Prune in early spring.1
Try to plant in a location that enjoys partial sun and remember to water moderately. Keep in mind when planting that Red reiter is thought of as half hardy, so remember to watch your frost dates and ensure you have this plant protected when the temperature dips.By our calculations, you should look at sowing Red reiter about 63 days before your last frost date.
1 monrovia.com/plant-catalog/plants/10/red-flowering-maple/