May 7 is the average last date of frost for Richmond so planting outside 2 weeks later than that should be ok. Should a frost still show up even later than that, you can cover the plant. Any damaged leaves (by frost) will be replaced and the plant will not be lost although it might look yucky-ish for a little while. Maintain 3-4" of mulch year around to protect the roots, conserve moisture and lengthen the times when you have to water. Start with a 0.5 - 1 gallon of water but add more if your soil is sandy. Then test the soil with a finger at a depth of 4" weekly. When it feels almost dry or dry then water again. Add more water as temps warm up and reduce watering in the fall and winter. Watch for signs of leaf sunscorch in the first summer and either protect or transplant. Pay attention to leaf wilting during the first summer too. In the lower half of the country, fertilize in May and July. In the northern half fertilize once in June. You can use a cup of cottonseed meal or one application of a general-purpose slow-release chemical fertilizer. You did not mention what type of hydrangea this is so I assume it is unknown. Planting it early will help acclimate it to your area as soon as possible. This is important because you have some pockets of Zone 5 areas in Virginia. Winter protection may be necessary on every Fall if you notice in Spring 2011 that the plant stems died (dried out) thru winter 2010-2011, that all growth started again from the base or crown, and that there are no blooms in 2011.