Why Do My Roses Lose Their Leaves In The Summer?

Hybrid roses are more susceptible to losing their leaves than are shrub and antique roses, which are more hardy.
Make sure your roses are planted where they can get plenty of air circulation and at least 5 hours of direct sunlight per day.
You can cause leaf dropping and blackspot,(if you live in a high humidity area), from watering the branches of your rose bushes.
They should always be watered at the base of the plant.
Over watering will cause the leaves to turn yellow and drop off, also.
Too much water will cause root rot and can cause your rose bushes to die.
Water deeply, two times per week.

You should check the place where your rose pot is placed, either it is placed where sun rays fall directly or it is not being watered properly.