Answer: These shrubs are very sturdy plants with a strong root system. I would wait until either late August or the end of winter to move them. Water them deeply the day before so they are well hydrated for the move. Dig as much of the root ball as you can, (start at least a foot away from the stems -- two feet would be better -- and dig down a foot or so if you can) then use a tarp or wheelbarrow to move them. They will be extremely heavy. Replant immediately at the same depth as they grew before, water thoroughly to settle any air pockets, mulch, and then water as needed to keep the soil damp until they re-establish. You will probably also need to trim them back quite short to compensate for the roots lost in the digging process. This is not such a terrible thing as old spireas can benefit from a severe cutting back (literally very close to the ground), this causes them to regenerate with vigorous new growth. If you trim them back they will not bloom next spring, but they should bloom the next year. GOod luck with the move!
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