I don't know about Am. Beautyberry but I cut my Blue Mist Spirea (assuming you mean Caryopteris?) to within 8" of the ground every year. If you don't they get very overgrown. The growth is amazing on this thing.

Sharon

I have the Japanese Spirea but I don't know the exact name. They were bought at a plant sale with no tags. I cut mine back in the summer after flowering but I don't like the cropped look after cutting back.

I have 3 of these bushes and they are just start to leaf out so I am going to do some experimenting by cutting one back now and judging the difference in a few months.

I have always been confused about the pruning of spiera.

I trim my Blue Spirea, which is NOT the same family as Japanese Spriea. I just trim my Blue Spirea back to even it up on top, remove winter killed tips. I don't do much trimming of the woody stems, except to open the center a bit for air movement. My Blue takes a long time to get woody growth, so I don't want it removed.

I am going to trim a few stems at the bottom to open up bush center, then even the top tips for height, on the American Beautybush. It blooms on old wood, so I try not to remove much from bush. I do want to allow total stick length, of all sticks, to get sunshine and flower, for the most berry appearance in fall.

I shear my Japanese Spirea early, just as the buds are starting to break open. Don't wait for leaves to grow. I cut my Japanese down to about 8 inches high, flat on top. Cutting too late makes bush waste a lot of energy putting out new leaves that you will be cutting off.
I do thin to remove some of the old center sticks of Japanese Spirea to the ground, for keeping bush open, airy. Shearing tops flat, causes the sticks to put out new leaf growth entire stick length. New tops with soft branching spread well, which is where the flowers appear. Causes bigger flower flush. The new leaves also have a LOT of great color, making bush a focal spot before they bloom pink. I get all new growth on top, good spreading branches, so bush is back to original height by fall.

All three of these bushes are trimmed early Spring, before leaves get any size to them. This preserves stored bush energy. Bush needs the stored energy to put on new leaves and replacement growth that bush will be able to keep and use.

My bushes are on the "to be whacked", list this week. It's time, here in mid-Michigan.

Re: Beautybush: If you are referring to Callicarpa dichotoma, they should be cut back like Buddleia. If you are referring to C. bodnieri, they shouldn't be cut back.

I cut back blue mist spirea (Caryopteris) at the end of April, the same time as lavender. It's one of the last woody sub-shrubs to leaf out for me, so cutting it back any earlier puts it at risk for late cold spells. I take it down to a small woody framework, leaving only a couple of inches for each stem coming out of the main trunk. This treatment has kept it blooming strongly on new wood. Caryopteris 'Worcester Gold' likes to be shorn down like the Japanese spireas; it doesn't get leggy and will have better color. These plants love dry, poor soil; a hedge of blue mist shrubs has self-sowed along my gravel driveway.

Good luck!