Answer: In your area with hot summers, the Hydrangea paniculata 'Grandiflora' would be better in partial shade, which would mean direct morning sun or very bright dappled light all day. This might or might not be the reason it does not bloom however. If it is not wilting or showing signs of heat stress, it may be fine in the location where it is in terms of light. (In too much shade it will not bloom well.)
A new shrub would need a year or two to settle in and become fully rooted and established and begin to bloom its best. This shrub does best in rich soil that is evenly moist yet well drained, meaning not soggy or saturated. If it is in dry soil, this could stress it and slow its rooting and establishment process.
And once established, a regular fertilization program and deep watering during dry spells will increase the blooming performance. You might try giving it an annual top dresing of good quality compost along with a general purpose or slow release fertilizer each spring. (Read and follow the label directions.) Water it as needed to supplement rain and keep the soil moist, and use an organic mulch year round. The mulch should be applied in a flat layer several inches thick over the root area, do not allow it to touch the stems. This will also help feed the soil slowly as it breaks down over time.
This shrub blooms on new wood, so avoid pruning it during spring or summer as this is when the flower buds for the current season will be forming.
If you think it is in too much sun, such as sited in afternoon only sun, you might consider transplanting it to a location in morning sun. Water it well the day before you dig it, take as much of the roots as possible, and replant immediately. It is too late to move it this spring, but you could move it this coming fall.
I hope this helps.
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