Adequate watering roses, ideally in combination with fertiliser, is important in determining the quality and extent of new growth. The quantity and intervals of watering depend not only on rainfall and on the soil type and thickness of the mulch, but also on temperature.
Irrigate thoroughly once a week in moderate weather.
Every day during very hot periods to cool down the plants as well as to compensate for the loss of moisture from evaporation.
At all times, make sure that the irrigation period is sufficiently long for water to penetrate the mulch and soil and reach the roots.
Lack of water
Unsatisfactory performance can often be attributed to lack of water, even when plants are watered every day.
Water can be prevented from penetrating down to the roots if, for instance, there is too thick a layer of mulch; or if the plants are irrigated with too fine a spray and for too short a period for water to roll off the leaves and reach the roots.
On slopes or embankments, it is essential to create a basin or place a half concrete ring on the lower side of the plants in order to hold sufficient water to penetrate down to the roots.
Trees nearby may send their roots into the rose bedding and will take all water and suffocate the roses.
The quality of the water can limit rose growing in some regions. When irrigation water contains relatively high proportions of sodium combinations (known as brak water), the absorption of some micronutrients, such as iron, is blocked and the leaves manifest a light-green to yellow appearance. If the sodium in the soil is not flushed out occasionally by rain water, the situation compounds and the roses deteriorate further and may die.
Overhead or subfoliage irrigation are both acceptable, although moisture from overhead irrigation can spoil open blooms.
Watering should not take place late in the afternoon during autumn or on overcast days, as water standing on leaves for several hours causes germination and penetration of black spot spores.
Rain is irrigation from heaven. It is nevertheless advisable to ensure that rain has indeed been sufficient to penetrate deeply (at least 15 mm), otherwise additional watering becomes necessary.
An irrigation system is essential in a rose bed, if not for the whole garden.