base of the trunk for damage.

Tagging on to what Bamboo has said, over watering can also be a problem in a pot. If the root ball is relatively small, it can take a while for these roots to get out into the surrounding compost if put into too large a container. If this compost is constantly being kept wet, the root tips can start to rot off and the plant will fail. I have seen this soooooo many times with customers where i work.

The only way around this is to move your plants up gradually each season into a slightly bigger pot allowing the roots chance to invade the compost. They can then be watered quite heavily to no ill effect as they suck the water up quickly.

In the open ground, there should be no problem as water is always moving gradually through the soil by osmosis and unless you have a drought, watering should be kept to a minimum except at the initial planting and maybe a couple of times after that.

I am not in total agreement, Fractal, with your watering suggestions for the open ground for new/relatively new planting - I have a blog on watering, Wildcat, its' not very long, and you can find it by clicking on my icon, which gets you to my profile page, and click on blogs - there's only 4 to choose from.

I'll have a look at your blog Bamboo.

Just had a look at your blog on watering and it all rings pretty much true to what I would suggest. Regarding the Japanese Acer (which I presume this is for) I still hold with what I said except I should have made it clear that any watering should be thorough as you also say, making sure that you give a really good soaking. I should perhaps have also mentioned a good mulch around the base of the plant with composted bark would help retain moisture.