Answer: Bloodgood (Acer palmatum var. atropurpureum) `Bloodgood`is described in the catalog as: Attractive foliage with burgundy-red coloring turns brilliant scarlet in fall. Interesting blackish-red bark. Slender, airy form well-suited for use as a small lawn tree or for patios and entryways. Deciduous. Filtered sun. Moderate grower to 15 feet tall and wide. Grafted. Summer heat zones 1 to 8; winter hardiness zones 5 to 8.
Emperor (Acer palmatum `Wolff`) is described as: Attractive foliage with rich dark red coloring in summer turns brilliant scarlet in fall. Interesting blackish-red bark. Airy form well suited for use as a small lawn tree. Additional cold hardiness allows leaf buds to appear later in spring, avoiding danger of late frosts. Deciduous. Filtered sun. More vigorous grower than others to 15 feet tall and wide. Grafted. Heat zones 2 though 8; winter hardiness zones 5 through 8.
I think the key differences are vigor and the fact that Emperor leafs out later in the spring. If you live in an area that tends to have oscillating temperatures in the spring, this can be a particular benefit in avoiding cold damaged buds or leaves. They are both lovely trees. You might look at them in real life and decide you prefer one over the other -- the foliage shape and coloring is a bit different. There are close-up photos at the web site, too, but it is a subtle difference. Whenever you begin to compare fairly similar cultivars of Japanese maple like this, the small differences become more noticeable. You might check with your local county extension and professional nursery staff to see if one or the other seems to fare better in your local climate and soil conditions. As I said before, they are both really nice cultivars.
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