This article is from the Rose Gardening FAQ, by Bill Chandler firstname.lastname@example.org, Jolene Adams email@example.com, Brent C. Dickerson firstname.lastname@example.org, Karen Baldwin email@example.com, and many contributors
Roses appreciate lots of water. Water generously, at least 1 inch/week,
preferably 2 inches/week during growing season. Water every 4-7 days during
the summer when needed. Each bush needs about 4-5 gallons/week during the
Roses get all their food either through their leaves (foliar feeding) or
through their roots. The only medium for transporting food is water.
Infrequent deep watering is preferred to frequent light watering to help
promote a deep root system. Deep root systems help the rose to survive both
droughts, and winter freezes. Frequent, light watering causes roots to form
very near the soil surface, making the plant more susceptible to summer
'baking' and winter freezes.
Try to avoid getting the leaves wet (which promotes disease) when watering
late in the day. However, on hot days wetting the foliage can reduce
transpiration and relieves heat stress.