When it comes to having successful roses I consider there are two main factors. Wise variety selection and how they are watered.
How much water does a rose need? What a hard question to answer. Do you want flowers all year round? Are they bush roses, climbers, standards, old fashioned or miniature? What other plants are around and are trees present? What soil type are they growing in? Are they growing in large pots? What restrictions are there for watering in your area? Each question will give different answers so all I can offer is basic advice and let you work out how it relates to your particular situation and garden.
Working on normal soil without any competition and a typical bush rose this is the recommendation. With sandy soils apply more water. Climbers need more while miniatures less.
Generally roses are one of the world’s most drought resistant plants and where they originate from in countries such as Turkey, Iran, Afghanistan and China watering would only occur spasmodically over the year. Yet they survive.
The most basic of roses are the old fashioned roses. These varieties will give exquisite flowers of various styles on bushes of various sizes in the months of November and December. Depending on where you live there is no need to water these plants at all for them to bring delightful flowers to the bushes after winter rains. To keep them healthy and foliage fresh I would recommend a deep soak several times over the summer if no natural rain falls. A deep soak is with drip irrigation at 1 to 2 litres per hour for 6 to 8 hours. Rose types in this area are Alba, Centifolia, Gallica, Damask and Species.
In an average garden we see modern roses account for the majority of plants seen. These varieties do have the ability to flower over a longer period of time and hence do require larger amounts of water for continued flowering. Again working on the majority of the rose growing areas of Australia, winter rains do give enough moisture in the soil to create flowers in November and continue right up to Christmas in a typical year with no need to add further water. If the plants do start to look dry with the growth lacking softness to the leaves, the first watering may need to be made earlier than normal.
For these types of roses I would suggest a deep soak of water by drip irrigation with an emitter of 1.2lt of water per hour for 4-6 hours every few weeks. Please remember surface watering encourages surface roots which will see the plant suffer in times of severe heat needing more water for their survival. Watering should be continued through summer until the weather reduces its heat and autumn rains start to fall. Remove old flowers with a short stem at any time keeps the plants fresh. Good rose varieties should have plenty of flowers over the whole season.
It must be remembered, the larger the plant the more water it needs, the smaller the plant the less it needs. Remember other plants in the garden especially trees can rob roses of moisture they need. Always mulch well to reduce moisture loss from the soil which also gives nutrients back to the soil. Adjust your watering to find the right balance for what you require from your plants.